Patterns of Character Evolution p 78 83 Evolution Exam 3 3 3 The evolution of Flower Color in an Experimental Snapdragon Population Establish if natural selection of bumblebees could influence the evolution of a floral trait controlled by alleles of a single gene o Postulate 1 There is a variation among Individuals o Postulate 2 Some of the variation is Heritable o Postulate 3 Do Individuals vary in their Success at Surviving or Reproducing o Postulate 4 Is reproduction nonrandom o As a result of all of these postulates the result was the population evolved As long as the two first postulates hold true 3 4 The Evolution of Beak Shape in Galapagos Finches The deepest split on the tree separates two lineages of warbler finches that still recognize each other as potential mates and are thus classified as belonging to a single species Theory of Evolution by Natural Selection Daphne Major s size and location make it a perfect natural laboratory Population is small and there is little migration o Postulate 1 Is the Finch Population Variable Variation in beak depth o Postulate 2 Is Some of the Variation among Individuals Heritable Individual finches could vary in beak depth because the environments they have experienced are different or because their genotypes are different or both Heritability of a trait is defined as the proportion of the variation observed in a population that is due to variation in genes Therefore heritability varies between 0 and 1 In finches the beak depths of parents and offspring are similar This observation suggests that some alleles tend to produce shallow beaks while other alleles tend to produce deeper beaks A substantial fraction of the variation in beak size is due to variation in genotype p 267 290 Inbreeding that is less extreme than selfing produces the same effect as selfing it increases the proportion of homozygotes but at a slower rate Coefficient of inbreeding F the probability that the two alleles in an individual are identical by descent o Inbreeding Depression exposure of deleterious alleles to selection May lead to reduced fitness if it generates offspring homozygous for deleterious alleles Inbreeding effects are often easiest to detect when plants undergo some sot of environmental stress Inbreeding effects are much more likely to show up later in the life cycle o Nonrandom mating does not by itself alter allele frequencies It is not a mechanism of evolution Nonrandom mating does however alter the frequencies of genotypes It can thereby change the distribution of phenotypes in a population and alter the pattern of natural selection and the evolution of the population Inbreeding increases the frequency of homozygotes and decreases the frequency of heterozygotes 7 5 Conservation Genetics of the Illinois Greater Prairie Chicken o Destruction of prairie directly reduced the size of the bird s population and also fragmented the population that remained Small populations with little or no gene flow are precisely the setting in which genetic drift is most powerful Genetic drift results in random fixation and declining heterozygosity A reduction in fitness due to genetic drift is reminiscent of inbreeding depression Inbreeding depression in remnant populations of greater prairie chickens was caused by a loss of allelic diversity under genetic drift Migration in the form of birds transported by biologists appears to be restoring genetic diversity to remnant populations and alleviating inbreeding depression Chapter 8 Evolution at Multiple Loci Linkage and Sex o Evolution at Two Loci Linkage Equilibrium and Linkage Disequilibrium The multilocus genotype of a chromosome or gamete is sometimes referred to as its haplotype A pair of populations can have identical allele frequencies but different chromosome frequencies o Two Loci in a population are in linkage equilibrium when the genotype of a chromosome at one locus is independent of its genotype at the other locus knowing the genotype of the chromosome at one locus is of no use in predicting the genotype at the other Under HW chromosome frequencies remain unchanged from one generation to the next if the loci are in linkage equilibrium o Two loci are in linkage disequilibrium when there is a nonrandom association between a chromosomes genotype at one locus and its genotype at the other locus Each generation the chromosome frequencies move closer to linkage equilibrium if the loci are in linkage disequilibrium Three mechanisms create linkage disequilibrium in a random mating population Selection on multilocus genotypes Genetic drift Population admixture Genetic recombination eliminates linkage disequilibrium p 384 392 Tradeoffs and Constraints o Female Flower Size in a Begonia A tradeoff Inflorescences with more flowers may be favored by selection for two reasons Bees may be more attracted to inflorescences with more flowers More female flowers mean greater potential seed production o Host Shifts in an Herbivorous Beetle Constrained by Lack of Genetic Variation Genetic variation is the raw material for evolution by natural selection Chapter 11 Sexual Selection 11 1 Sexual Dimorphism and Sex Sexual Dimorphism the difference between the males and females of a species Differential reproductive success due to variation among individuals in success at getting mates is called sexual selection o Asymmetries in Sexual Reproduction Parental investment energy and time expending both in constructing an offspring and in caring for it Parental investment is measured in fitness It increases the reproductive success of the offspring receiving it It decreases the reproductive success that the investing parent may achieve in the future by way of additional offspring o In more than 90 of mammal species females provide substantial parental care and males provide little or none The key to explaining sexual dimorphism is in recognizing that sexual reproduction imposes different selection pressures on females versus males o When one parent invests more than the other in each offspring the reproductive success of the heavily investing parent is often limited by time and resources In contrast the reproductive success of the lightly investing parent is limited by number of mates o Asymmetric Limits on Reproductive Success in Newts and Pipefish NEWTS Sexual selection is a more potent force in the evolution of males than in the evolution of females Heritable traits that are associated in males with failure to mate will tend to