Chapter 24 reproduction of animals

Habitat isolation

When two species encounter each other only rarely. (example: North American maggot fly. One lives in apple and others live in the hawthorn fruit).

Which information is relevant to the biological species definition? A. Hawthorn and apple maggot flies are physically indistinguishable. B. Hawthorn and apple maggot flies are genetically distinguishable and have a distinct genetic profiles. C. There is a 4-6% hybridization rate between hawthorn and apple maggot flies. D. Hawthorn and apple maggot flies strongly prefer to mate and lay fertilized eggs in hawthorns and apples, respectively.

Which information is relevant to the biological species definition? A. Hawthorn and apple maggot flies are physically indistinguishable. B. Hawthorn and apple maggot flies are genetically distinguishable and have a distinct genetic profiles. C. There is a 4-6% hybridization rate between hawthorn and apple maggot flies. D. Hawthorn and apple maggot flies strongly prefer to mate and lay fertilized eggs in hawthorns and apples, respectively. C there is a 4-6% hybridization rate between hawthorn and apple maggot flies.

Which information is relevant to the ecological species definition? A. Hawthorn and apple maggot flies are physically indistinguishable. B. There is a 4-6% hybridization rate between hawthorn and apple maggot flies. C. Hawthorn and apple maggot flies are genetically distinguishable and have a distinct genetic profiles. D. Hawthorn and apple maggot flies strongly prefer to mate and lay fertilized eggs in hawthorns and apples, respectively

Which information is relevant to the ecological species definition? A. Hawthorn and apple maggot flies are physically indistinguishable. B. There is a 4-6% hybridization rate between hawthorn and apple maggot flies. C. Hawthorn and apple maggot flies are genetically distinguishable and have a distinct genetic profiles. D. Hawthorn and apple maggot flies strongly prefer to mate and lay fertilized eggs in hawthorns and apples, respectively D Hawthorn and apple maggot flies strongly prefer to mate and lay fertilized eggs in hawthorns and apples, respectively

Which information is relevant to the phylogenetic species definition? A. Hawthorn and apple maggot flies are physically indistinguishable. B. There is a 4-6% hybridization rate between hawthorn and apple maggot flies. C. Hawthorn and apple maggot flies are genetically distinguishable and have a distinct genetic profiles. D. Hawthorn and apple maggot flies strongly prefer to mate and lay fertilized eggs in hawthorns and apples, respectively

Which information is relevant to the phylogenetic species definition? A. Hawthorn and apple maggot flies are physically indistinguishable. B. There is a 4-6% hybridization rate between hawthorn and apple maggot flies. C. Hawthorn and apple maggot flies are genetically distinguishable and have a distinct genetic profiles. D. Hawthorn and apple maggot flies strongly prefer to mate and lay fertilized eggs in hawthorns and apples, respectively C Hawthorn and apple maggot flies are genetically distinguishable and have a distinct genetic profiles.

Temporal Isolation

form of reproductive isolation in which two populations reproduce at different times (example: the blue-footed booby. Also different species of spotted skunks do not mate because one species breeds during Winter and the other breeds during Summer)

(a) Which species concept(s) could you apply to both asexual and sexual species? (b) Which would be most useful for identifying species in the field? Explain

(a) All of the species concepts can be applied to both sexual and asexual species because they define species on the basis of characteristics other than ability to reproduce. In contrast the species concepts can only be applied to species which reproduce. (b) morphological species concept because it is based on appearance of the organism.

Consider two species that diverged while geographically separated but resumed contact before reproductive isolation was complete. Predict what would happen over time if the two species mated indiscriminately and (a.) hybrid offspring survived and reproduced more poorly than offspring from intraspecific mating's or (b.) hybrid offspring survived and reproduced as well as offspring from intraspecific mating's.

(a): If hybrids consistently survive and reproduce poorly compared to the offspring of intraspecific mating's, it's possible that reinforcement would occur. If it did, natural selection would cause prezygotic barriers to reproduction between the parent species to strengthen over time, decreasing the production of unfit hybrids and leading to a completion of the speciation process. (b): If hybrid offspring survive and reproduce as well as the offspring of intraspecific mating's, indiscriminate mating between the parent species would lead to the production of large numbers of hybrid offspring. As these hybrids mated with each other and with members of both parent species, the gene pools of the parent species could fuse over time, reversing the speciation process.

Sexual selection

1. 600 species of cichlids in Lake Victoria in East Africa. Why? 2. Sexual selection for mates of different colors has likely contributed to speciation in cichlid fish in Lake Victoria.

Morphological species concept

1. A species is a set of individuals with morphological features in common. 2. Key aspect is the MORPHOLOGY of members of a species. 3. Individuals of a species are morphologically similar to one another, yet morphologically distinct from individuals from another species

Phylogenetic species concept

1. A species may be defined by its unique genetic history as a tip of a phylogenetic tree. 2. Species are defined by their UNIQUE DERIVED FEATURES and SHARED ANCESTRY.

Habitat differentiation

1. Appearance of new ecological niches 2. Examples: North American maggot fly.

Apples (case study)

1. Apples were introduced to North America in 1600s. 2. Most widely grown fruit in North America.

Limitations of the Biological species concept

1. Cannot be applied to fossils or asexual organisms (including all prokaryotes) 2. Emphasizes absence of gene flow 3. Grizzly bears and polar bears can mate to produce "grolar bears"

Hawthorn maggot fly life cycle (Rhagoletis pomonella) (case study)

1. Female lays fertilized eggs in fruit. 2. Maggots (larvae) emerge from egg, feed on fruit, and grow through several molts. 3. Healthy maggots drop from tree with fruit and burrow in soil. 4. Pupation takes place in soil. 5. Adult maggot flies emerge from soil and fly to fruit trees, where they mate on surface of fruit.

Frequency-dependent selection

1. Fitness of a phenotype depends on how common it is in population 2. Example: "right-mouthed" and "left-mouthed" scale-eating fish. 3. Trait determined by two alleles. 4. For scale-eating fish (never need to know genus and species) when one phenotype is at a high frequency there is high competition for that side of the fish and there is less competition on the other side thus favoring the phenotype that is in the minority so it has a higher fitness. Thus flipping back and forth between left-mouthed and right-mouthed for scale-eating fish.

Factors causing genetic divergence between isolated populations

1. Founder effect 2. Mutation 3. Genetic drift 4. Differential selection

Stability

1. HIGH GENE FLOW flow into hybrid zone from parent zones->overwhelms reproductive barriers 2. Stable hybrid zone 3. Hybrids can have reduced fitness 4. Example is Bombina toads.

Prezygotic barriers

1. Habitat isolation 2. Temporal isolation 3. Behavioral isolation 4. Mechanical isolation 5. Gametic isolation

Today: There are Hawthorn & Apple Maggot Flies (case study)

1. Hawthorn and apple maggot flies are physically indistinguishable. a. Genetically distinct, with different genetic profiles. 2. No geographic isolation or physical separation between hawthorn and apple maggot flies

Hawthorn trees and hawthorn maggot fly (case study)

1. Hawthorn trees are native to North America. 2. Hawthorn fruit is eaten by larvae of hawthorn maggot fly.

Hawthorns (case study)

1. Hawthorns are native North American scrubs. 2. Hawthorn fruits are small.

Heterozygote advantage

1. Heterozygote advantage occurs when heterozygotes have a higher fitness than both homozygotes. 2. Can result from stabilizing or directional selection. 3. Sickle cell disease and malaria. 4. The heterozygote version of hemoglobin gives mild anemia and is resistant to malaria.

Hybrid zones reveal factors that cause reproductive isolation

1. Hybrid zone 2. Two species of toad in genus Bombina interbred a. Zone narrow. b. High elevation (yellow-bellied toad) c. Low elevation (fire-bellied toad) 3. Hybrids often have reduced fitness compared with parent species

Fusion

1. Hybrids as fit as parental. 2. High gene flow. 3. Undoes speciation->one speciation

Reinforcement

1. Hybrids have reduced fitness viability 2. Prezygotic barriers 3. Reinforces speciation 3. Hybrid one disappears in time.

sympatric speciation

1. In sympatric speciation, there is no geographic barrier to gene flow. 2. What prevents reproduction between individuals from different populations living in the same area? a. Gene flow in sympatry may be prevented by polyploidy (especially in plants) or by habitat specialization. b. These factors may also be important in allopatric speciation c. sexual selection d. Polyploidy e. Habitat differentiation •New species arises within the range of the parent species (reproductive isolation without geographic separation) •Change in ploidy (chromosome sets) •An autopolyploid is an individual with more than two chromosome sets, derived from one species •An allopolyploid is a species with multiple sets of chromosomes derived from different species -Allopolyploidy - formation of a viable interspecific hybrid coupled with nondisjunction and polyploidy to form a new species -Up to 80% of plant species are polyploid (most allopolyploid) - wheat, oats, cotton, potato, tobacco, etc

Apple vs. Hawthorn: the maggot's viewpoint (case study)

1. Large apple fruit provides 220 times more food than hawthorn fruit. 2. Nutritional quality of hawthorn fruit is superior 3. 52% of hawthorn maggots survive vs. 27% of apple maggots.

Hawthorn and apple maggot flies (case study)

1. Maggot flies tend to mate with their own kind. 2. Hawthorn maggot flies strongly prefer to mate on and lay fertilized eggs in hawthorn fruit. 3. Apple maggot flies strongly prefer to mate on and lay fertilized eggs in apple fruit. 4. There is only a 4-6% hybridization rate between hawthorn and apple maggot flies.

Polyploidy

1. Presence of extra sets of chromosomes 2. More common in plants than in animals. 3. New biological species in sympatry within a single generation. 4. AUTOPOLYPOIDY VS. ALLOPOLYPLOIDY 5. Many important crops (oats, cotton, potatoes, tobacco, and wheat) are polyploids 6. Can be created in lab

Reproductive isolation by ecology and behavior

1. Prezygotic mechanism 2. Postzygotic mechanism

Postzygotic barriers

1. Reduced hybrid viability 2. Reduced hybrid fertility 3. Hybrid breakdown

Hybrid zones over time

1. Reinforcement 2. Fusion 3. Stability

Speciation and reproductive isolation

1. Reproductive isolation a. Barriers can be prezygotic or postzygotic 2. Is called a hybrid if a new species is made between species.

Gene flow between two guenon monkeys in Gombe National Park

1. Speciation occur in sympatry or allopatry? sympatry because it is behavioral.

Ecological species concept

1. Species is a set of organisms that exploit a single NICHE. 2. Key aspects are RESOURCES exploited and HABITAT occupied by members of a species 3. Emphasizes the role of disruptive selection

Speciation rates

1. Studied using fossil record, morphological data, or molecular data

Change in environmental conditions can result in relocation of existing hybrid zones or production of novel hybrid zones. Why?

1. change in environmental conditions can result in the relocation of existing hybrid zones or production of novel ones 2. breeding between hybrid and parent species can result in transfer of alleles from one parent to another 3. the transfer of novel alleles may help parent species cope with changing environments

What is the biological basis for assigning all human populations to a single species? Are humans still evolving? Can you think of a scenario where a second human species could originate in the future?

1. the human species is still evolving but humans (ourselves) depending on the age, are not still evolving today. 2. Another scenario where a second species could originate in the future would be if a huge environmental change were to wipe off the entire human species and God were to make humans, just like he did with Adam and Eve, and repopulate the Earth again.

phylogenetic tree

A family tree that shows the evolutionary relationships thought to exist among groups of organisms

Hybrid zone

A hybrid zone is a narrow geographic region where two genetically distinct populations or species are found in close proximity and hybridize to produce offspring of mixed ancestry. Hybrid zones are widespread, both geographically and across animal and plant taxa.

Define biological species concept

A species a group of populations that are able to interbred and produce viable, fertile offspring.

Define morphical species concept

A species is a group of individuals in population that look the same.

Define ecological species concept

A species is a group of individuals that are defined by by sharing their niche in an environment.

Define phylogenetic species concept

A species is a group of individuals that share unique derived features and ancestry.

Plant species A has a diploid number of 12. Plant species B has a diploid number of 16. A new species, C, arises as an allopolyploid from A and B. The diploid number for species C would probably be

A) 12. B) 14. C) 16. D) 28. E) 56. d 28

Which of the following factors would not contribute to allopatric speciation?

A) A population becomes geographically isolated from the parent population. B) The separated population is small, and genetic drift occurs. C) The isolated population is exposed to different selection pressures than the ancestral population. D) Different mutations begin to distinguish the gene pools of the separated populations. E) Gene flow between the two populations is extensive. e Gene flow between the two populations is extensive.

Bird guides once listed the myrtle warbler and Audubonʹs warbler as distinct species. Recently, these birds have been classified as eastern and western forms of a single species, the yellow rumped warbler. Which of the following pieces of evidence, if true, would be cause for this reclassification?

A) The two forms interbreed often in nature, and their offspring have good survival and reproduction. B) The two forms live in similar habitats. C) The two forms have many genes in common. D) The two forms have similar food requirements. E) The two forms are very similar in coloration. a The two forms interbreed often in nature, and their offspring have good survival and reproduction.

Males of different species of the fruit fly Drosophila that live in the same parts of the Hawaiian islands have different elaborate courtship rituals that involve fighting other males and stylized movements that attract females. What type of reproductive isolation does this represent?

A) habitat isolation B) temporal isolation C) behavioral isolation D) gametic isolation E) postzygotic barriers c behavioral isolation

According to the punctuated equilibria model,

A) natural selection is unimportant as a mechanism of evolution. B) given enough time, most existing species will branch gradually into new species. C) most new species accumulate their unique features relatively rapidly as they come into existence, then change little for the rest of their duration as a species. D) most evolution occurs in sympatric populations. E) speciation is usually due to a single mutation. c most new species accumulate their unique features relatively rapidly as they come into existence, then change little for the rest of their duration as a species.

The largest unit within which gene flow can readily occur is a

A) population. B) species. C) genus. D) hybrid. E) phylum. b species

What reproductive barrier limits interbreeding between hawthorn and apple maggot flies? A. Mechanical isolation B. Habitat isolation C. Temporal isolation D. Hybrid breakdown

A. Mechanical isolation B. Habitat isolation C. Temporal isolation D. Hybrid breakdown B Habitat isolation C Temporal isolation

According to the biological species concept, are hawthorn and apple maggot flies separate species?

According to the biological species concept, are hawthorn and apple maggot flies separate species? No

According to the ecological species concept, are hawthorn and apple maggot flies separate species?

According to the ecological species concept, are hawthorn and apple maggot flies separate species? Yes

According to the morphological species concept, are hawthorn and apple maggot flies separate species?

According to the morphological species concept, are hawthorn and apple maggot flies separate species?

According to the phylogenetic species concept, are hawthorn and apple maggot flies separate species?

According to the phylogenetic species concept, are hawthorn and apple maggot flies separate species? I cannot tell from the information provided

Advantages and drawbacks of ecological species concept**

Advantages: Acknowledges the role the environment plays in controlling morphological development. Disadvantages: Can miss cryptic species. Niches tend to be assumed and are difficult to define completely. Many taxa exploit overlapping resources, or can suddenly switch if a resource becomes scare. This is not a very robust species concept.

Advantages and drawbacks of morphical species concept*8

Advantages: Simple concept, most widely used particularly for plants. Disadvantages: Too much decisions on how much difference between individual is too much variation. Almost all populations are made up of non-identical individuals. They can look similar to each other but they are very different. Convergent evolution

Advantages and drawbacks of biological species concept**

Advantages: Widely used by scientists Disadvantages: Cannot be applied in all cases. Ex: Two populations never have a chance to interbreed, organisms that reproduce asexually.

Advantages and drawbacks of phylogenetic species concept***

Advantages: can be applied to extinct species. Considers information about relationships among organisms learned from DNA analysis. Disadvantages: Evolutionary histories are not known for all species.

Difference between allopatric speciation and sympatric speciation

Allopatric speciation occurs when two species are living in separate environments and therefore there is no gene flow between the populations. This will then cause the populations to differentiate (change) because they will become adapted to the different environments and niches they are living in. Sympatric speciation occurs when two species are living in the same environment. This speciation is a little more difficult to understand because the species have the occupy the same niche, however it may come down to some barriers (pre-zygotic or post-zygotic) that prevent gene flow, for example mating at different times of the day.

Is allopatric speciation more likely to occur on an island close to a mainland or on a more isolated island of the same size? Explain your prediction.

Allopatric speciation would be less likely to occur on a nearby island than on an isolated island of the same size. The reason we expect this result is that continued gene flow between mainland populations and those on a nearby island reduces the chance that enough genetic divergence will take place for allopatric speciation to occur.

Niche

An organism's role in an environment. How it affects and is affected by its environment.

prezygotic barriers

Barriers that impede mating or hinder fertilization.

Based on the information provided in this case study, are hawthorn and apple maggot flies separate species?

Based on the information provided in this case study, are hawthorn and apple maggot flies separate species? It depends on how the terms "species" is defined

Suppose you are studying two bird species that live in a forest and are not known to interbreed. One species feeds and mates in the treetops and the other on the ground. But in captivity, the birds can interbreed and produce viable, fertile offspring. What type of reproductive barrier most likely keeps these species separate in nature? Explain. (Concept Check 24.1)

Because these birds live in fairly similar environments and can breed successfully in captivity, the reproductive barrier in nature is probably prezygotic; given the species differences in habitat preference, this barrier could result from habitat isolation.

what does biological species concept emphasize?

Biological species concept emphasizes reproductive isolation

Macroevolution

Broad patterns of evolutionary change above species level

Which information is relevant to the morphological species definition? A. Hawthorn and apple maggot flies are physically indistinguishable. B. There is a 4-6% hybridization rate between hawthorn and apple maggot flies. C. Hawthorn and apple maggot flies are genetically distinguishable and have a distinct genetic profiles. D. Hawthorn and apple maggot flies strongly prefer to mate and lay fertilized eggs in hawthorns and apples, respectively.

CQ#9: Which information is relevant to the morphological species definition? A. Hawthorn and apple maggot flies are physically indistinguishable. B. There is a 4-6% hybridization rate between hawthorn and apple maggot flies. C. Hawthorn and apple maggot flies are genetically distinguishable and have a distinct genetic profiles. D. Hawthorn and apple maggot flies strongly prefer to mate and lay fertilized eggs in hawthorns and apples, respectively. A Hawthorn and apple maggot flies are physically indistinguishable.

Microevolution

Change in allele frequencies in a population over time (generations).

Timing of host fruit ripening (case study)

Different ripening time of host fruit leads to temporal separation of apple and hawthorn flies.

Behavioral isolation

Form of reproductive isolation in which two populations have differences in courtship rituals or other types of behavior that prevent them from interbreeding (example: the blue-footed boobies bird. Blue-footed only likes blue-footed. Red-footed only likes red-footed. The Blue Footed Booby only mates after a courtship display that is unique to the species)

Describe the two mechanisms that can decreases gene flow in sympatric populations, thereby making sympatric speciation more likely to occur.

Gene flow between subsets of a population that live in the same area can be reduced in a variety of ways. In some species, especially plants, changes in chromosome number can block gene flow and establish reproductive isolation in a single generation. Gene flow can also be reduced in sympatric population by habitat differentiation and sexual selection.

3. At what point is it reasonable to say that speciation has occurred?

Gene pool changes establish reproductive barriers between two populations. When there hybridization rate is low. Fully divergent, they do not produce any more hybrids.

Genetic divergence

Genetic divergence is the accumulation of genetic differences between two populations.

Biological species concept

Group of populations whose members have potential to interbreed in nature and produce viable, fertile offspring 1. Emphasizes reproductive isolation 2. Use morphology, physiology, biochemistry, and DNA sequences when grouping organisms 3. Gene flow between populations holds a species together genetically

Reproductive isolation

How do two similar species maintain genetic isolation if they come (or remain) in contact with each other)? Reproductive isolation by ecology and behavior

What are hybrid zones, and why can they be viewed as "natural laboratories" in which to study speciation?

Hybrid zones are regions in which members of different species meet and mate, producing some offspring of mixed ancestry. Such regions can be viewed as "natural laboratories" in which to study speciation because scientists can directly ob- serve factors that cause (or fail to cause) reproductive isolation.

What do hybrid zones reveal?

Hybrid zones reveal factors that cause reproductive isolation

Would you expect natural selection to favor pre-zygotic or post-zygotic isolating mechanisms between sympatric species?

I would expect natural to favor pre-zygotic isolating mechanisms because it is between sympatric species because it stops a viable offspring from being born whereas post-zygotic you can still have a hybrid that is still viable. Pre-zygotic is much stronger in stopping that from happening

Describe how an error during meiosis could lead to polyploidy.

If all of the homologs failed to separate during anaphase I of meiosis, some gametes would end up with an extra set of chromosomes and others would end up with no chromosomes. If a gamete with an extra set of chromosomes fused with a normal gamete, a triploid would result; if two gametes with an extra set of chromosomes fused with each other, a tetraploid would result.

Summarize key differences between allopatric and sympatric speciation. Which type of speciation is more common, and why?

In allopatric speciation, a new species forms while in geographic isolation from its parent species; in sympatric speciation, a new species forms in the absence of geographic isolation. Geographic isolation greatly reduces gene flow between populations, whereas ongoing gene flow is more likely in sympatry. As a result, sympatric speciation is less common than allopatric speciation.

Autopolyploidy

Individual has 2+ sets of chromosomes from same species. (example: If a tetraploid (4N) is reproductively isolated from diploids but can reproduce with other tetraploids

Allopolyploidy

Individuals has 2+ sets of chromosomes from different species. Can reproduce sexually and offspring can reproduce sexually.

Summarize evidence that the yup locus acts as a prezygotic barrier to reproduction in two species of monkey flowers. Do these results demonstrate that the yup locus alone controls barriers to reproduction between these species? Explain.

Investigators transferred alleles at the yup locus (which influences flower color) from each parent species to the other. M. lewisii plants with a M. cardinalis yup allele received many more visits from hummingbirds than usual; hummingbirds usually pollinate M. cardinalis but avoid M. lewisii plants. Similarly, M. cardinalis plants with an M. lewisii yup allele received many more visits from bumblebees than usual; bumblebees usually pollinate M. lewisii and avoid M. cardinalis. Thus, alleles at the yup locus can influence pollinator choice, which in these species provides the primary barrier to interspecific mating. Never the less, the experiment does not prove that the yup locus alone controls barriers to reproduction between M. lewisii and M. cardinalis; other genes might enhance the effect of the yup locus (by modifying flower color) or cause entirely different barriers to reproduction (for example, gametic isolation or a postzygotic barrier).

How does diploidy maintain genetic variation?

It allows recessive alleles that may not be favored in the current environment to be preserved in the gene pool by propagation in heterozygotes.

1. Are apple and hawthorn maggot flies separate species?

It depend on the species concept you use.

Mechanical isolation

Morphological differences prevent fertilization. (example: many insects cannot mate because their sex organs do not fit together, which prevents the transfer of sperm) (example: chihuahua and big dog)

There are parasites (case study)

Parasitoid wasps try to lay eggs in maggot's body, paralyzing and ultimately killing maggot. So wasps lays eggs in maggot thus paralyzing it and baby wasps eat the maggot.

allopatric speciation

Physical separation of two populations=interruption of gene flow. •Geological processes create a physical barrier that separates and isolates populations of the same species (reproductive isolation due to geographic separation) -Emergence of a mountain range -Advance or retreat of a glacier -Advance or retreat of a lake - pupfish -Emergence of an island

When a male donkey mates with a female horse, the hybrid offspring is an infertile mule. The reproductive barrier is:

Postzygotic

Hybrid breakdown

Postzygotic Barrier. Hybrid is fertile, but when they breed the next generation is sterile.

Reduced hybrid fertility

Postzygotic Barrier. Sterile hybrids due to uneven chromosome number.

Reduced hybrid viability

Postzygotic Barrier. When the genes of different species interact and impair hybrid development.

Prezygotic mechanisms

Prevent mating or fertilization

Postzygotic mechanisms

Prevent zygote development or reproduction.

The antennae of male moths can only detect sex pheromones released by a female in his species. The reproductive barrier is:

Prezygotic

Habitat isolation and temporal isolation are:

Prezygotic reproductive barriers

Does this graph indicate the gene flow is spreading fired-bellied toad alleles into the range of yellow-bellied toads? Explain.

Shows that there is gene flow but it is low because hybrids have low fitness.

Does speciation happen fast or slow?

Speciation can occur rapidly or slowly and can result from changes in few or many genes

Speciation can only be observed over millions of years. True or false?

Speciation can only be observed over millions of years. True

Speciation can only be observed over millions of years:

Speciation can only be observed over millions of years: False

Can speciation take place with geographic separation?

Speciation can take place with or without geographic separation

What does speciation do?

Speciation forms bridge between microevolution and macroevolution

Species are going extinct, but no new species are forming on Earth. True of false?

Species are going extinct, but no new species are forming on Earth. False.

Species are going extinct, but no new species are forming on Earth:

Species are going extinct, but no new species are forming on Earth: False

Gametic isolation

Sperm of one species may not be able to fertilize eggs of another species (example: in some different species of fish, reproduction is prevented because the sperm cannot penetrate the egg)

Speciation in North American maggot fly (Rhagoletis) is:

Sympatric

Speciation can occur rapidly between diverging populations, yet the time between speciation events is often more than a million years. Explain this apparent contradiction.

The time between speciation events includes the length of time that it takes for population of a newly formed species to begin diverging reproductively from one another. The time it takes for speciation to be complete once this divergence begins.

Hawthorn maggot fly Host Shift (case study)

When apples were introduced to North America, larva of hawthorn maggot fly started feeding on them instead of hawthorn tree. Switched from hawthorn since fruits were small to apples which were bigger than hawthorn fruits. Thus host shift.

Balancing selection

When natural selection maintains stable frequencies of two or more phenotypic forms in a population 1. How does diploidy maintain genetic variation? It allows recessive alleles that may not be favored in the current environment to be preserved in the gene pool by propagation in heterozygotes. 2. Includes: a. Frequency-dependent selection b. Heterozygote advantage

Three outcomes

With renewed or continued contact between two populations, there are three possible outcomes: 1. Individuals can hybridize readily->no speciation 2. Individuals do not hybridize at all->full speciation 3. Individuals hybridize but offspring have reduced fitness->Speciation in progress. Selection for evolution of strong reproductive barriers.

2. Are they in the process of speciating?

Yes, because a species is always in the process of speciating.

Postzygotic barrier

a reproductive barrier that prevents hybrid zygotes produced by two different species from developing into viable, fertile adults

Differential selection

occurs when selected participants have different characteristics for the various treatment groups, producing nonequivalent groups

Morphology

study of form

Habitat

where an organism lives

Punctuated Equilibrium

•1972 Stephen Jay Gould and Niles Eldridge suggest that evolution proceeds in spurts •Long periods of stasis in between spurts •Environmental change associated with rapid genetic changes •Explains absence of transitional fossils in many cases