Quiz 2 Study Guide
Quiz 2 Study Guide Bios 207
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This 4 page Study Guide was uploaded by Cara Cahalan on Thursday April 7, 2016. The Study Guide belongs to Bios 207 at University of Nebraska Lincoln taught by in Spring 2016. Since its upload, it has received 8 views. For similar materials see Ecology and Evolution in Biology at University of Nebraska Lincoln.
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Date Created: 04/07/16
Quiz 2 Study Guide 1 1/25: Genetic Drift Class: Evolution easily visible in many systems if traits or gene frequencies are tracked through time Populations evolve through a variety of mechanisms: o HardyWeinberg equilibrium (random mating, no migration, genetic drift, mutation, natural selection) allele frequencies do not change o Drift (imperfect sampling causes some allele to be underrepresented relative to others) allele is lost o Natural selection (environmental factors are unfavorable for red alleles) red allele less common o Migration (individuals with new allele enters population) allele that enters becomes more common o Mutation (red allele becomes orange) new genetic variant appears in the population Genetic drift results from random sampling error: o Sampling error is higher with smaller samples (more chance for drift) Founder effect causes genetic drift Bottlenecks reduce genetic variation Natural selection more powerful in large populations o Drift weaker in large populations o Small advantages in fitness can lead to large changes over a long time Readings: Population genetics study distribution of alleles in a population and mechanisms that can cause allele frequency to change overtime HardyWeinberg equilibrium without outside forces, allele frequency in a population will not change no evolution o Assumptions of equilibrium: Population is infinitely large (drift) Alleles are equally likely to survive/reproduce (selection) No migration No mutation Null hypothesis no relationship between phenomena Fixed allele allele that remains in a population when all alternative alleles have disappeared no genetic variation Alleles lost due to drift more quickly in small populations Genetic bottleneck population drastically reduced (even if temporary) can have large effect o Cause loss of alleles in small population o Genetic variation remain low after population rebound Founder’s effect small number migrate away from population, genetic drift loss of allelic variation due to migration of small population, new population is considerably different Relative fitness describes success of genotype at producing new individuals (fitness) standardized by success of other genotypes in the population Average excess of fitness different between average fitness of individuals bearing the allele and average fitness of the population as a whole Allele is slightly higher average success for fitness can come to dominate a population Antagonistic pleiotropy beneficial mutation for one trait also causes detrimental effects on other traits 2/1: Sexual Selection Class: Anisogamy results in differential investment (sperm/egg) in reproduction Foundation of sexual selection o Females and males invest different amounts of resources and time into offspring (females more) o Operational sex ratio ratio of males to females capable of reproducing at a given time Quiz 2 Study Guide 2 Males don’t get pregnant and can therefore keep mating, creating a ‘surplus’ of males and a shortage of females o Males have to compete for access to females Intrasexual selection – malemale competition o Males compete/fight for access to females, resources, and territories o Females mate with whichever male wins Intersexual selection – female choice o Males advertise their ‘quality’ with ornaments, colors, songs, or dances, and females pick the best Why is male reproduction more compressed than females? o Malemale competition delays offspring o Malemale competition shortens lifespan Male vs. Female in sexual selection: o Male: low investment, not so choosy, male has that trait, trait is heritable o Female: high investment, choosy, preference for a trait that indicates “quality”, preference is heritable Female population is often consistent Female preferences sometimes don’t make sense, they may arise from preexisting sensory bias (orange disks) Is tail length a reliable indicator of male quality? No What are consequences of being chosen because of your long tail? Higher fitness and greater risk of starvation Benefits of female choice: o Direct benefits benefit the female directly (i.e. food, nest sites, protection) o Indirect benefits benefits that affect the genetic quality of female’s offspring Birds of Paradise (A2): o Female choice: Preference for heritable trait Heritable trait Trait quantitative Females are choosy Choice of extreme phenotype Phenotypic Plasticity (A1): o Reaction norm pattern of phenotypic expression of a single genotype across a range of environments o Can select for specific reaction norms Readings: Fecundity reproductive capacity of an individual, number of offspring produced by an organism Certainty of paternity probability male is father of offspring, may be much lower than female’s certainty o When offspring require extra care female provides Sexual selection differential reproductive success resulting from competition within a population Sexual dimorphism different form between males and females of a species (i.e. presence/absence of structures used in courtship display) Quiz 2 Study Guide 3 Opportunity for selection variance in fitness within a population o No variance no selection o Large variance greater opportunity for selection Leks male rivals cluster to perform courtship displays in close proximity Another indirect benefit is mating with high quality males (genetically) to improve offspring genetics “Honest signals” an animal has to pay to cost to display it (antlers) 2/3: Evolution of Sex Asexual reproducing organism can continuously divide into identical organisms, all organisms can reproduce Sexual reproducing organism only females can give birth, limiting reproductive population Two fold cost of sex makes 2 assumptions: o 50:50 sex ratio o Number of offspring constant through time Other factors can undermine twofold cost of sex: o Violation of first assumption females can lay lots of eggs (channel catfish egg mass) Cycle: repeat o Parasites grow abundant o Number of hosts decimated o Parasites then starve and decline o Host begins to recover Red Queen Effect running to stand still, evolve rapidly just to compete Why would sexual reproduction make the recovery of hosts more likely? o Genes influence susceptibility to infection o Recombination o Deleterious alleles can be selected against o All of the above The positive correlation between frequency of males and trematode parasite infection is evidence for what? o Red Queen hypothesis o That sex is unrelated to parasite resistance o That sex is beneficial to evolving resistance to parasites o More than one of these o No evidence at all Readings: Two fold cost of sex disadvantage of being sexual rather than asexual o Asexual multiply faster than sexual because all progeny are capable of producing offspring o Sexual males can’t reproduce ½ rate of replication Novelty new genetic variations from sexual reproduction Muller’s ratchet asexual genomes accumulate deleterious mutations irreversibly, can’t separate good/bad mutations in genome Genetic load burden imposed by accumulation of deleterious mutations 2/5: Evolution in the Wild Quiz 2 Study Guide 4 Class: Everything so far: o Selection differential (S) seen in shift in beak depths Directional selection o Natural selection drought caused environment to select for finches with larger beak depths Big seeded plants still available selecting for larger beak Finches with small seeds don’t have enough energy to reproduce or live o Heritability trait heritable to next generation (seen in green graph) Narrow sense o Correlation offspring to parent (additive variance) Slope of parent offspring regression heritability o Breeders equation: Response to selection, green graph Coat color variation affects fitness by influencing predation risk o Light mice survive better in light environment (near the coast) o Darker mice survive better in darker environment (inland) King snake mimicry o In overlap area mimicry by scarlet king snakes of coral snakes o Outside overlap area mimicry is less common because bright coloration attracts predators Readings: Natural selection may vary in intensity Pattern of selection can change over time Closely related population under the same selective pressure often evolve the same phenotype in parallel, but can occur through different mutations Gene flow movement of alleles between populations Aposematism antipredator strategy used by prey to signal danger (i.e. warning coloration of prey to deter predators) 2/8: Humans as Selective Agents Class: Selection differential on quantitative traits that selected for desired traits (i.e. corn and rice) Reading: Domestication as well as hunting/fishing both have evolutionary effects, but they are opposite o Domestication individual plants are breed because they have desirable traits o Hunting/fishing undesirable individuals can survive and pass on their traits to the next generation Elk example elk with the largest antlers are being killed, but they have the highest breeding success Understanding of evolutionary biology can lead to novel management practices, which slow evolution of resistance in pest populations, or minimize evolutionary consequences of harvesting Speed of evolution is a product of the amount of available genetic variation and strength of selection o Weed and pest populations have high variability, herbicides and pesticides impose strong selection rapid evolution of resistance
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