Evolution Exam 3 Ch. 10-13

Which sex would you expect to experience greater sexual selection when... 1.) the mating system is polygynous? 2.) the mating system is polyandrous? 3.) the mating system is monogamous?

1.)

What three conditions must be met in order for a trait to evolve in response to natural selection?

1.) Phenotypic variation 2.) A genetic basis that can be passed down from parents to offspring 3.) Functional importance of phenotype

Consider traits like... Number of offspring Size of eggs/embryos Age at first reproduction Lifespan? 1.) How would you expect these to vary high versus low predation environments? 2.) How might this apply to overfishing?

1.) Release from the risk of predation led to the evolution of (guppies) that took longer to mature and became larger in adulthood producing fewer and larger offspring per litter. 2.)

Which sex would you expect to have higher variation in reproductive success when... 1.) the mating system is polygynous? 2.) the mating system is polyandrous? 3.) the mating system is monogamous?

1.) The low cost of sperm can make polygyny a good strategy for males because they can fertilize many females which can bear many offspring. However, each male has to compete with lots of other males. 2.) Polyandry can benefit females in a number of ways. By mating with a number of males, females may be able to get the highest-quality genes possible for their offspring. Females may be benefiting not from good genes but from genes that are simply different from their own. If animals mate with partners that are too similar genetically, their inbred offspring may have lower fitness. Mating with multiple males may allow females to boost the health of some of their offspring by giving them a defense against a wider range of pathogens. 3.) Under some conditions, a male may actually be better off mating with a single female, trying to fight off other males, and helping to raise the offspring.

Considering examples of pre-zygotic reproductive isolation... 1.) How might the timing of reproduction be important for broadcast spawners? 2.) How could pollinators play a role in the evolution of reproductive isolation? 3.) What about mating rituals/displays? 4.) What does mechanical isolation refer to? Consider carabid beetles

1.) Timing can also create reproductive barriers. A striking case of isolation by time in corals. Coral reefs are actually giant skeletons secreted by colonies of tiny animals related to jellyfish and sea anemones. To mate, corals release sperm and eggs that drift through the water. The odds that a sperm and egg will meet are highest during this spawning event, because the density of gametes is high. With time, the gametes get dispersed by ocean currents lowering their concentration, and the probability of sperm-egg encounters goes down. Spawning times of closely related, sympatric corals are separated by 1.5 to 3 hours. The density of the gametes from the first spawning species is so low when the second one spawns that the two species are not likely to cross-fertilize. 2.) Many species depend on pollinators such as bees and birds to carry pollen (which contains sperm) to other plants, where it can fertilize the eggs of a flower's ovules. These pollinators can create pre-mating reproductive barriers between plants. One striking case of this kind of isolation is found in monkeyflowers. M. cardinalis was visited 97% of the time by hummingbirds. M. lewisii was visited 100% of the time by bees. The flowers in each species show some obvious signs of adaptation for each kind of pollinator. Bees have to land on flowers before they can reach the nectar. The petals of the bee-pollinated M. lewisii thrust forward, serving as a landing pad. M. cardinalis lacks the broad landing pads, instead it has a long narrow tube that contains more nectar. The species do not hybridize in nature because different pollinators visit them. Schemske and Bradshaw planted produced hybrid flowers and planted them in the field. They found that bees preferred large flowers low in red and yellow pigments. Hummingbirds were attracted to flowers with lots of nectar and rich in red anthocyanin pigments. Since bees and birds have distinct color preferences they tend to visit their favorite type of flower faithfully. The pollinators dramatically reduced the probability that the pollen from one type of flower could end up on the other. As a result, the specialization of monkeyflowers for different pollinators has become a barrier to the plants reproduction. 3.) Many animal species go through certain courtship rituals in order to mate. Each species may have a distinctive ritual making it unlikely for a male from one species to get a chance to mate with a female from another. Fireflies use flashes of light for courtship and multiple species of fireflies may carry out their courtships at the same time. The males of each species produces a distinctive series of flashes and the females respond only to the ones they find attractive. The males approach only the females that wait a suitable and species-specific period of time before responding with a flash of their own. Distinct male courtship signals combined with corresponding female preferences act in these fireflies as a pre-mating reproductive barrier between species. 4.) Some reproductive barriers are brought about by the very act of mating itself. Ex: Carabus maiyasanus and C. iwawakianus which live in sympatry in Japan. When biologists bring the two species together in the lab, they will mate readily. But once the females have mated, they often die. The survivors produce few eggs. It turns out that it's harmful to their health to mate with males of the other species. Male beetles deliver their sperm with an ornate structure called an aedeagus. It fits into a specialized pouch inside the female. Within each species, the fit is good, but between species it is not. The males get stuck and the aedeagus can break off inside the female tearing her reproductive organs in the process and preventing fertilization. --> copulation (gametic) incompatibility.

What is a niche? Why would competition cause character displacement? (Consider the Anols)

A niche is the role an organism plays in a community. A species' niche encompasses both the physical and environmental conditions it requires (like temperature or terrain) and the interactions it has with other species (like predation or competition). When two species live in the same area and compete for the same resource, selection can push their phenotypes in opposite directions. This divergence is character displacement. When two species overlap, individuals that are similar to the other species will experience intense competition for limited food and nesting sites. On islands where A. carolinensis occurred by itself, the lizards preferred to perch on trees almost a meter from the ground. But on the islands where invaders were introduced (A. sagrei), A. carolinensis began to concentrate their activity higher in the canopy, where they experienced less competition.

Compared to other primates, how is the onset of menopause different in humans? Why might this be the case (2 hypotheses...)?

After about 50 women can no longer reproduce- a phenomenon known as menopause. In chimpanzees, our closest relatives, the fertility of female chimpanzees declines as well, but only at the end of life when their entire bodies are deteriorating due to old age. Female monkeys and apes typically don't live long after their last live birth. Humans are an exception to this rule. Women undergo menopause and may live for decades more. Mother hypothesis: Human babies command especially high parental investment from mothers because they are born helpless and require a steady, energy-rich diet for their developing brains. A woman in her late 40s would have a harder time caring for a newborn than she would in her 20s. Show would have to divide her limited resources between rearing babies and continuing to care for her older children. Williams suggested that natural selection favored mutations that reduced a woman's fertility so that she could focus on raising her older children instead. Researchers also argued that older women who became pregnant faced a much more direct threat to their reproductive success; they were more likely to die in childbirth, leaving their other children at grave risk of dying as well. Grandmother hypothesis: For most of human history, many of the women who were still alive in their late 40s had become grandmothers. By helping her children raise grandchildren, older women could raise their inclusive fitness. Loss of fertility associated with shift in investment to grandchildren.

How did glyphosate-resistant crops change herbicide use in agriculture? What advantages did they have?

After glyphosate-resistance crops were in use for a few years, farmers began to notice horseweed and morning glory encroaching once more into their fields. Some farmers had to cut down fields of cotton rather than harvest them, due to infestations of weed called Palmer amaranth. Other farmers had to abandon glyphosate and turn back to older more toxic herbicides. Scientists had thought that glyphosate was invincible in part because the enzyme it attacks, EPSPS, is similar in all plants. That uniformity suggests that plants can't tolerate mutations to it. But it turns out that one mutation, which has independently turned up in many populations of ryegrass and goosegrass, changes a single amino acid in EPSPS. The plant can still survive with this altered enzyme. And glyphosate has a hard time attacking the altered form of EPSPS thanks to its different shape.

How does Fisher-Zahavi process vary from these models (runaway selection and good genes)?

Alleles for female preferences can coevolve with alleles influencing expression of costly indicator traits in males. Although genetic correlations between female preference for a male ornament and its degree of expression have been found, these ornaments are costly indicators of male quality. Thus, a Fisher-Zahavi process of linkage disequilibrium between ornament and preference applies to a "good genes" indicator trait.

How is allopatric speciation different from sympatric? Which one requires a physical separation?

Allopatric speciation is the result of geographical/physical isolation. A population begins with continuous geographical range. It contains genetic variation, but gene flow ensures that new mutations can spread across the range once they arise. A geological barrier like a river divides the population into 2 subpopulations. The change of allele frequencies in the 2 subpopulations is no longer linked. They become increasingly divergent. The river later dries up, allowing the 2 subpopulations to make contact. During their separation, reproductive barriers may evolve reducing the gene flow between the 2 subpopulations. Sympatric speciation: reproductive isolation evolves without geographic isolation. Requires nonrandom mating based on genetic or phenotypic factors.

Genetic evidence suggests that Red deer and Elk are separate species- why would those applying the biological species concept say that they aren't?

Allopatry: occurs when populations are in separate non-overlapping geographic areas (i.e., they are separated by geographic barriers to gene flow). According to the biological species concept, allopatry alone is not enough to warrant dividing two populations into separate species. Populations must also be unable or unlikely to interbreed, even if they were given the opportunity. While elk and red deer do not interbreed on their own, they can when they are brought together in zoos. That's because they are still very closely related. Even though they are geographically isolated, they have not evolved any intrinsic barriers to reproduction.

What is an extended phenotype? Could you provide examples?

An extended phenotype are structures constructed by organisms that can influence their performance or success. Although they are not part of the organism itself, their properties nevertheless reflect the genotype of each individual. Animal examples include the nests constructed by birds and the gall of flies. Female gallflies lay eggs into the growing tips of goldenrod. After the eggs hatch, each larva bores into the bud tissues to feed. The larva secretes fluids containing proteins and other molecules that change the gene expression of cells in the plant. The plant cells grow into a gall. The gall is made of plant cells, and yet its growth is controlled by the flies.

How does Fisher's frequency-dependent selection apply to the sex rations of offspring (for animals that can control them?) 1.) When would having more female/male offspring be an advantage?

Animals can maximize their fitness by adjusting the ratio of sons and daughters away from the typical one-to-one proportions. ---> Imagine that mutations arise in a population that lead to more female births than male births. The imbalance gives males an advantage; a male is more likely to find a mate than a female. If some individuals produce more sons, they will be favored by natural selection. But, as the numbers of males come to equal the numbers of females in each new generation, the advantage of being male dwindles. The same process would work under the opposite conditions, with more males than females. The sex ratio of the population balances itself at 1:1 an example of frequency-dependent natural selection. 1.) If a female is in good condition she may be able to boost her reproductive success by having more sons than daughters. Her sons, in good condition themselves, will mate with many more partners and give her more grandchildren than daughters would. If a female is in poor condition, she may be better off having more daughters than sons. Sons in poor condition may fail to attract any mates at all and may therefore leave their mother without any grandchildren. Daughter, on the other hand, will probably have at least some offspring even if they are in poor condition.

What is anisogamy? How does this influence the presence/strength of sexual selection? How might this influence which sex is responsible for parental care (consider investment risk if offspring die)? How can anisogamy affect the operational sex ratio?

Anisogamy refers to sexual reproduction involving the fusion of two dissimilar gametes; individuals producing the larger gamete (eggs) are defined as female, and individuals producing the smaller gamete (sperm) are defined as male. Males can produce many more gametes than females because sperm are much smaller than eggs. Anisogamy has far-reaching effects on the evolution of males and females because it means that the best strategy for reproductive success for males is not the same as the best one for females. Because sperm are so abundant, the reproductive success of females is almost never limited by the availability of male gametes. Females are limited by how many eggs they can produce and provision--> Fecundity. Females differ in their fecundity, and that difference can determine which individual females contribute the most copies of their genome to future generations, In many populations, the most successful females are the ones who provision more eggs than other females. Males are limited by the number of mates they an obtain. Another consequence of anisogamy is that females often benefit when they perform additional parental care. Females already invest more than males by virtue of their large, yolk-rich gamete, and their reproductive success is most limited by the number and quality of offspring they can produce. A female who continues to invest in the nourishment or protection of her offspring may be able to raise her reproductive success. One reason maternal care is so often beneficial is that when a mother invests in her offspring, the beneficiaries of her care are very likely to actually be her offspring. Males certainty of paternity may be much lower than a female's certainty of maternity. As a result, when offspring require extra care, the females usually provide it. Males typically don't experience such strong selection for investing additional care in offspring. These different potential reproductive rates mean that at any moment, there will be more members of one sex in a population ready to mate than there are potential partners from the other sex. Typically, a population has more available males then receptive females. Slower rate of reproduction by females leads to male-biased OSR

How might sexual antagonism lead to speciation in allopatry?

Antagonistic coevolution of males and females can drive speciation by creating a postmating, prezygotic reproductive barrier to gene flow. When two populations become geographically isolated the males and females in each one will continue to experience sexual conflict. They will continue to accumulate new mutations some that allow males to overcome female defenses and others that allow females to exert more control over their own reproductive success. Within each population, the males and females will remain in a stalemate with almost every attack protein counterbalanced by a female countermeasure. But if individuals from those 2 populations mate, the females may not have sufficiently specific defenses and as a result successful interbreeding will be rare. Various studies have confirmed that sexual conflict can create major barriers to gene flow.

How does the Red Queen hypothesis justify sexual reproduction... how do Potamopyrgus snails in New Zealand support this idea?

As strong defenses against parasites evolve in hosts, countermeasures may evolve in parasites that allow them to overcome those defenses. Several evolutionary biologists suggested that this evolution of parasites and their hosts occurs in cycles. Parasites strike the most common genotypes in the population of their hosts. The hosts reproduce less or even die off, while other more resistant host genotypes become more common. The most common parasite is now no longer well adapted to the most common host genotype. Over time new parasite genotypes evolve that can exploit this new common host, eventually killing them, and the cycle begins again--> Red Queen effect. The Red Queen effect describes a phenomenon seen in coevolving populations- to maintain relative fitness, each population must constantly adapt to the other. Parasite infects the most common host genotype thrives. Sexual reproduction creates lots of genetic variation in every generation of the hosts by shuffling alleles into new combinations. Among those new variations may be some that are very resistant to the dominant parasite genotype. These individuals will be favored by natural selection and their descendants will thrive. Sexual reproduction is beneficial because it makes the host a moving target for parasites. The New Zealand freshwater snail Potamopyrgus antipodarum can reproduce either sexually or asexually through parthenogenesis. Males are present where they are reproducing sexually and males are common (sexual reproduction) where infection by a trematode parasite was highest.

Under what circumstances could a male benefit from sexual cannibalism?

As the female slowly dines on the male he continues to mate with her and his body's nutrients enhance her fecundity.

What is Bateson-Dobzhansky-Muller incompatibility? Is this pre or post zygotic?

Bateson-Dobzhansky-Muller incompatibilities are genetic incompatibilities in hybrid offspring arising from epistatic interactions between two or more loci. These incompatibilities occur when alleles at different loci can no longer cooperate. Consider an ancestral population with the genotype aabb. In one population A arises and sweeps to fixation. In a second allele B fixes. Now the 2 populations have genotypes AAbb and aaBB. If these 2 populations interbreed they will create hybrids with mixed genotypes such as AaBb. Allele A may perform perfectly well with b and B may work just fine with a. But if A and B are not compatible with each other then these hybrids will suffer lower fitness. Epistatic incompatibilities can thus act as postzygotic barriers to the exchange of genes across populations.

How does sperm competition relate to selection? How might a male win this competition... consider examples we discussed in class.

Because females often mate with more than one male, they can end up with sperm from many males inside them at once. In effect, these sperm compete to fertilize eggs. If one male has a mutation that makes it more likely that his sperm will fertilize a female's egg than the sperm of other males, he will have more reproductive success. As a result, sperm competition has led to the evolution of a number of strategies that males (or their sperm) use to raise their success in fertilization. Sperm competition is a form of sexual selection that arises after mating when males compete for fertilization of a female's eggs. -One way males can increase their reproductive success is by getting rid of the sperm females may be carrying from previous matings. Seed beetles have sharp spines on their penises. When a male pairs with a female who has already mated with another male, the spines on his penis enable him to remove sperm from the earlier male. The longer the spines, the more successful the male seed beetles have at fertilizing eggs. -In deer mice, a male's sperm will join together to form aggregates that can swim faster together than they can individually. -Males can also increase the success of their sperm by keeping other males from mating with females. In some species, males linger around females after mating, chasing off other males that might also mate with them (mate guarding). Male Drosophila produce chemicals in their semen that may kill of the sperm of other males and then make females unreceptive to subsequent mating -In some fly and beetle species, males inseminate females with giant sperm, which fill the entire reproductive tract of the female. This may prevent sperm introduced from subsequent copulations from even entering the female. A number of studies show that females can exercise some influence over which males succeed by selecting sperm among the males they have mated with. ---> cryptic female choice refers to a form of sexual selection that arises after mating, when females store and separate sperm from different males and thus bias which sperm they use to fertilize their eggs.

If bigger (deeper) beaks can crack larger seeds... why would the average beak depth decrease in non-drought years?

Because when heavy rains came, more spurge bloomed which produced lots of small seeds. Birds that had smaller beaks could eat small seeds more efficiently than the big-beaked birds could, allowing them to grow faster and have more energy for producing offspring.

What is antagonistic coevolution (and sexual conflict) between males and females? 1.) is this more common in a monogamous or polygamous mating system? 2.) would you expect this to be more or less common when matings are forcing (rather than equally chosen)?

Both males and females have evolved a number of adaptations to increase their fitness in preparation for mating. Some strategies that are optimal for a male have direct negative fitness effects on females and vice versa. Sexual conflict results in antagonistic coevolution. Sexual conflict is the evolution of phenotypic characteristics that confer a fitness benefit to one sex but a fitness cost to the other. If a male's reproductive strategy lowers the fitness of females, then there will be strong selection on females that can counter their strategy. And males then come under selective pressure to overcome female defenses. Males and females thus get caught in a coevolutionary arms race. 1.) monogamous ---> reproductive organs of ducks in many species males and females bond for an entire breeding season 2.) more common

How are Bt-transgenic crops different from glyphosate-resistant crops?

Bt refers to crystalline protein toxins produced by a family of genes (Cry genes) in a bacteria called Bacillus thuringiensis. The bacteria produce the toxic crystals when they sporulate; and, when ingested by susceptible insects, the toxins bind to receptors in the insects' gut and make them sick. Scientists developed genetically modified crops that carried the Bt gene. When farmers plant these crops, the plants make their own pesticide. It rapidly breaks down in sunlight, and so it does not create dangerous groundwater pollution.

Why would an animal that does not reproduce live longer? Would you expect this to vary between males and females?

Calsbeek and cox ran an experiment in which they removed the ovaries from brown anolis lizards. They then performed the same surgery on another group of females without removing the ovaries, in order to create a set of controls. The sham-operated females invested resources to grow eggs. The females without ovaries grew faster because they had free resources they could invest in growth and were more likely to survive.

What are the advantages of sexual reproduction?

Combining beneficial mutations: by combining alleles of genes from two different individuals, sexual reproduction can bring separate beneficial mutations together in a single individual faster than would be expected if they had to arise spontaneously in the same genome. Generation of novel genotypes: through recombination, meiosis provides an opportunity for paired chromosomes to cross over, creating gametes with unique combinations of alleles. Faster evolution: offspring of sexual parents will be more genetically variable than offspring of asexually reproducing parents. This can speed the evolutionary response to selection of sexual populations and is critical for maintaining resistance to parasites (the Red Queen effect) Clearance of deleterious mutations: sexual populations can purge themselves of harmful mutations because recombination can generate individuals with allelic combinations that exclude deleterious mutations. Asexual populations cannot do so, and they steadily and irreversibly accumulate mutations until a lineage is driven extinct (Muller's ratchet)

Sometimes different species look alike... how did Hebert distinguish cryptic species of the moth Astraptes?

Cryptic species are lineages that historically have been treated as one species because they are morphologically similar but that are later revealed to be genetically distinct. Hebert has been a leader in the development of a method called DNA barcoding for rapidly identifying species. To distinguish between species, Hebert and other scientists have identified short segments of fast-evolving DNA contained within the mitochondria of cells that scientists can examine with relatively little effort. The divergence of these hypervariable segments of DNA is not likely to have caused speciation, but it can act as a marker for a broader divergence over the entire genome. Specifically, it can help discern whether populations are behaving as genetically distinct independently evolving lineages. Skipper butterflies in Costa Rica have a wide range of color patterns as caterpillars. An analysis of their DNA reveals that populations have diverged from one another, indicating a diversity of species that had previously gone unnoticed.

Female choice may be based on indirect or direct benefits, could you recognize and provide exampled of each?

Direct benefits are benefits that affect a particular female directly. -Protection --> ex: protection from lethal injuries by other males (elephant seals), male gives female toxic chemicals that she uses to protect her eggs (rattlebox moth). -Territories and/or nests --> ex: access to good egg-laying sites (dragonflies, frogs), suitable vegetation for nesting (red-winged blackbirds), nests the male has manufactured (weavebirds), territories with good forage (antelope) -Food --> ex: prey food items (scorpionflies), female wats fleshy hindwings of male (crickets), spermatophores (katydids and bushcrickets), female eats male (redback spiders) -Help raising young --> ex: females choose males who are better egg guardians (sculpins), females choose males better at fanning eggs (sticklebacks), females choose males better at feeding nestlings (pied flycatchers) -Reduced risk --> ex: females choose males with large bright red combs ( junglefowl; these males have healthier immune systems Indirect benefits are benefits that affect the genetically quality of a particular female's offspring -male offspring that are more desirable to females -dancing males -showy ornaments

What type of selection (directional, disruptive, stabilizing) does the medium ground finch experience after the drought?

Directional response

What is the domestication syndrome? What characters are associated with it? What may be the root cause?

Domestication syndrome is the characteristic collection of phenotypic traits associated with the genetic change to a domesticated form of an organism from a wild progenitor form. Behavior: increased docility and tameness Changes in coat color Decreased tooth size Changes in craniofacial morphology (juvenile characters) Floppy ears Changes to estrus cycles (nonseasonal and more frequent) Brain: reduced size, forebrain reduced Characteristic of domesticated animals is driven by selection for tameness acting on neural crest cell genes, particularly those affecting cell migration.

What is ecological speciation? Why do the races of fruit maggot flies in the genus Rhagoletis support this model?

Ecological speciation is the evolution of reproductive barriers between populations by adaptations to different environments or ecological niches. Apple and hawthorn trees bloom at different times of the year. In each population of flies, selection favors flies that develop so as to coincide with the host fruit. This divergent selection helps isolate the populations driving sympatric speciation. These ecological adaptations reduce the flies opportunity to mate. Their preferences for different fruit thus created an isolating barrier to gene flow, even though both races lived in the same geographical area.

How are wattled jacanas different from most birds?

Female jacanas lay their clutches of eggs into the nests of males and then abandon them. The male protects the eggs, and later the chicks, and will spend over a month with his brood. Because female jacanas abandon their eggs and males take on the parental care, females are able to recycle faster than males. The result is that these populations have an OSR skewed toward females. Nothing about sexual selection requires that males must compete for access to females. This happens to be the most prevalent because of anisogamy and the associated asymmetry of investment by females and males. In role-reversed taxa like the jacanas, it is females who compete over a limited number of reproductively ready males.

What is the stabile ecotype model (as applied to prokaryotes)? Why might selective sweeps be an indicator?

Frederick Cohan has offered an influential species concept for microbes known as the stable ecotype model. Cohen argues that microbes undergo ecological speciation like animals and plants do. Cohan argues that when lineages of microbes adapt to a particular ecological niche- one that's distinct from the niche of other lineages- it's appropriate to call them a species. These species endure over time because selection strongly favors mutations that enable them to exploit their niche more effectively. When a beneficial new mutation arises in a microbe, its descendants swiftly outcompete other members of the species. Selection thus prunes a species side branches maintaining a strong genetic similarity among its members. Shapiro and colleagues found that some of the bacteria grew in biofilms on small animals and algae, and others floated in open water. Here were 2 groups of closely related bacteria each of which had undergone natural selection for different ecological niche. According to the stable ecotype model, you would expect that selective sweeps would have caused the genomes of the 2 new species to diverge. The mutations that distinguish the 2 species would be distributed across the entire genome. Shapiro and his colleagues propose a variation on the stable ecotype model to explain these results, one that takes horizontal gene transfer into account. The V. cyclitrophicus population started out as an ecologically uniform group of bacteria in which homologous recombination occurred frequently. Then some members of the group acquired adaptive alleles from other bacteria through homologous recombination. As a result, the once uniform population of bacteria began to diverge into 2 groups each with a separate ecological adaptation. As the groups diverge selection favors mutations that improve their performance in their own niche. Homologous recombination continues to occur within each group, but it becomes less common between groups.

Why is the gall size in Goldenrods (induced by the gall fly Eurosta solidaginis) stabilizing at medium sizes? What type of selection occurs and what type is the net result?

Galls give the larvae physical protection from 2 major sources of morality: predatory birds and parasitoid wasps. The likelihood of each of these sources of mortality is influenced by the size of the gall, but in different ways. Bird predation selects very strongly for small gall sizes. Bigger galls are easier for the birds to find. As a result, the fly larvae in large galls get eaten more often than the fly larvae in small galls. Predation of birds favored the evolution of small, inconspicuous gall sizes. The parasitoids also cause strong selection on the galls, but their effect is opposite that of bird predators. Parasitoid female wasps must reach into the center of the gall to place their eggs on the surface of the gallfly larvae. As a result, the larvae in the largest galls often escape being parasitized. Parasitoid wasps thus favor the evolution of large galls. Together they reveal a balance. When galls are too large, galls are likely eaten by birds. When galls are too small, larvae are likely to die from parasitoids. The result is a trade-off with stabilizing selection for intermediate-sized galls. The type of selection that occurs is directional selection in two ways that leads to stabilizing selection Net effects can be a balance: Different agents of selection- pulling on the same trait; stabilizing selection for an intermediate trait value.

How does glyphosate prevent plant growth? How have weedy species evolved resistance?

Glyphosate kills weeds by blocking the construction of amino acids that are essential for the survival of plants. It attacks an enzyme called EPSPS that only plants use, so it is harmless to people, insects, and other animals. And unlike other herbicides that wind up in groundwater, glyphosate stays where it's sprayed, degrading within weeks. Scientists improved the performance of glyphosate on weeds by engineering crop plants to be resistant to glyphosate. They did so by inserting genes from bacteria that could produce amino acids even after a plant was sprayed by herbicides. Instead of applying a lot of different herbicides, farmers found they could hit their fields with a modest amount of glyphosate alone, which wiped out weeds without harming their crops. Weedy species have evolved resistance by altering an amino acid in EPSPS

How is the runaway selection model different from the good genes model? 1.) do they deal with direct or indirect benefits of female choice? 2.) which one does not require an honest signal of male quality? 3.) which one relies on an arbitrary character for the selection? 4.) why is it difficult to show which model is correct?

Good genes: elaborate or bright male ornaments signal underlying genetic quality (good genes) such as efficient metabolism, body condition, or resistance to parasites or disease. Assumes that among-male variation in the expression of ornaments reliably signals individual difference in overall quality of the males. It predicts that choosy females will produce offspring with higher survivorship or in better condition than less choosy females. Ornaments may indicate that males are able to successfully wield costly 'handicaps', are resistant to parasites, or are in top physiology condition. Runaway selection: Certain male traits are advantageous not because they indicate good quality, but because they are attractive to females. Offspring of females choosing males with attractive traits inherit alleles influencing the expression of both the preference (from their mother) and the trait (from their father). The resulting association between preference and trait can lead to a positive feedback cycle of ever-stronger preferences and larger display traits. Ornaments can evolve to such extremes that their severe costs balance the reproduction advantage of having the trait. 1.) indirect benefits 2.) runaway selection (?) 3.) runaway selection 4.) ?

What happens (usually) to three-spined sticklebacks that invade freshwater lakes? What evidence supports your answer?

Heavily armored individuals spread into the freshwater lakes, but then their less armored descendants had more offspring than the heavily armored ones. The mean level of armored plating dropped over time. This evolutionary reduction of defensive weaponry occurred repeatedly in lake after lake.

What is horizontal gene transfer? Why does this complicate phylogenetic analysis?

Horizontal gene transfer is the movement of genetic material between unicellular and/or multicellular organisms other than the transmission of DNA from parent to offspring. Molecular biology has made a species concept for microbes even more challenging by revealing huge amounts of horizontal gene transfer among their lineages. Microbes can acquire genes from other species by several mechanisms. In homologous recombination, a microbe that is repairing a damaged segment of DNA can replace it with a closely matching version from another microbe. Viruses can incorporate DNA from a host microbe belonging to one species and then insert it into the genome of another host belonging to an entirely different species. Plasmids can engineer their passage from one microbe to another. While the chances of any one microbe acquiring genes by horizontal transfer are small, the cumulative impact of the process on microbe has been immense.

How have humans served as agents of selection? On purpose... On accident...

Human-driven selection had its first huge impact on the world when we first started to domesticate plants and animals. The early stages of domestication may have begun inadvertently. Humans selected behavioral traits in their livestock, such as increased tolerance to penning, increased sexual precocity, and reduced wariness and aggression.

How does the involvement of males in parental care affect the OSR? 1.) Will the OSR be more or less biased if males help rear the young? Why 2.) With sexual selection likely be weaker or stronger if males help rear the young? Why?

In species where both males and females cooperate in the care of young, the OSR may be much less male-biased. 1.) The OSR will be less male-biased. If males spend the same amount of time with young as the females do, then they are not going to recycle any faster than the females. Males and females are equally "tied down" with parental care. As a result, the number of males ready to breed will be comparable to that of females. 2.) Sexual selection is predicted to be much more weaker in these populations. In a few species, the OSR is reversed- more females are ready to mate than males.

How did Trivers and Willard apply this to available resources or condition of the mother? 1.) Do the Seychelles warblers fit this pattern?

In their hypothesis, Trivers and Willard proposed that a female could alter the sex ratio of her offspring to suit her condition. Many mammals do just this: Females in prime physiological condition at the time of conception are more likely to produce more sons than are females in poorer condition. 1.) But in some species, females manipulate sex ratios in the opposite direction. Such is the case for the Seychelles warbler. When a mother warbler's egg hatch, the male and female chicks can look forward to different lives. The male birds tend to fly away from their natal home in search of female warblers and other territories. Young female birds tend to stay behind helping their mother incubate her eggs. A mother benefits from this help because she is able to rear more chicks over her lifetime. Female Seychelles can adjust the balance of male and female chicks in their broods in response to their environment. An unassisted female living on a patch of land with abundant food may produce a broos that's as much as 88% daughter. Female warblers that live in places where food is scarce may produce broods in which as few as 23% of the chicks are daughters. A female bird that lives in high quality territory can use the help of her daughters to produce more chicks. A female that is stuck living in a low quality territory will be better off producing sons that can search for greener pastures.

Why would a refuge (where normal not Bt transgenic crops are grown) near transgenic crops help show the evolution of resistance in pests (that eat the crops)? How does this relate to gene flow? To tradeoffs?

In these refuges, Bt-resistant insects would be outcompeted by other insects that didn't invest so much in detoxifying Bt. Insects from the Bt-producing fields and the refuges would interbreed, and their offspring would inherit some genes for Bt susceptibility.

How did David Hoag's experiment with mice and the imprinted genes Igf2 and Igf2r demonstrate the paternal conflict in placental mammals? 1.) What is in the best interest of the father? The mother? 2.) How does imprinting provide a mechanism for this arms race between the sexes?

Insulin-like growth factor 2 (Igf2) is produced by fetus-derived cells that invade the lining of the uterus, where they extract nutrients from the mother. Normally, only the father's copy is active, while the females is silenced. To understand the gene's function, scientists disabled the father's copy in the placenta of fetal mice. Without the Igf2 gene to help draw nutrients from their mothers, the mice were born weighing 40% below average. It's possible that the mother's copy of Igf2 is silent because turning it off helps to slow the growth of a fetus. Mice carry another gene Igf2r which interferes with the growth-spurring activity of Igf2. This gene may have evolved to provide defense to the mother, reducing the damage to her body from excessive growth of offspring. In the case of Igf2r, it is the father's gene that is silent, perhaps as a way for fathers to speed up the growth of their offspring. If the mother's copy of Igf2r is disabled, mouse pups are born 125% heavier than average. 1.) Like mothers in other species, female mammals can maximize their lifetime fitness by moderating the amount of investment they put into individual offspring. This investment includes nutrients mothers provide to embryos through the placenta and the milk they produce after birth. If a female invests too much of these resources on one offspring, she may put her own health and future reproductive success at risk. Haig proposed that natural selection favors adaptations that let mothers rein in the nutrition they supply to their offspring. A father benefits if his mate puts lots of energy into her current pregnancy. Chances are good that her current offspring are his, but there's little guarantee that her future offspring will be his as well. So even if the mother's health is harmed, the father benefits from more energy going to his offspring. They'll be healthier as a result, and more likely to survive until adulthood.

How do inter and intra sexual selection differ from each other? How does this relate to sexual dimorphism... 1.) which type may produce ornaments in one sex? 2.) which type may produce weapons/armaments in one sex? 3.) which type may produce larger male size? 4.) which type may produce larger female size?

Intersexual selection occurs when members of the limiting sex (generally females) actively discriminate among suitors of the less limited sex (generally males). Often called female choice. Intrasexual selection occurs when members of the less limiting sex (generally males) compete with each other over reproductive access to the limiting sex (generally females). Often called male-male competition. Sexual selection: differential reproductive success resulting from competition for mates --> result: sexual dimorphism typically stronger on males: male biased OSR 1.) Ornaments: attractive traits that increase mating; exaggerated traits compared to females --> intersexual selection 2.) Armaments: weaponry/male size used to outcompete other individuals --> intrasexual selection 3.) intrasexual selection 4.) intersexual selection

How might sexual selection lead to reproductive isolation in sympatry? (consider the crickets)

Kerry Shaw studied species of swordtail crickets found only in Hawaii. The oldest lineages are found on the westernmost islands. Later the swordtail crickets hopped eastward from island to island. This pattern in similar to the origin of the islands themselves. They owe their existence to molten rock upwelling from a mantle plume beneath the floor of the Pacific Ocean. Hawaiian islands formed by plate moving over fixed hot spot. Sea mounts that form islands then erode. Swordtail crickets first colonized Hawaii's oldest islands and then expanded to the newer islands as these islands emerged from the ocean. These movements apparently have been rare because there has been no genetic evidence of crickets moving back east and interbreeding. Once the crickets came to the new island, they were isolated from populations on other islands and then diverged to the point that they no longer recognize crickets on other islands as potential mates. Speciation did not simply produce a single new species per island. When the insects arrived on a new island, they rapidly radiated into several new species. There is also a lack of evidence that the crickets have diverged ecologically. There is one striking phenotypic difference between the crickets: their courtship songs. Each species produced chirps in a distinct pattern, and the females are keenly sensitive to tiny variations in their songs. Even within species, the crickets songs have diverged along with the female preference for different songs. Using QTL analysis they found that the same locus was associated with both the male song production and the female song preference. Genetic variations cause populations to diverge in both their male songs and female preferences. These shifts rapidly introduce reproductive barriers between the populations opening the way to further speciation without any initial ecological divergence.

What does life history refer to? What basic characters are often used as a description?

Life history refers to the pattern of investment an organism makes in growth and reproduction. Life-history traits include an organism's age at first reproduction, the number and size of offspring produced, and life span.

Armor in the three-spined sticklebacks (Gasterosteus aculeatus) is controlled (in part) by the Edagene (ectodysplasin). Were mutant alleles for low Eda expression likely present before or after the introduction of the fish to freshwater lakes?

Low Eda expression was likely present before the introduction of the fish to freshwater lakes. For the first 93,000 years, there were sticklebacks with just a few small protective spines. But then this ancestral phenotype was joined by more heavily armored sticklebacks with spines that were longer and more numerous.

How does the study of the medium ground finch demonstrate that selection can vary over time?

Medium-ground finches could choose from two kinds of seeds: small seeds and hard woody seeds. In 1977, Daphne Major was hit by a major drought, leaving the medium-ground finches without any small seeds to eat. A few years later, it was discovered that the average size of their beaks was deeper. Before the drought, the population ranged in beak size from 8 to 11 mm with an average depth of 9.2 mm. After the drought, the average beak size has shifted half a millimeter to 9.7 mm, or about 15% of the range of variation. This shift occurred because finches with bigger beaks had a better chance of surviving the drought. Natural selection caused the average size of the beaks of medium-ground finches to increase within the population. 5 years later, heavy rains came to the island and gave small-beaked birds the advantage. In just a few generations, the average size of the beaks decreased by 2.5%. The pattern of selection can change over time. The Grants measured selection favoring big, deep beaks in some years and small, narrow beaks in others. Both the strength of selection, and its direction, fluctuated several times over the course of their study

What is an operational taxonomic unit? What is the threshold?

Microbiologists compared the variations in 16S rRNA genes from individual microbes that, according to the traditional methods of diagnosing a microbial species, belonged to the same species. They found that the gene varied by up to 3% between individuals. They decided that if 2 microbes were at least 97% identical in the 16S rRNA gene, they belonged to the same taxonomic group. They referred to this group as a species or sometimes as an operational taxonomic unit or OTU. By this standard, the diversity of microbes is vast. A single spoonful of soil may have 10,000 different species of bacteria. That's more species of bacteria than have been formally named and described in the history of science. If we follow the threshold of 97% sequence identity to distinguish species, likely millions- perhaps even hundreds of millions- of microbial species live on Earth. However, scientists realize that the 97% threshold has no deep biological meaning. A good example of its arbitrariness is Strep pneumoniae and S. mitis. They were identified as species before the advent of molecular biology. Microbiologists simply observed their ecological roles in our bodies and judged them to be different enough to be considered separate species. S. pneumoniae is a pathogen that can cause pneumonia by growing in our airway. S. mitis lives harmlessly on teeth. Yet the 16S rRNA sequences of these 2 'species' turn out to be over 97% identical. In fact, they're 99% identical. They should therefore be considered a single species, despite their drastic ecological differences.

Under what circumstances could miscarriage improve the fitness of a female? How is this similar to what male sand goby's do and why?

Miscarriages are sometimes the result of flexible strategies. When fertilized eggs begin to develop, they may carry harmful mutations. They are favored by natural selection because they can reduce month(s) of investment for embryos that are unlikely to survive or reproduce on their own. Spontaneous abortion may be an effective strategy for maximizing fitness by regulating parental investment, but it only works in species that control the development of their offspring inside their bodies after fertilization. The male sand goby builds a nest in an empty shell that he excavates. After successful courtship, a female goby releases her eggs, which are then fertilized by the male. Male sand gobies will sometimes dig up their nests and devour their own eggs. Selectively eating some of the eggs, the fathers were increasing the survivorship of the remaining eggs. The sand goby fathers also adjust the extent of their cannibalism to the density of eggs in their nests. The denser the eggs in a nest, the more eggs the father was likely to eat. Rather than being a random act of destruction, the cannibalism appears to be a response the males make to certain changes in their environment- cannibalism results in increasing egg survivorship.

For species that evolve armaments in one sex- how does their reproductive success vary with age?

Most males fail to breed during the beginning of their lifespan. Those that do were not able to begin breeding until they were much older and larger than females, and able to fight to the top of the pack. If they achieved this status, they could hold it for only a brief period before being killed or replaced by new males. (as seen in stags)

How did the opossums of Sapelo Island, GA demonstrate the tradeoffs between reproduction and longevity? What effect does predation have on selection for these traits?

On Sapelo Island, the lack of predators changed the extrinsic mortality rate. Since the opossums were more likely to survive older ages, individuals that invest in cell repair would be able to have more offspring throughout their life span. The Sapelo Island opossums were less likely to die than mainland opossums. As a result, the Sapelo opossums lived markedly longer on average. This was not simply due to predation: the mainland opossums deteriorated faster than the ones on the island. Along with slower aging, the Sapelo opossums produced fewer offspring in each litter, as would be expected if investment in survival mechanisms came at the expense of reproduction- that is, if there were a trade-off between survival and reproduction. Even though females on Sapelo Island produce fewer offspring in their first year than opossums on the mainland, more of these females lived to breed again in their second year. Because more opossums on Sapelo Island survived longer, a slower- yet successful- reproductive strategy evolved.

How does Hoekstra think white light fur color evolved in coastal populations? What was the agent of selection for this phenotype?

On the Gulf Coast, it turns out, these lighter coats were the results of mutations to several genes involved in the pathway for pigmentation. One mutation changed a single amino acid on the melanocortin-1 receptor (Mclr), decreasing the sensitivity of the receptor to signals that would otherwise lead to the production of dark pigmentation. A second mutation increased the expression of a gene known as Agouti, which interferes with the signaling of Mclr. Combined, these two genetic changes resulted in reduced levels of melanin synthesis and lighter overall coat color. Variation in the trait leads to differential reproduction success among individuals in a population --> how does the color of mice affect their chances of getting killed by predators? Oldfield mice live on the mainland tend to be dark matching dark soils. Beach mice live on white sand are much lighter.

How does the pan and core genome of E. coli vary? How are they changing?

Only a small fraction of the genes they find are present in every E. coli strain. The others are present in one or a few strains. Scientists refer to these genes as the 'core genome' and pan-genome.' The core genome was inherited by all the E. coli strains from their common ancestor, and the pan-genome genes were later acquired by individual lineages. If genes are moving frequently from one lineage to another, life seems to blur into a jumble of mosaic-like genomes. After the genomes of 3 strains of E. coli were sequenced scientists discovered that they share only a limited 'core' of genes. The E. coli pan-genome- the total number of genes found in all strains of E. coli- has continued to expand. But the core genome has become smaller. When a strain lacks a homologous gene found in other strains, the corresponding space is left blank. The analysis reveals that only 6% of the genes are shared by all strains.

What is parapatric speciation?

Parapatric speciation is the evolution of new species within a spatially extended population that still has some gene flow. A geographical barrier emerges that only partially isolates 2 populations. The gene flow is reduced, but not eliminated.

Considering that a parent's fitness increases as their offspring do well, why is there a parent-offspring conflict regarding care? Could you discuss examples?

Parent-offspring conflict occurs when parents benefit from withholding parental care or resources from some offspring (e.g., a current brood) and invest in other offspring (e.g., a later brood). Conflict arises because the deprived offspring would benefit more if they received the withheld care or resources. To maximize her lifetime fitness, for example, a female bird may not provide the maximum resources to earlier broods. A chick from one of those early broods might be more likely to survive to maturity if its mother did provide it with more food, but that would lower the survival rate of siblings from later broods. optimal allocation of parental effort differs depending on perspective. What's most beneficial for mom is often not the same as what's most beneficial to offspring. Chicks will put considerable energy into calling out their parents, straining their bodies, and opening their mouths wide- even putting their entire families at risk of being attacked by predators. Chicks manipulate the intensity of their begging to maximize the food they get from their parents. The intensity of begging increases as the chicks get close to fledging, for example, which is when parents are likely to benefit most if they begin to pull back on their efforts. Begging also allows chicks to compete against members of their own brood.

What species appears to be under stronger selection (brown or polar bears)? What traits are under strong selection? How does this fit with the niche of these animals?

Polar bears experienced strong selection for rapid divergence in ecological traits. Consistent with their rapid adaptation to a harsh new environment polar bears experienced stronger selection than brown bears. Polar bears specialized in catching marine mammals at sea. Many of the genes that have experienced the strongest selection in polar bears show clear links to their new ecological niche. One gene, for example, called APOB encodes a protein that binds cholesterol. Because polar bears feed on seals, their diet is rich in fatty acids, leading to high level of cholesterol in their blood. A drastic change in their APOB proteins may enable them to reduce the harm that come with such a diet, such as heart disease. There are also genes involved in heart function have evolved rapidly in polar bears. They may be under selection to cope with the polar bear diet as well or perhaps with their demanding swims through frigid water. Other rapidly evolving genes in polar bears include genes involved in pigmentation.

If fish form stable pair bonds, both helping with parental care, should protandrous or protogynous hermaphroditism be favored? Why?

Protandrous: male first sequential hermaphroditism (?). Clownfish typically only 2 fish per anemone form pair bonds. If one fish leaves/dies another individual will enter the pair. The larger one (usually the present) becomes female. Size is more important on females than males because they can produce larger eggs.

What mechanisms of evolution could lead to reproductive isolation in allopatric populations? Which mechanism of evolution is prevented in allopatry?

Reinforcement refers to the increase of reproductive isolation between populations through selection against hybrid offspring. Natural selection favors prezygotic isolation mechanisms that prevent the formation of hybrids with reduced fitness.

Why is it challenging to apply the same species concept use for eukaryotes to prokaryotes?

Scientists developed the biological species concept of a species in the light of evolution. But these concepts proved difficult to apply to microbes. Bacteria and archaea, for example, do not exist as males and females that reproduce sexually. Instead, they mainly reproduce asexually producing identical or nearly identical clones. The BSC as envisioned by Mayr has no relevance for them.

What is the closest relative of polar bears? How long ago did they diverge? Why is this thought to be an example of ecological speciation?

Scientists estimate that polar bears diverged from brown bears relatively recently- somewhere between 479,000 and 343,000 years ago. At first, the northern populations of brown bears would have survived as they had at lower latitudes feeding on land on a variety of food. But then the climate changed, replacing high artic forests with tundra and ice sheet. The northern brown bears became isolated from the brown bears and began to evolve in allopatry. Polar bears experienced strong selection for rapid divergence in ecological traits.

How common is monogamy? In mammals? In birds? How is sexual monogamy different from social monogamy?

Sexual monogamy is very rare and occurs when each male mates with a single female, and vice versa. Social monogamy occurs when a male and female form a stable pair bond and cooperate to rear the young even if either or both partners sneak extra-pair copulations. Social monogamy occurs in a few fish, insect, and mammal species, and in almost 90% of bird species.

How does the sensory bias hypothesis relate to origin of female choice for a specific character?

Some studies suggest that females have ancient preferences for certain shapes or colors, and these sensory biases trigger sexual selection in males. Female guppies prefer to mate with males with bright orange spots. Their preference may be linked to an attraction to orange-colored fruits that sometimes land in their streams. In one experiment, scientists found females with stronger preferences for orange in males would peck more at on orange fruitlike object.

How does the genetic variation of maize and teosinte compare? What caused the difference?

Teosinte was taller and broader leaved than most grasses, and people collected its seed heads for food. All modern maize appears to have descended from this original domestication event. After domesticating teosinte, farmers continued to select for advantageous traits. By 5500 years ago, cobs had already increased in the number of rows of kernels and in kernel size. Analysis of allelic diversity in these early cobs suggests that by 4400 years ago, early maize had lost almost 30% of the allelic diversity originally present in wild teosinte populations. Such loss of variation is indicative of strong selection and a genetic bottleneck as would be expected if selective harvesting entailed breeding only a small subset of the wild population.

How heritable is the beak depth in the medium ground finch (Geospiza fortis)? How is h2 calculated? is this due to VD, VA, VI, VE?

The Grants' team found that beak size is heritable. Roughly 65% of the phenotypic variance in beak length, and as much as 90% of the variance in beak depth, is attributable to additive (VA) genetic effects of alleles (h2= 0.65 and 0.90, respectively). Big-beaked birds tend to produce chicks with big beaks and small-beaked birds tend to produce chicks with small beaks. The equation R= h2 x S to find that the average beak size on Daphne Major has the potential to evolve rapidly in response to natural selection.

What is the operational sex ratio (OSR)? How is this different from the number of reproductive males and females? How does it affect sexual selection?

The OSR is the ratio of male to female individuals who are available for reproducing at any given time. If you simply tally the number of males and females, the ratio will typically be close to 1:1. But in many species, the OSR is very biased because there are so few receptive females per available male. When the OSR is strongly male biased, males may face stiff competition for the opportunity to mate with a reproductive female. This competition creates the opportunity in males for selection for traits that are primarily concerned with reproduction. This type of selection is called sexual selection. In many species, a male-biased OSR leads to sexual selection favoring males that can outcompete other males for access to females. Intrasexual selection occurs when members of the less limiting sex compete with each other for access to the limiting sex. Intersexual selection occurs when the members of the limiting sex discriminate among the potential mates from the other sex.

How do mules and hinnies demonstrate the effects of genetic imprinting?

The appearance between and donkey and hinny differs because the species that serves as the father and mother are reversed. In each species, different sets of genes are imprinted in males and females, leading to different patterns of gene expression in their hybrid offspring. Male donkey and female horse produces a mule. Female donkey and male horse produces a hinny. Genomic imprinting occurs when genes inherited from one or the other parent are silenced due to methylation. Imprinting can result in offspring who express either the maternal or paternal copy of the gene but not both.

How did Anolis caronlinensis evolve in response to the introduction of Anolis sagrei?

The behavioral shift also led to an evolutionary change in morphology. The lizards that shifted to higher in the trees evolved larger toe pads with more ridges.

Why did Melander suggest poor application of pesticides was necessary to prevent pests from evolving resistance?

The best way to keep the scales from becoming entirely resistant to pesticides was to do a bad job applying those herbicides. By allowing some susceptible scales to survive, farmers would keep the susceptible genes in the scale population.

Why would gape size of native Australian snakes decrease in response to the introduction of the cane toad?

The cane toads are strong agents of selection on their predators- native Australian snakes, overall, have become larger since cane toads were introduced. Larger body size raises the fitness of the snakes because it lowers the concentration of toxin they ingest when they attack a cane toad. Bigger snakes are thus more likely to survive a given dose of toxins. But they also found evidence that smaller gape widths evolved in the snakes. Snakes with smaller gape widths cannot swallow the biggest toads- which are also the most toxic and thus likely to kill the snakes.

How did they know gall size is controlled by the gall fly (and that this phenotype varies)?

The difference in gall size pointed to an inherited component to the variation in how the flies induced galls to form in their host plants. Galls met two of the conditions for natural selection- variation in populations and an inherited component of that variation.

How does the variation in reproductive success (number of mates etc.) relate to the strength of sexual selection?

The higher the reproductive variance, the stronger the effects of sexual selection. Strong sexual selection typically results in sexually dimorphic traits that are exaggerated, or more elaborate, in the sex with highest reproductive variance. Over their lifetime male and female elephant seals varied in their reproductive success, but this variance was much higher for males than it was for females. Such higher variance in male reproductive success generates intense sexual selection for traits that enable males to win in these contests. Sexual dimorphism- is a difference in form between males and females of a species, including color body, size, and the presence or absence of structures used in courtship displays or in contests.

How is the phylogenetic species concept different from the biological species concept? 1.) Which one focuses more on the mechanism of isolation? 2.) Which one focuses more on the uniqueness of species? 3.) Which one would be more easily applied to species that reproduce asexually? How about fossil species?

The phylogenetic species concept is the idea that species are the smallest possible groups whose members are descended from a common ancestor and who all possess defining or derived characteristics that distinguish them from other such groups. The biological species concept is the idea that species are groups of actually (or potentially) interbreeding natural populations that are reproductively isolated from other such groups. 1.) Biological species concept 2.) Phylogenetic species concept 3.) Phylogenetic species concept (?)

Can you think of examples where natural selection did the same thing more than once (in different populations)? (consider the oldfield mice and 3-spined stickleback fish)

The sticklebacks that remained in the lakes founded resident populations and could no longer return to the ocean. In each of these lakes, the isolated sticklebacks experienced a new set of selection pressures. The lake sticklebacks are measurably different from marine populations including body size and shape, head shape, the size of fins, number of teeth, and armor. Marine sticklebacks grow spines and bony plates that protect them from predators. Sticklebacks in freshwater lakes have fewer spines and drastically reduced lateral plating compared to their closest marine relatives. Lakes have fewer predators, and without predatory fish in the lakes, growing armor no longer benefits the fish. It's very expensive to produce armor in lakes because freshwater has low concentrations of the ions necessary for bone growth. Fish with low-Eda alleles have an advantage in freshwater. They grow to be larger as juveniles, have higher overwinter survival, and begin breeding sooner than fish that have the "complete armor" version of the Eda allele.

What is two-fold cost of sex? What other disadvantage of sexual reproduction can you think of?

The two-fold cost of sex refers to the disadvantage of being a sexual rather than an asexual organism. Asexual lineages have an intrinsic capacity to grow more rapidly in each generation because all progeny can produce offspring. In sexual populations, males cannot produce offspring. This limitation effectively halves the rate of replication of sexual species. Search cost: males and females must locate each other in order to mate. This can involve time, energy, and risk of predation. Reduced relatedness: Sexually reproducing organisms pass only half of their alleles to their offspring because meiosis generates gametes that are haploid. This halves the relatedness between parents and their progeny. Risk of sexually transmitted diseases: mating between males and females provides an effective means of transmission for many pathogens. Asexual populations do not mate and so avoid this risk.

Why is the low Eda allele advantageous in freshwater environments? What tradeoffs are involved?

They grow to be larger as juveniles, have higher overwinter survival, and begin breeding sooner than fish that have the "complete armor" version of the Eda allele. Production of armor energetically costly Little predation pressure to counterbalance

If the low Eda allele is not advantageous in the marine environment, how could it persist in marine populations?

This allele is recessive, and it lingered in marine sticklebacks populations at low frequency until some fishes colonized freshwater habitats. When recessive alleles are rare in a population, they are largely invisible to selection, enabling them to persist for a very long time. Once the sticklebacks were in the new habitat, the allele was favored strongly by natural selection, leading to parallel evolution of reduced armor in lake after lake.

Before the drought on Daphne Major, the average beak depth of the population was 9.2 mm, after the drought, it was 9.7 mm. Does this difference refer to R, h2, or S? How would each of these (R, h2, or S) be calculated?

This difference refers to the selection coefficient (S) R= h2 x S h2= R/S S= R/h2

Assume female mice have a preference for brighter red color. How could this preference exist... and males not have this color? What could counteract it?

This preference could be because of they think this trait is the highest-quality, healthiest individuals from the rest of the lot. (or pre-existing sensory bias). Counteract?

What advantage does Muller's ratchet refer to?

When asexual organisms acquire deleterious mutations that offset earlier, beneficial mutations, the two types of mutations can't be separated. The bad mutations continue to accumulate (through a process called Muller's ratchet), and the burden that these mutations place on the fitness of individuals (their genetic load) gradually increases. Sexual reproduction can remove harmful alleles.-->Clearance of deleterious mutations

How have pesticides affected herbivorous insects? Are pesticides effective?

When farmers apply a new chemical pesticide to a field, they kill a large proportion of its vulnerable population of pests. This die-off produces strong selection on the insect. Individual insects with mutations for biochemical mechanisms enabling them to survive. These survivors now have more food to eat, boosting their survival and fecundity. As they propagate themselves, they populate subsequent generations of the pest population with offspring who are also resistant to the pesticide, and alleles conferring resistance spread. The large size of insect populations can produce substantial genetic variation. When the intense selection of pesticides is applied to the insects, resistance can evolve rapidly. It takes only a few years for resistance to a new pesticide to emerge.

Although there are exceptions... how do males and females generally vary in what limits their reproductive success?

When males experience a greater opportunity for sexual selection than females (higher variance in reproductive success), sexual selection is likely to be stronger in males than in females. For example, peacocks do not help peahens with parental care, and some of the males have much more reproductive success than others. In such a case, elaborate male traits may evolve. When males contribute to offspring care, the variance in reproductive success will be more similar for males and females and extreme sexual dimorphism is not expected. In many seabird species, males and females are monogamous and raise their chicks together. Not surprisingly, the males and females of many of these species are practically indistinguishable. When males provide all the parental care, the variance in reproductive success will be higher in females. As a result, sexual selection can be stronger in females than in males, females compete for access to males who provide all the parental care. Females are larger, brighter, and more aggressive than males.

What traditional crops (food items you find in a store) have been artificially selected from wild cabbage? Could you identify those that were selected for characters of the flower shoots, leaves, stems, buds?

Wild cabbage was selected for its leaves (cabbage, kale), stems (kohlrabi), flower shoots (broccoli, cauliflower), and buds (brussels sprouts)

How are bacteria species typically defined (traditionally before molecular data)?

With the advent of molecular biology, microbiologists began to rely on a phylogenetic species concept. One widespread method involves examining a gene for a ribosomal RNA molecule called 16s rRNA. This gene, which is found throughout the tree of life, evolves slowly enough that it is phylogenetically informative even when scientists are comparing lineages that descend from a common ancestor that lived billions of years ago. (?)