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NAME: KEY EVOLUTIONARY BIOLOGY BIOS 30305 EXAM #2 FALL 2016 There are 3 parts to this exam. Take your time and be sure to put your name on the top of each page. Part I. True (T) or False (F) (2 points each)(30 pts. total) 1) Quantitative Trait Loci (QTL) studies based on crosses between divergent individuals are used to estimate the number of genes (or genomic regions) that influence phenotypic variation T F Mate provisioning is an example of an indirect benefit driving the evolution of female preference. T F Sympatric speciation relies on geographic isolation of potentially interbreeding populations. T F Introgression is the exchange of alleles between species following hybridization and backcrossing. T F Antagonistic-Pleiotropy among fitness traits can maintain genetic variance for fitness in natural populations T F There is a higher opportunity for sexual selection in species with strictly monogamous mating systems than in species with polygynous mating systems. T F Rapid divergence of secondary sexual characteristics in closely related species provides evidence for reinforcement. T F Male-male competition leads to a reduced variance in male reproductive success T F Similar ecological conditions can lead to parallel evolution of similar phenotypes. T F 10) In small captive populations, doubling the effective size of the population maintains twice the amount of additive genetic variation. T F 11) An estimate of the heritability of human I.Q. can tell us whether the difference in I.Q. among different populations is due to environmental factors. T F 12) Using Prices’ Rule, the selection differential (S) on relative fitness is equal to the phenotypic variance (VP) in relative fitness. T F 2) 3) 4) 5) 6) 7) 8) 9) 1 NAME: KEY 13) An analysis of Bateman’s Gradient in sex-role reversed pipefish indicates that there is a greater opportunity for sexual selection in females in this species. T F 14) Ring species demonstrate the development of instantaneous reproductive isolation among adjacent populations. T F 15) On average, paternal half-siblings should resemble each other more than grandparents and grandchildren. T F Part II. Multiple Choice (3 points each)(45 pts total). 16) When populations are in a rapidly changing environment they can, A. Physically move to a more beneficial environment B. Adapt to the changing environment and maintain high population fitness. C. Adapt at a rate that is slower that the critical rate necessary to track the moving optimum and eventually go extinct. D. All of the above. 17) Stabilizing selection occurs when… A. The individuals with extremely small and large trait values have lower fitness than those with intermediate trait values. B. The individuals with intermediate trait values have lower fitness than those with extremely small and large trait values. C. The individuals with small trait values have lower fitness than those with larger trait values. D. All individuals have equal fitness. 18) One form of the Good-Genes model for the evolution of female choice is the handicap principle. Which of the following statements is NOT true under the handicap principle? A. Handicaps are examples of honest signals since there is a true cost to elaborate male traits. B. Females who mate with males carrying an exaggerated trait will have female offspring with decreased fitness. C. The bigger the handicap, the higher the genetic quality of the male carrying the trait. D. Female preference for exaggerated male traits can lead to a genetic correlation between preference and trait. 2 NAME: 19) KEY Which of the following statements about character displacement is/are TRUE? A. Character displacement can promote rapid divergence among closely related species. B. Character displacement is the divergence of male and female traits involved in sexual selection. C. Character displacement can constrain divergence into occupied niches. D. A and B. E. A and C. 20) What is the best definition of sexual selection? A. B. C. D. 21) Anisogamy refers to, A. B. C. D. 22) Mating occurs, but no gametes are transferred. The backcross or F2 has reduced viability. Mating occurs, gametes are transferred, but fertilization does not take place. Populations are infected with different strains of the bacteria Wolbachia causing reciprocal male sterility. The observation that two loci are in linkage disequilibrium means… A. B. C. D. 24) A positive relationship between size and fecundity. A non-random mating process in which one sex competes for the other. An asymmetry in the size of gametes, with one small type and one large type. Asymmetrical sperm with a large amount of shape variation. Which one of the following is NOT a prezygotic reproductive isolating mechanism? A. B. C. D. 23) Selection related to any aspect of offspring production. Selection that arises as a consequence of competition for access to mates. Selection on the form and structure of gametes. Selection that results in any type of difference between the sexes. That they exhibit a non-random association of alleles. That they are close to one another on a chromosome. That the loci are functionally related. That selection is operating on the loci. Which of the following statements best describes the reason for barriers to gene flow when there is postzygotic isolation? A. B. C. D. Individuals from different populations meet but do not mate Copulation occurs, but gametes are not transferred Gametes are transferred, but eggs are not fertilized Gametes are transferred, eggs are fertilized, but the zygote dies 3 NAME: 25) Which of the following statements about heritability is TRUE? A. B. C. D. 26) KEY Heritability is the additive genetic variance divided by the total genetic variance. Traits that have a genetic basis always have high heritability. Heritability is equal to the selection differential divided by the response to selection. A higher heritability permits a greater evolutionary response to selection. Which of the following statements is NOT true? A. The selection differential is the covariance between phenotype and relative fitness. B. The selection differential is the difference between the mean of selected parents and the mean of the base population prior to selection. C. The selection differential is the difference between the mean of the offspring of selected parents and the mean of the offspring of all parents. D. The selection differential is equal to the response to selection divided by the heritability. 28) Epistatic interactions are an important component of which of the following? A. The build up of postzygotic reproductive isolating mechanisms. B. The phenotypic covariance between half-sibs. C. The almost universal observation of inbreeding depression in natural populations following the mating of related individuals. D. A and C. 29) Which of the following statements best describes the three phases of Wright’s ShiftingBalance model of movement between peaks in an adaptive landscape? A. Migration followed by random genetic drift and selection towards a new fitness optima. B. Selection towards a new fitness optima followed by random genetic drift and migration. C. Random genetic drift followed by selection towards a new fitness optima and migration. D. The appearance of a rare beneficial mutation followed by selection towards a new fitness optima and migration. 30) The Biological Species Concept (BSC) defines species as: A. Actually or potentially interbreeding populations that are reproductively isolated from other such populations. B. Populations that form the smallest diagnosable cluster, or group, distinct from other such clusters. C. Both A and B D. None of the above 4 NAME: KEY Part III. Short Answer (25 pts. total) Be concise and to the point, short focused answers are better than long rambling ones. 31) It is generally thought that it takes more than a single gene for the evolution of reproductive isolation leading to speciation. What is the problem with a one locus model of speciation? How does the Bateson-Muller-Dobzansky 2-locus model of speciation get around this difficulty? (4 points) The single-locus model requires that populations cross a fitness valley created by heterozygote disadvantage. Since selection will always move a populations upwards on a fitness landscape this model is unlikely since the initial mutation from A to a (or a to A) in a single population will be deleterious and selection will prevent it from rising to high frequency. In very small populations experiencing strong drift we know that gene frequencies can move in the opposite direction from that favored by selection, so drift is one possible way to “rescue” this single-locus model. The B-M-D two-locus model of speciation circumvents the problem of the one-locus model by the accumulation of independent mutations that are neutral or beneficial in the genetic background they arise in, but have negative epistatic interactions when put in the same genetic background. These negative epistatic interactions cause a decrease in hybrid fitness that contributes to reproductive isolation. Bonus (1 pt): How does Haldane’s Rule support the BMD model? The dominance theory for Hadane’s rule relies on 1) multiple genes and 2) negative epistatic interactions. Both are features of the 2-locus B-M-D Model. 5 NAME: KEY 32) Examine the plots above from the work of Coyne and Orr (1997). It appears that the degree of prezygotic isolation is lower for allopatric pairs of species that have been geographically isolated than for pairs that exist in sympatry. (4 points) What is the likely explanation for this observation? The work of Coyne and Orr (1997) comparing the patterns of pre- and postzygotic isolation for species pairs of Drosophila best illustrates the action of REINFORCING MECHANISMS. Sympatric species pairs develop prezygotic isolation at a faster rate than do allopatric species pairs. The likely explanation is that REINFORCEMENT has played a role in establishing reproductive isolation in sympatric, but not allopatric species pairs. Allopatric populations cannot interbreed to create hybrids so a deficit in hybrid fitness cannot cause a fitness loss to individuals in the two species. Sympatric species can interbreed so a deficit in hybrid fitness leads to strong selection against hybridization. If this reinforcing selection is not strong enough to counteract the homogenizing effect of gene flow the species will reunite and will not be represented on this plot. The two key elements are 1) a defict in hybrid fitness, 2) reinforcement favoring prezygotic isolating mechanisms that prevent the loss of fitness due to this deficit. 33) Female preference for male traits can drive the evolution of exaggerated male traits. List and explain three (3) theories for the evolution of female preference. (9 points) There are a number of possible answers to this question. These include: 1) Direct Benefits (i.e., mate provisioning, nuptial gifts) 2) Indirect Benefits: Good-genes Model: the key element of this model is preference by females for males that are carrying high fitness genes 6 NAME: KEY Handicap Principle: this model is an example of “honest signaling” by males advertising high-fitness genes that overcome a fitness handicap. The main indirect fitness benefit for females is in daughters that inherit these high-fitness alleles. Fisherian Runaway Process: this model requires a genetic correlation between female preference and male trait. This process begins with a pattern of assortative mating that leads to linkage disequilibrium between preference and trait alleles. Sexy-son Hypothesis: one way to couch the runaway process that emphasizes that the indirect fitness benefit to females is sons with exaggerated traits and a mating advantage Antagonistic Coevolution: An alternative to the Good Genes Model is based on Sexual Conflict. Just like the good genes models the genetic correlations created by assortative mating can lead to a runaway process. 3) Sensory Bias: Pre-existing preferences that are “hard wired” due to the sensory machinery in females. Any three of these was acceptable. Full credit was not given if good Genes & Handicap principle, or Sexy-son and Fisherian run away were used together since they are not distinct from one another. For each, a reasonable explanation was required. Bonus (1 pt): Which of these theories best explains the origin of female preference? This question was evaluated based on what you had down for the first part. Sensory Bias most directly addresses the question of the origin of female preference since it does not require selection at all. Among the others, anytime there are direct benefits the selection pressure on females will be the highest since there is a direct effect on her individual fitness. Antagonistic coevolution also directly affects the female so this one would be next. All the other categories are an indirect benefit and are more applicable to the evolution of female preference and male trait after they are established in a population. Among these, a good genes model is the best choice. 34) The rapid diversification of species is a hallmark of an Adaptive Radiation. Paleontologist G. G. Simpson suggested that two main factors contribute to an Adaptive Radiation. List and explain these two factors, and provide an example from an actual adaptive radiation for each factor. (8 points) Two factors suggested by the paleontologist G. G. Simpson that play a role in adaptive radiations are: 1) ECOLOGICAL OPPORTUNITY - Can be the result of the invasion of unoccupied territory, or the extinction of a competitor opening up an available niche. The main feature is the availability of unoccupied niches. When there is open niche space for species to diversify into, mechanisms like character displacement can rapidly promote diversification. There are many examples of ecological opportunity that could be used. 7 NAME: KEY 2) KEY INNOVATION- The evolution of a novel trait can lead to an adaptive radiation by opening up new niches and exposing organisms to novel selection pressures promoting divergence. There are many examples of key innovations that could be used. 8 NAME: KEY Extra Work Space: Section 1 Section 2 Section 3 Total /30 /45 /25 /100 9 NAME: KEY Components of Phenotypic Variation: VP VG VE , where VP is the total phenotypic variance, VG is the total genetic variance and VE is the environmental variance. Components of Genetic Variation: VG VA VD VI , where VG is the total genetic variance, VA is the additive genetic variance, VD is the dominance genetic variance, and VI is the epistatic genetic variance. Slope of a regression line of two variables x and y: b Cov x, y Var x Heritability: h2 VA VA VP VG VE The Univariate Breeder’s Equation: R h 2 S , where R is the response to selection, h2 is the heritability, and S is the selection differential. Price’s rule: S = Cov(relative fitness, phenotype) S 1 N w w P P i i VA under drift-mutation equilibrium: VA 2 NVm , where Vm is the genetic variance due to the input by mutation 10