NaturalSelectionProblems_withanswers - Figure 1 2 r = 0.98 p < 0.001 midoffspring beak depth midoffspring beak depth Natural Selection Practice Question

NaturalSelectionProblems_withanswers - Figure 1 2 r = 0.98...

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Unformatted text preview: Figure 1 2 r = 0.98 p < 0.001 midoffspring beak depth midoffspring beak depth Natural Selection: Practice Question 1 Figure 2 2 r = -­‐0.18 p > 0.5 Q1. Variation in Song Sparrow Beaks Smith and Dhondt (1980) raised song sparrows in the nests of unrelated, foster parents to test whether beak depth was heritable, environmentally-­‐determined, or both. Eggs from 24 nests were transferred to foster nests. Beak size of all parents, including each offspring’s genetic (biological) parents and each offspring’s foster parents, was measured. When the young became adults, their beak size was also measured. a) Does figure 1 support or refute the hypothesis that variation in beak depth is heritable? Explain your answer. (max 2 sentences) b) Do figures 1 and 2 support or refute a hypothesis that environment has a large, significant affect on beak depth? Explain your answer (max 2 sentences) c) Why did the authors choose to raise birds in the presence of foster parents? (max 3 sentences) Natural Selection: Practice Problem 1 Q1. Variation in Song Sparrow Beaks Smith and Dhondt (1980) raised song sparrows in the nests of unrelated, foster parents to test whether beak depth was heritable, environmentally-­‐determined, or both. Eggs from 24 nests were transferred to foster nests. Beak size of all parents, including each offspring’s genetic (biological) parents and each offspring’s foster parents, was measured. When the young became adults, their beak size was also measured. a) Does figure 1 support or refute the hypothesis that variation in beak depth is heritable? Explain your answer. (max 2 sentences) Figure 1 supports the hypothesis that beak depth is heritable as there is a strong, significant, positive correlation between the depth of parents’ beaks and the depth of their offsprings’ beaks. b) Do figures 1 and 2 support or refute a hypothesis that environment has a large, significant affect on beak depth? Explain your answer (max 2 sentences) Taken together, figures 1 and 2 refute the hypothesis that environment has a large impact on beak depth, as we would expect to see an equal (or stronger) correlation between foster parent beaks and offspring beaks than biological parent beaks and offspring beaks if environment played a large, significant role. c) Why did the authors choose to raise birds in the presence of foster parents? (max 3 sentences) The correlation between biological parent beaks and offspring beaks could be driven by the birds having lived in the same environments and not genetics. The inclusion of data from foster parents provides strong evidence that the environment is playing less of a role than genetics. Natural%Selec3on:%Prac3ce%Ques3on%2% S.%Gulf%Coast% Yucatan% Pachón**' Molino**' Silvituc% Pacific% Tinaja**' Curva**' Figure'2a.' 'A.#mexicanus# Figure'1b' Crosses&A:& P' F1' Crosses&B:& P' F1' Crosses&C:& Figure'2d' P' F1' Surface% x Surface% 100%%see% Surface% x Molino% 100%%see% Molino% x Tinaja% Some%offspring% see% Molino% x Molino% 0%%see% Surface% x Pachón% 100%%see% Molino% x Pachón% Some%offspring% see% Belize% Figure'2c.'In%this%tree,%popula3ons%in%bold% with%**%include%blind%cave%fish% ' Pachón% x Pachón% 0%%see% Surface% x Tinaja% x Tinaja% 0%%see% Tinaja% 100%%see% Pachón% x Tinaja% Some%offspring% see% Q2. Blindness in Cave Fish Many populations of the blind cave fish A. mexicanus (Fig 2a) are known from different caves in North-­‐Eastern Mexico, including Molino, Pachón and Tinaja (Fig 2b). These fish, which may not have been exposed to light for 1 million years, evolved from eyed surface-­‐dwelling fish in the same area. Borowsky (2008) used different approaches to study whether blindness has evolved once, or multiple times: they constructed phylogenetic trees on the basis of the mitochondrial cytochrome b gene (Fig 2c) and performed genetic crosses to produce hybrid offspring which were tested for vision (Fig 2d). In previous research they discovered that eye development is determined by multiple genes. a. Based on the phylogeny in figure 2c, what is the minimum number of times that blindness has evolved? Explain your answer. b. Based on the crosses in Fig 2d, what is the minimal number of times that blindness has evolved. In your explanation, explain the results of Crosses A, then those of Crosses B and finally of Crosses C. c. What are two hypotheses for the evolution of blindness. Genotype!phenotype"in"blind"cave"fish"!"answers" Q2. Blindness in Cave Fish ! Q1."Genotype!phenotype"in"blind"cave"fish! in figure 2c, what is the minimum number of times that a. Based on the phylogeny ! blindness has evolved? Explain your answer. a. Based!on!the!phylogeny!in!Fig.!1c,!what!is!the!minimum!number!of!times!that!blindness!has!evolved?!Explain! The information preceding the question states that blind fish evolved from fish with visi your!answer.!! ! on. Hence, vision is the ancestral state. Because blind fish occur in two independent cla The!information!preceding!the!question!states!that!blind!fish!evolved!from!fish!with!vision.!Hence,!vision!is!the! des in which their closest relatives have vision, blindness has evolved at least twice. ancestral!state.!Because!blind!fish!occur!in!two!independent!clades!in!which!their!closest!relatives!have!vision,! blindness!has!evolved!at!least!twice.!! ! b. Based on the crosses in Fig 2d, what is the minimal number of times that blindness has b. Based!on!the!crosses!in!Fig.!1d,!what!is!the!minimal!number!of!times!that!blindness!has!evolved?!In!your! Crosses B evolved. In your explanation, explain the results of Crosses A, then those of explanation,!explain!the!results!of!Crosses!A,!then!those!of!Crosses!B!and!finally!of!Crosses!C.!! and finally of Crosses C. ! The!information!preceding!the!question!states!that!eye!development!is!determined!by!multiple!genes.!This!in! itself!suggests!that!different!mutations!may!result!in!blindness.!! ! The!results!from!crosses!between!surface!fish!and!cave!fish!at!each!location!(crosses!B)!suggest!that!blindness!is! a!recessive!trait,!because!100%!of!offspring!can!see.!This!is!also!confirmed!by!crosses!A,!in!which!crosses!between! blind!fish!within!each!location!never!result!in!fish!with!vision.!These!crosses!thus!tell!us!that!blind!fish!are! homozygous!recessive,!while!surface!fish!are!homozygous!dominant!(if!they!were!heterozygous,!only!half!of!the! offspring!would!have!vision).!!! ! Now!that!we!know!that!blindness!can!be!caused!by!several!genes,!and!that!blind!fish!are!homozygous!recessive,! we!can!analyse!crosses!C!in!more!detail.!All!these!crosses!are!carried!out!between!homozygous!recessive!fish,!yet,! in!each!case,!some!offspring!have!vision.!This!means!that!the!fish!at!the!different!locations!are!not!homozygous! recessive!for!the!same!locus.!Thus,!there!must!at!least!be!2!loci!involved.!Further,!because!each!pairwise!cross! results!in!some!offspring!with!vision,!we!know!that!each!population!must!be!different!(for!instance,!if!Molino!and! Tinaja!were!the!same,!they!would!not!together!produce!some!offspring!with!vision).!Therefore,!these!data! suggest!that!each!population!is!homozgous!recessive!for!a!different!locus.!This!suggests!that!blindness!has! evolved!independently!at!these!locations.!One!possibility!of!genotypes!at!the!different!locations!is!as!follows:! ! Molino P AaBbcc F1 Tinaja Molino AabbCc AaBbcc x Some!offspring! see AABbCc/AaBbCc x Pachón Pachón aaBbCc aaBbCc Some!offspring! see AaBBCc/AaBbCc x Tinaja AabbCc Some!offspring! see AaBbCC/AaBbCc ! ! c. Give!one!hypothesis!for!the!evolution!of!blindness.!!evolution of blindness. c. What are two hypotheses for the ! 1. Three!possible!hypotheses!are:! There is selection against eyes because their maintenance is energetically costly. 2. ! There is selection for other organs that come at the cost of producing eyes. For 1. example, it is possible that other sensory organs have developed that require the There!is!selection!against!eyes!because!their!maintenance!is!energetically!costly.!! ! 2. resources previously devoted to eye development. There!is!selection!for!other!organs!that!come!at!the!cost!of!producing!eyes.!For!example,!it!is!possible!that! 3. Because fish with eyes no longer have an advantage over fish without eyes, random other!sensory!organs!have!developed!that!require!the!resources!previously!devoted!to!eye!development.! ! genetic drift can result in the loss of them. (Note that we will talk about genetic drift 3. Because!fish!with!eyes!no!longer!have!an!advantage!over!fish!without!eyes,!random!genetic!drift!can!result!in! when we cover population genetics). the!loss!of!them.(Note!that!we!will!talk!about!genetic!drift!when!we!cover!population!genetics).! ! Source:!Borowsky!2008!Curr!Biol!18,!R23"24,!Niven!2008!Curr!Biol!18,!R27"29! Natural Selection: Practice Problem 3 Q3. Evolution in Darwin’s Finches Peter and Rosemary Grant have been studying darwin’s finches, and in particular, Geospiza fortis, since 1973, The Grants and their colleagues have monitored populations of this bird on Daphne major, a small island with a seasonal climate. Because the population is relatively small (~1200 birds), the Grants have been able to band almost every bird since the mid 1970s. On this island, the ground finches primarily eat seeds, which they crack at the base of the beak. Bigger beaks allow the eating of bigger seeds. The below data were collected from 1976 to 1978. There was a terrible drought on the island in 1977, which led to a dramatic decrease in the availability of small seeds. a. Which of the below figures (more figures on next page) provide evidence that individuals vary? b. Which of the below figures provide evidence that this variation is heritable? c. Which of the below figures provides evidence that not all individuals survive to reproduce? d. What evidence suggests that those individuals with favorable traits were more likely to survive or reproduce? e. What evidence suggests that evolution has occurred? Figure 1. Estimate of finch population size over time Note: Many birds were found dead. It is very unlikely that they left the island. Natural Selection: Practice Problem 3 cont… Figure 2. Finches born in the year before and after the drought Figure 3. Beak Depths in 1976 and 1978 Figure 4. Relationship of parent and offspring beak size Natural Selection: Practice Problem 3 Q3. Evolution in Darwin’s Finches Peter and Rosemary Grant have been studying darwin’s finches, and in particular, Geospiza fortis, since 1973, The Grants and their colleagues have monitored populations of this bird on Daphne major, a small island with a seasonal climate. Because the population is relatively small (~1200 birds), the Grants have been able to band almost every bird since the mid 1970s. On this island, the ground finches primarily eat seeds, which they crack at the base of the beak. Bigger beaks allow the eating of bigger seeds. The below data were collected from 1976 to 1978. There was a terrible drought on the island in 1977, which led to a dramatic decrease in the availability of small seeds. a. Which of the below figures (more figures on next pages) provide evidence that individuals vary? Fig 2-­‐4 all show that different birds have different beak depths. b. Which of the below figures provide evidence that this variation is heritable? Figure 4. c. Which of the below figures provides evidence that not all individuals survive to reproduce? Figure 1 d. What evidence suggests that those individuals with favorable traits were more likely to survive or reproduce? Above, I mention that the drought caused there to be few small seeds, and that this would favor birds with bigger beaks that could eat the remaining big seeds. In Fig. 3, we see the the population in 1978 consisted of more bigger bird beaks than the population in 1976 (before the drought), suggesting that the big beak birds survived the drought. e. What evidence suggest that evolution has occurred? Evolution is the change in a population over time. Figure 3 shows that the population shifted, and Figure 4 shows that this led to the population producing more big beaked offspring, so this shift is shaping/changing the population over time. Natural Selection: Practice Question 4 Leiocephalus carinatus (predator) Figure 4a Anolis sagrei (prey) Figure 4b Figure 4c Figure 4d Q4. Lizard predator and prey Anolis sagrei lizards (Fig. 4a) occur on small islands in the Bahamas. Leiocephalus carinatus are ground-­‐dwelling predatory lizards that do not naturally occur on these islands. Jonathan Losos et al. (2004) introduced L. carinatus lizards onto 6 islands where A. sagrei occurred (experimental islands); another 6 islands were studied as controls (no introduction of the predator). Introductions were done in May. The researchers first placed the predators in front of prey lizards to observe whether prey lizards climbed in trees to escape the predators (Fig. 4b); on the control islands the researchers put a control object, rather than a predator, in front of the prey lizards. The researchers then studied how habitat use of A. sagrei lizards changed over time. Fig. 4c shows the percentage of A. sagrei lizards found on the ground on experimental and control islands before (May) and after (Jul/Nov) introduction of the predator; Fig. 4d shows the average height in the vegetation used by A. sagrei in November. Using the data and information provided, answer the following questions. Assume that the prey population size did not change following introduction of the predator and that Anolis generation time is longer than 1 year. a. How does habitat use of the prey (A. sagrei ) differ during and after the introduction of the predator (L. carinatus)? b. Are the data more consistent with a behavioral change of A. sagrei (i.e., each lizard changes its own behavior), or with evolution by means of natural selection? Explain. c. Name three pieces of information that you would need to test whether changes in habitat use could be explained by means of evolution through natural selection. Explain. Natural Selection: Practice Problem 4 Q4. Lizard predator and prey Anolis sagrei lizards (Fig. 4a) occur on small islands in the Bahamas. Leiocephalus carinatus are ground-­‐dwelling predatory lizards that do not naturally occur on these islands. Jonathan Losos et al. (2004) introduced L. carinatus lizards onto 6 islands where A. sagrei occurred (experimental islands); another 6 islands were studied as controls (no introduction of the predator). Introductions were done in May. The researchers first placed the predators in front of prey lizards to observe whether prey lizards climbed in trees to escape the predators (Fig. 4b); on the control islands the researchers put a control object, rather than a predator, in front of the prey lizards. The researchers then studied how habitat use of A. sagrei lizards changed over time. Fig. 4c shows the percentage of A. sagrei lizards found on the ground on experimental and control islands before (May) and after (Jul/Nov) introduction of the predator; Fig. 4d shows the average height in the vegetation used by A. sagrei in November. Using the data and information provided, answer the following questions. Assume that the prey population size did not change following introduction of the predator and that Anolis generation time is longer than 1 year. a. How does habitat use of the prey (A. sagrei ) differ during and after the introduction of the predator (L. carinatus)? (4 pts) All figures indicate that in the presence of predators, the prey start using higher perches. This shift happens almost immediately. b. Are the data more consistent with a behavioral change of A. sagrei (i.e., each lizard changes its own behavior), or with evolution by means of natural selection? Explain. (8 pts) The information in the text above is important. It tells us to “assume that the prey population size did not change following introduction of the predator and that Anolis generation time is longer than 1 year.” Because of this, the predators have not eaten a substantial number of the prey on the ground and the population could not have evolved via natural selection because there has not been enough time for the favored trait (perching higher to escape predators) to be passed on. So these data are more consistent with a behavioral change. c. Name three pieces of information that you would need to test whether changes in habitat use could be explained by means of evolution through natural selection. Explain. (6 pts) Is perching height a heritable trait? Are predators more likely to eat those on the ground (i.e., is there differential survival)? Are predators eating prey that would have otherwise been able to reproduce? (not all individuals survive and reproduce) ...
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