Darwin Genetics Population Genetics and The Modern Synthesis Modern Evolutionary Theory A. Peripatric Speciation

Population Genetics and The Modern Synthesis Darwin Genetics Population Genetics and The Modern Synthesis Modern Evolutionary Theory A. Peripatric Speciation B. Punctuated Equilibrium Niles Eldridge Stephen J. Gould

B. Punctuated Equilibrium – Eldridge and Gould 1. Consider a large, well-adapted population VARIATION TIME

B. Punctuated Equilibrium – Eldridge and Gould 1. Consider a large, well-adapted population Effects of Selection and Drift are small - little change over time VARIATION TIME

B. Punctuated Equilibrium – Eldridge and Gould 2. There are always small sub-populations "budding off" along the periphery of a species range... VARIATION TIME

X X X B. Punctuated Equilibrium – Eldridge and Gould 2. Most will go extinct, but some may survive... VARIATION X X X TIME

X X X B. Punctuated Equilibrium – Eldridge and Gould 2. These surviving populations will initially be small, and in a new environment...so the effects of Selection and Drift should be strong... VARIATION X X X TIME

X X X B. Punctuated Equilibrium – Eldridge and Gould 3. These populations will change rapidly in response... VARIATION X X X TIME

X X X B. Punctuated Equilibrium – Eldridge and Gould 3. These populations will change rapidly in response... and as they adapt (in response to selection), their populations should increase in size (because of increasing reproductive success, by definition). VARIATION X X X TIME

X X X B. Punctuated Equilibrium – Eldridge and Gould 3. As population increases in size, effects of drift decline... and as a population becomes better adapted, the effects of selection decline... so the rate of evolutionary change declines... VARIATION X X X TIME

X X X B. Punctuated Equilibrium – Eldridge and Gould 4. And we have large, well-adapted populations that will remain static as long as the environment is stable... VARIATION X X X TIME

X X X B. Punctuated Equilibrium – Eldridge and Gould 5. Since small, short-lived populations are less likely to leave a fossil, the fossil record can appear 'discontinuous' or 'imperfect' VARIATION X X X TIME

X X X B. Punctuated Equilibrium – Eldridge and Gould 5. Large pop's may leave a fossil.... VARIATION X X X TIME

X X X B. Punctuated Equilibrium – Eldridge and Gould 5. Small, short-lived populations probably won't... VARIATION X X X TIME

X X X B. Punctuated Equilibrium – Eldridge and Gould 6. So, the discontinuity in the fossil record is an expected result of our modern understanding of how evolution and speciation occur... VARIATION X X X TIME

X X X B. Punctuated Equilibrium – Eldridge and Gould 6. both in time (as we see), and in SPACE (as changing populations are probably NOT in same place as ancestral species). VARIATION X X X TIME

Population Genetics and The Modern Synthesis Darwin Genetics Population Genetics and The Modern Synthesis Modern Evolutionary Theory A. Peripatric Speciation B. Punctuated Equilibrium C. Genes and Development: “Evo-Devo” …explain changes like this? Can changes like this….

C. Genes and Development: "Evo-Devo" …explain changes like this? Can changes like this…. Differences correlate with what they make (different proteins make them different colors) Differences don’t correlate with what they make; they are pretty much the same stuff, just in a different shape.

C. Genes and Development: "Evo-Devo"

C. Evo-Devo – the influence of regulatory genes

Without Fish With Fish Antennules detect chemicals secreted by predatory fish Stimulate release of dopamine in the brain Brain releases juvenile hormone (growth hormone in inverts) Growth of particular body parts continues, creating a sharp “helmet” and longer “spine” that reduce predation. Selection for an inducible developmental pathway

Modern Evolutionary Theory A. Peripatric Speciation B. Punctuated Equilibrium C. Genes and Development: “Evo-Devo” D. Model Sources of Variation Agents of Change Mutation Natural Selection Recombination Drift - crossing over Mutation - independent assortment Migration Non-random Mating VARIATION D E V L O P M N T

Evolution Selection

A. ‘Artificial Selection’ and Domesticated Animals and Plants

A. ‘Artificial Selection’ and Domesticated Animals and Plants

A. ‘Artificial Selection’ and Domesticated Animals and Plants

A. ‘Artificial Selection’ and Domesticated Animals and Plants

A. ‘Artificial Selection’ and Domesticated Animals and Plants

A. ‘Artificial Selection’ and Domesticated Animals and Plants Selection can create phenotypes beyond the initial range of expression.. There are no adult wolves as small as chihuahuas.

Selection for change in energy allocation - from vegetative tissue to reproductive tissue

Matsuoka, et al. 2002. A single domestication for maize shown by multilocus microsatellite genotyping. PNAS 99: 6080-4.

Selection in wild mustard

II. Selection B. Natural Selection - Types of Selection

II. Natural Selection B. Natural Selection - Types of Selection Stabilizing selection for size at birth in humans

II. Natural Selection B. Natural Selection - Types of Selection Directional selection for beak size

Kettlewell, 1956

Speciation - Allopatric: The result of geographic isolation and subsequent divergence; often because of b-directional selection for different traits in different environments (corollary) ENV 1 ENV 2 Directional Directional Separate Populations

II. Natural Selection B. Natural Selection - Types of Selection Disruptive selection for beak width in African finches feeding on two species of sedges with soft and hard seeds. Same Population

Spadefoot toad mouthparts

Can result in sympatric speciation – speciation within a reproducing population, in which different subpopulations become adapted to different niches in the same environment and produce poorly adapted hybrids when they breed with other subpopulations.

Sympatric Speciation through polyploidy (mutation, not selection) Normal diploid species, mutant diploid gamete Normal diploid species, haploid gamete

II. Natural Selection B. Modes of Selection Natural Selection Sexual Selection: fitness of a genotype/trait depends on organism’s sex

II. Natural Selection B. Modes of Selection Natural Selection Sexual Selection: fitness of a genotype/trait depends on sex Kin Selection: fitness depends on relatedness within group

II. Natural Selection B. Modes of Selection Natural Selection Sexual Selection: fitness of a genotype/trait depends on sex Kin Selection: fitness depends on relatedness within group Frequency-dependent Selection: fitness depends on genotype frequency Papilio memnon females have many possible phenotypes that mimic toxic species. Abundant morphs are selected against; because bird predators learn they are tasty and prey on them. Negative frequency dependence. females

II. Natural Selection B. Modes of Selection Natural Selection Sexual Selection: fitness of a genotype/trait depends on sex Kin Selection: fitness depends on relatedness within group Frequency-dependent Selection: fitness depends on genotype frequency Female guppies prefer to mate with the rarest male phenotype; selects for polymorphism over time – Negative Frequency dependent selection

II. Natural Selection B. Modes of Selection Natural Selection Sexual Selection: fitness of a genotype/trait depends on sex Kin Selection: fitness depends on relatedness within group Frequency-dependent Selection: fitness depends on genotype frequency Heliconius erato is a toxic species in Central America. Whichever morph becomes more abundant (even by chance) becomes EVEN MORE abundant because birds learn to avoid it more readily. Positive frequency dependence.

II. Natural Selection Artificial Selection Modes of Selection C. Testing for Selection/Adaptation 1. Phenotypic Plasticity Why do populations differ? Genetic adaptation (selection) Evolutionary diverge due to other agents of change (drift) Phenotypic plasticity – the direct effect of environment on phenotype

Daphnia grow spines and head-spines when developing in the presence of fish (predators) Are these changes ‘adaptations’, or is one genome ‘acclimating’ to different environments? And is this ‘acclimation’ itself an adaptation? Gastrimargus grasshoppers developing in different seasons (with predictable sustrate colors) develop into different colored nymphs and adults

II. Natural Selection C. Testing for Selection/Adaptation Phenotypic Plasticity Genetics, environment, or genetic adaptation to environment?

II. Natural Selection C. Testing for Selection/Adaptation Phenotypic Plasticity Genetics, environment, or genetic adaptation to environment? So, suppose we observe variation in plant size among genetically different plants growing in a field: This variation in phenotype might be due to a combination of genetic and environmental differences between them. V(phen) = V(env) + V(gen)

II. Natural Selection C. Testing for Selection/Adaptation Phenotypic Plasticity Genetics, environment, or genetic adaptation to environment? IF these plants were all grown under the same environmental conditions (‘common garden’ experiment), then there is no variation in the environment and the variation we observe can be attributed to genetic differences. V(phen) = 0 + V(gen) (whether these genetic differences are ADAPTIVE is another question…)

II. Natural Selection C. Testing for Selection/Adaptation Phenotypic Plasticity Genetics, environment, or genetic adaptation to environment? IF these plants were all grown under the same environmental conditions (‘common garden’ experiment), then there is no variation in the environment and the variation we observe can be attributed to genetic differences. V(phen) = 0 + V(gen) (But this is only true for this environment!)

II. Natural Selection C. Testing for Selection/Adaptation Phenotypic Plasticity Genetics, environment, or genetic adaptation to environment? In a different environment, phenotypic and genetic variation may be expressed differently.

II. Natural Selection C. Testing for Selection/Adaptation Phenotypic Plasticity Genetics, environment, or genetic adaptation to environment? So, in a large population experiencing a range of environments: V(phen) = V(env) + V(gen) + V(g*e) V(g*e) is a genotype by environment interaction; reflecting the fact that genotypes may respond in different ways to changes in the environment.

II. Natural Selection C. Testing for Selection/Adaptation Phenotypic Plasticity Genetics, environment, or genetic adaptation to environment? Suppose we had populations of each genotype, and these were the mean heights of these populations. Genotype C F Height Stanford Mather Environment

II. Natural Selection C. Testing for Selection/Adaptation Phenotypic Plasticity Genetics, environment, or genetic adaptation to environment? Suppose we had populations of each genotype, and these were the mean heights of these populations. Genotype C F Height XS V(env) XM Stanford Mather Environment

II. Natural Selection C. Testing for Selection/Adaptation Phenotypic Plasticity Genetics, environment, or genetic adaptation to environment? Suppose we had populations of each genotype, and these were the mean heights of these populations. Genotype C F Height XC V(gen) XF Stanford Mather Environment

II. Natural Selection C. Testing for Selection/Adaptation Phenotypic Plasticity Genetics, environment, or genetic adaptation to environment? Suppose we had populations of each genotype, and these were the mean heights of these populations. Genotype C F Height XCS XCM = XFS XFM The effect of environment IS THE SAME for the two genotypes: (g*e) = 0. Stanford Mather Environment

II. Natural Selection C. Testing for Selection/Adaptation Phenotypic Plasticity Genetics, environment, or genetic adaptation to environment? So, in this comparison: V(phen) = V(env) + V(gen) + V(g*e) Sig. Sig. ns

II. Natural Selection C. Testing for Selection/Adaptation Phenotypic Plasticity Genetics, environment, or genetic adaptation to environment? Suppose we compare B and E. Genotype B E Height Stanford Mather Environment

II. Natural Selection C. Testing for Selection/Adaptation Phenotypic Plasticity Genetics, environment, or genetic adaptation to environment? Environmental effects are significant Genotype B E Height XS V(env) XM Stanford Mather Environment

II. Natural Selection C. Testing for Selection/Adaptation Phenotypic Plasticity Genetics, environment, or genetic adaptation to environment? Genetic effects are insignificant; means don’t differ. Genotype B E Height XC XE V(gen) = 0 Stanford Mather Environment

II. Natural Selection C. Testing for Selection/Adaptation Phenotypic Plasticity Genetics, environment, or genetic adaptation to environment? There is a significant ‘G x E’ interaction. Genotype B E Height XCS XCM >> XFS XFM The effect of environment IS NOT THE SAME for the two genotypes!! Stanford Mather Environment

II. Natural Selection C. Testing for Selection/Adaptation Phenotypic Plasticity Genetics, environment, or genetic adaptation to environment? In a different environment, phenotypic and genetic variation may be expressed differently. So, in this comparison: V(phen) = V(env) + V(gen) + V(g*e) Sig. ns Sig.

We should expect adaptations to specific environmental conditions to be reflected by such “genotype by environment” interactions in characters that affect reproductive success.

II. Natural Selection C. Testing for Selection/Adaptation Phenotypic Plasticity Genetics, environment, or genetic adaptation to environment? Selection for Acclimation Ability

II. Natural Selection C. Testing for Selection/Adaptation Phenotypic Plasticity Genetics, environment, or genetic adaptation to environment? Selection for Acclimation Ability Raised at 20oC Raised at 45oC

II. Natural Selection C. Testing for Selection/Adaptation Phenotypic Plasticity Genetics, environment, or genetic adaptation to environment? Selection for Acclimation Ability How could we test whether this is an environmental effect or a genetically adaptive pattern of acclimation?

II. Natural Selection C. Testing for Selection/Adaptation Phenotypic Plasticity Genetics, environment, or genetic adaptation to environment? Selection for Acclimation Ability How could we test whether this is an environmental effect or a genetically adaptive pattern of acclimation? Do other populations from aseasonal areas respond the same way, phenotypically.

II. Natural Selection C. Testing for Selection/Adaptation Phenotypic Plasticity Genetics, environment, or genetic adaptation to environment? Selection for Acclimation Ability Is the development of spines and head shields strictly environmentally induced, or is it a developmental adaptation? Introduce Daphnia that have never experienced fish… do they grow head shields?

II. Natural Selection C. Testing for Selection/Adaptation Phenotypic Plasticity Genetics, environment, or genetic adaptation to environment? Selection for Acclimation Ability Is the development of spines and head shields strictly environmentally induced, or is it a developmental adaptation? Introduce Daphnia that have never experienced fish… do they grow head shields? HOW do these acclimation adaptations evolve? Are there NEW structural genes that evolve?

Sources of Variation Agents of Change Mutation Natural Selection No. The difference is how they are modulated/regulated. Always on, always off, or developmentally dependent on environmental conditions. D. Model Sources of Variation Agents of Change Mutation Natural Selection Recombination Drift - crossing over Mutation - independent assortment Migration Non-random Mating VARIATION D E V L O P M N T