Ecology and Evolution Exam 2: Chapters 6-7, 10-11
Arbitrary Choice ("Fisher's Positive Feedback Cycle")
Certain male traits are advantageous not because they indicate good quality, but simply 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 reproductive advantages of having the trait
Broad sense heritability
(H^2) is the proportion of the total phenotypic variance of a trait that is attributable to genetic variance, where genetic variance is represented in its entirety as a single value (that is, genetic variance is not broken down into different components). H^2=VG/VP +VG/VG+VE
Operational sex ratio
(OSR) is the ratio of male to female individuals who are available for reproducing at any given time.
Narrow sense heritability
(ℎ^2) is the proportion of the total phenotypic variance of a trait attributable to the additive effects of alleles (the additive genetic variance). This is the component of variance that causes offspring to resemble their parents, and it causes populations to evolve predictably in response to selection. h^2=VA/VP=VA/VG+VE=VA/VA+VD+VI+VE
Example of good genes
Females choose mates by assessing a trait that directly reflects the genetic quality of the male, and their offspring's chances of reproducing increase because they inherited his genes
example of fishers runaway
Females find an arbitrary male trait attractive and drive the evolution of increasingly extreme versions of the trait by producing sons with the attractive trait and daughters that prefer the trait
Breeder's equation
R=h^2S
Opportunity for selection
refers to the variance in fitness within a population. When there is no variance in fitness, there can be no selection; when there is large variance in fitness, there is a great opportunity for selection. In this sense, the opportunity for selection constrains the intensity of selection that is possible.
phenotypic plasticity
shaped by the interaction of these alleles with the environment
_________ can result when 2 agents of selection act in opposing directions
stabilizing selection
Physical linkage
the adjacency of two or more loci on the same chromosome.
Certainty of paternity
the probability that a male is the genetic sire of the offspring his mate produces.
Heritability
the proportion of phenotypic variance due to genetic differences
Quantitative genetics
the study of continuous phenotypic traits and their underlying evolutionary mechanisms.
Disadvantages of Sex
twofold cost of sex, search cost, reduced relatedness, risk of sexually transmitted infections
Evolution and selection are not the same
Selection can occur without evolution if heritability=0
indirect benefit
a benefit that affects the genetic quality of a particular female's offspring, such as male offspring that are more desirable to females.
Sexual dimorphism
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 (elaborate tail plumes, ornaments, pigmented skin patches) or in contests (antlers, tusks, spurs, horns).
Ansigomy
a form of sexual reproduction that involves the union or fusion of two gametes that differ in size and/or form. The smaller gamete is male, a sperm cell, whereas the larger gamete is female, typically an egg cell.
supergene
a group of functionally related genes located close enough together that they segregate as a single unit.
Monogamy
a mating system in which one male pairs with one female.
Polyandry
a mating system where females mate (or attempt to mate) with multiple males.
Selection differential (S)
a measure of the strength of phenotypic selection. describes the difference between the mean of the reproducing members of the population that contribute offspring to the next generation and the mean of all members of a population.
Parthenogenesis
a mode of reproduction in which female sex cells undergo meiosis but are not fertilized by sperm; in parthenogenetic species, females produce only daughters.
SNP (single nucleotide polymorphism)
a polymorphism that substitutes one base pair for another
Variance
a statistical measure of the dispersion of trait values about their mean.
Quantitative trait locus (QTL)
a stretch of DNA that is correlated with variation in a phenotypic trait. These regions contain genes, or are linked to genes, that contribute to popula-tion differences in a phenotype.
extended phenotype
a structure constructed by an organism that can influence its performance or success. Although it is not part of the organism itself, its properties nevertheless reflect the genotype of each individual. Animal examples include the nests constructed by birds and the galls of flies
The effect of natural selection can change in response to
climate change
The Red Queen effect describes the _____ of two species. In the case of a host and parasite, the Red Queen effect describes the _____ adaptations of a parasite to evade a host's defenses and of the host to evade a parasite's invasion. The Red Queen effect illuminates a possible benefit of ______ reproduction, which is common among organisms despite being costly. _____ allows organisms to adapt rapidly to detrimental conditions. Sexual reproduction is the most efficient means to increase the genetic ______ required for organisms to evolve rapidly. In contrast, _____ results in the least amount of genetic variation and impedes adaptation within populations.
coevolution, reciprocal, sexual, Genetic recombination, variation, asexual reproduction
However, even genes that are close together experience some _____, resulting in the _____ of linkage over time.
crossing over, loss
When mice colonized coastal habitats, _____ was still favored, but colors conferring the best crypsis ____________
cryptic coloration, shifted to pale phenotypes
epistasis
depend on nonadditive interactions between alleles at those loci
Red Queen effect
describes a phenomenon seen in coevolving populations—to maintain relative fitness, each population must constantly adapt to the other.
Muller's ratchet
describes the process by which the genomes of an asexual population accumulate deleterious mutations in an irreversible manner.
Fecundity
describes the reproductive capacity of an individual, such as the number and quality of eggs or sperm. As a measure of relative fitness, fecundity refers to the number of offspring produced by an organism.
The hypothesis of ecological character displacement proposes a possible mechanism to explain how divergence occurs. According to this hypothesis, if two species compete for a resource, such as a specific type of food, individuals in both species will face intense competition for the resource. A few individuals in one or both of the species may be able to exploit an alternative resource that cannot be used by most of the individuals in either species. Because these few use a different resource than the rest of their species, they will face less competition and have more success reproducing. Eventually, the two species will become less alike in the way they use the resource through _____ selection
directional
QTL and GWA mapping identifies regions of the genome associated with phenotypic variation
first step toward elucidating genes responsible for phenotypic variation
long term studies reveal _____ in the direction and strength of natural selection
fluctuation
when components of variation are additive
genetic and environmental variance sum to total phenotypic variance
For QTL analysis, scientists correlate phenotypic variation with genetic variation by using
genetic markers
alleles can spread rapidly in populations via
hybridization
detecting linkage disequilibrium can be very
informative
Polygyny
is a mating system where males mate (or attempt to mate) with multiple females.
Artificial selection
is similar to natural selection, except that it results from human activity. When breeders nonrandomly choose individuals with economically favorable traits to use as breeding stock, they impose strong artificial selection on those traits.
Genetic load
is the burden imposed by the accumulation of deleterious mutations
Researchers found that the size of the gall is dependent on the genotype of the _____ and is an example of an _____ phenotype. This phenotype is both variable and _____. In this example, _____ is the main force acting on gall size.
larva, extended, heritable, stabilizing selection
The close proximity of genes increases the probability of
linkage disequilibrium
Alleles for loci on different chromosomes are generally in
linkage equilibrium
Genome-wide association (GWA)
mapping involves scanning through the genomes of many different individuals, some with, and others without, a focal trait of interest, to search for markers associated with expression of the trait.
narrow sense heritability
more accurately reflects specific, additive components of genetic variation to offspring
Atlantic and Gulf Coast populations evolved white fur independently, and the specific _____ responsible are ______
mutations, different
Loci that are statistically correlated with the trait of interest usually indicate that _____ contribute to phenotypic variation in the trait.
nearby genes
an understanding of evolutionary biology can lead to _____ practices
novel management
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.
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.
genetics is the study of evolutionary mechanisms of continuous variation in phenotypic traits
quantitative
The closer two genes are to one another on a chromosome, the less likely it is that _____ will occur between the genes
recombination
the probability of recombination between alleles for loci on the same chromosome is dependent on the distance between them
reduced probability for loci that are closer together
Sexual selection
refers to differential reproductive success resulting from the competition for fertilization, which can occur through competition among individuals of the same sex (intrasexual selection) or through attraction to the opposite sex (intersexual selection).
Ecological character displacement
refers to evolution driven by competition between species for a shared resource (for example, food). Traits evolve in opposing directions, minimizing overlap between the species.
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.
Twofold cost of sex
refers to the disadvantages of being a sexual rather than an asexual organism. Asexual lineages multiply faster than sexual lineages because all progeny are capable of producing offspring. In sexual lineages, half of the offspring are males who cannot themselves produce offspring. This limitation effectively halves the rate of replication of sexual species.
Reaction norm
refers to the pattern of phenotypic expression of a single genotype across a range of environments. In a sense, they depict how development maps the genotype into the phenotype as a function of the environment.
direct benefit
a benefit that affects a particular female directly, such as food, nest sites, or protection.
Some snowshoe hare populations have brown fur instead of white fur in winter. What evolutionary events do scientists believe led to winter‑brown fur in these populations? -Introgression with black‑eared jackrabbits introduced an Agouti allele for winter‑brown fur into some snowshoe hare populations. -Winter-brown snowshoe hares are a unique species that is a hybrid between winter‑white snowshoe hares and black‑eared jackrabbits. -After the last Ice Age, climate change allowed for snow‑free winters, and natural selection favored the Agouti allele for winter‑brown fur. -Genetic drift resulted in the fixation of the winter‑brown Agouti allele in a small population of snowshoe hares isolated by Ice Age glaciers.
-Introgression with black‑eared jackrabbits introduced an Agouti allele for winter‑brown fur into some snowshoe hare populations. -After the last Ice Age, climate change allowed for snow‑free winters, and natural selection favored the Agouti allele for winter‑brown fur.
What uses have scientists found for linkage disequilibrium?
-Linkage disequilibrium allows scientists to offer inexpensive tests for inherited risks for certain diseases. -Linkage disequilibrium can show scientists a gene's location if known genetic markers correlate with a phenotype. -The level of linkage disequilibrium helps scientists determine how long an allele has been in existence.
Select each statement that provides evidence that artificial selection has occurred. -Livestock are less aggressive and more tolerant of penning than their wild counterparts. -Maize harvested 4,400 years ago shows the same genetic variation as the ancient teosinte. -Harvested wheat plants have traits that make them easier to gather than wild wheat plants. -The gray wolf understands human communication no better than its red wolf subspecies. -Kale, Brussels sprouts, cauliflower, and broccoli are the same species, Brassica oleracea.
-Livestock are less aggressive and more tolerant of penning than their wild counterparts. -Harvested wheat plants have traits that make them easier to gather than wild wheat plants. -Kale, Brussels sprouts, cauliflower, and broccoli are the same species, Brassica oleracea.
What characteristics of stickleback fish make them ideal for studying natural selection in the wild? -Stickleback populations are in environments with or without predators. -Variation in the number of armor plates is caused by codominant genes. -Heritable variation in armor directly affects the fitness of sticklebacks. -Some stickleback populations are isolated in closed environments. -The fossil record extends to the evolution of the first stickleback fish.
-Stickleback populations are in environments with or without predators. -Heritable variation in armor directly affects the fitness of sticklebacks. -Some stickleback populations are isolated in closed environments.
broad sense heritability includes:
-additive effects -dominance effects -epistatic effects -influences of the parent phenotype in the environment of offspring that can cause siblings to resemble each other
Advantages of Sex
-combining beneficial mutations -generation of novel genotypes -faster evolution -clearance of deleterious mutations
Selection on quantitative traits can take several different forms
-directional -stabilizing -disruptive
populations that independently experience parallel environmental changes represent replicated natural experiments
-ideal for evolutionary studies -examples include multiple islands or lakes invaded by new species or novel alleles
The speed of evolution depends on amount of genetic variation and strength of selection (think breeder's equation)
-many populations that humans seek to control are huge with lots of genetic variation -pesticides/herbicides/antibiotics exert extremely strong selection -leads to rapid resistance in pest populations
the evolutionary response (R) depends on
-strength of selection (selection differential, S) -heritability of the trait (h^2)
descriptions of narrow sense heritability
-the proportion of phenotypic variance due to only the additive effects of alleles -describes how closely offspring resemble their parents -can be estimated to predict evolution through natural selection
descriptions of broad sense heritability
-the proportion of phenotypic variance due to total genetic variance -includes genetic variance due to epistasis, dominance, and additive alleles -is a useful method to measure genetic versus environmental effects on phenotypic variation
In which of these scenarios would quantitative trait locus (QTL) analysis be useful?
-to identify which genes increase the risk of cardiovascular disease in humans -to locate all the genes that influence the mating dances of birds of paradise -to determine how many chromosomes influence seed weight in the plant Arabidopsis thaliana
Beak size is strongly heritable and influences fitness
-varies in intensity, depending on environment -natural selection can cause rapid change that can be documented in natural populations by scientists
Select the statement that describes how a biased operational sex ratio (OSR) can generate strong sexual selection.
An OSR can create intense competition between members of the more abundant sex.
Suppose scientists studied a species of plant that grows in shady environments. They measured the size of leaves in two plant populations and found that the size distribution was similar. In addition, they found that plants with larger leaves tended to produce more seeds and that their offspring tended to have large leaves. The scientists also measured the selection differential, S, of leaf size in each population. In population A, S equalled 1 cm2.1 cm2. In population B, S equalled 2 cm2.
After a given number of generations, the leaves in population B will be larger than those in A. Because S is larger in population B, leaf size will evolve more rapidly in population B than in A.
Fisher-Good Genes Process (Combination)
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 often are costly indicators of male quality. Thus, a Fisher process of linkage disequilibrium between ornament and preference applies to a "good genes" indicator trait
additive allele
Describes an allele that yields twice the phenotypic effect when two copies are present at a given locus than occurs when only one copy is present
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. This hypothesis assumes that among-male variation in the expression of ornaments reliably signals individual differences 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 physiological condition
How does anisogamy influence mating strategies?
Males fight for access to females to secure mating opportunities.
Why do calculations for narrow sense heritability not include dominance or epistasis?
The effects of dominance and epistasis depend on the presence of other inherited alleles.
Natural selection can lead to different variation ___________________, just as it can in a single habitat over time (ex Daphne Major)
across habitats or environments
lek
an assemblage of rival males who cluster together to perform courtship displays in close proximity.
hermaphrodite
an individual that produces both female and male gametes.
differences in phenotypic plasticity may be heritable,
and adaptive phenotypic plasticity can therefore evolve
Additive effects of alleles or nonadditive interactions among alleles, also known as _____ may influence trait expression.
epistasis
Linkage equilibrium
exists for any two loci if the occurrence of an allele at one of the loci is independent of the presence or absence of an allele at the other locus.
Linkage disequilibrium
exists for any two loci if the occurrence of an allele at one of the loci is n associated with the presence or absence of an allele at the other locus
polygenic
expression is influenced by many genetic loci
Disruptive selection
favors individuals at the tails of the distribution of phenotypes present in a population (for example, by acting against individuals with intermediate trait values).
Stabilizing selection
favors individuals in the middle of the distribution of phenotypes present in a population (for example, by acting against individuals at either extreme).
Directional selection
favors individuals on one end of the distribution of phenotypes present in a population.
Quantitative trait locus (QTL) analysis links the _____ of a quantitative trait to ____, called loci
phenotypic variation, genetic regions of interest
of alleles in response to the environment may affect the degree of their expression
plasticity
Continuous, or quantitative, traits are frequently _____ traits that depend on alleles at multiple loci
polygenic
