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Integrating Concepts in Biology II

Answer Key for Sample Exam covering Chs 19-21 on Evolution of populations/ecological systems

  1. (CH19) Explain why the data shown below support the hypothesis that flower color is being selected for in the plant “desert snow.” Elaborate in no more than 3 sentences and support using the data in the figures.

Flower color changes across the ravine, quite dramatically. None of the other four genetic loci (those not associated with flower color) change across the ravine, as evidenced by the frequency of the most common allozyme of each, suggesting no selection at those loci. The figure on the right shows that white plants on the white side of the ravine, at least in one year, have higher reproduction than blue plants on the white side, and in a different year the opposite was true. Even though there is variation among years, this is still evidence of selection and may have led to the pattern seen in the left figure, given enough time.

  1. (CH19) Use data fromData Gallery #1to explain how natural populations contain both drab and bright guppy males. Limit your answers to a maximum of 4 sentences.

Figure 19.3A: drab males inspect less when females are present, suggesting they hang back with the females. Figure 19.4: Females choose bold males no matter their coloration and there is not a perfect correspondence between boldness and color (FIGURE 19.3B).

  1. (CH19) Use data fromData Gallery #1to explain why someone could logically predict that only drab males would survive in a wild population. Limit your answers to a maximum of 2 sentences.

Figure 19.1 shows that timid (which is correlated with drab) fish survive longer.

  1. (CH19) Does boldness depend on presence of females? What evidence do you use to support your conclusion?Use data fromData Gallery #1to support your answer.

In the presence of female guppies, bright guppies are more likely than drab guppies to swim toward and inspect potential predators and bright guppies tend to be more bold (FIGURE 19.3).

  1. (CH19) Why do drab males inspect as much as bright males in the absence of females?Use data fromData Gallery #1to support your answer.

Drab males spent less time inspecting predators when females were present, because they spent more time near those females (FIGURE 19.3). These males may be more bold because they are paired with another male.

  1. (CH19) Is boldness correlated with color? What is your evidence, and what can you conclude about the strength of the relationship?Use data fromData Gallery #1to support your answer.

FIGURE 19.3B shows a strong correlation between color index and inspection frequency. While there is a fair amount of scatter in the relationship, the P-value < 0.005, indicating a significant relationship.

  1. (CH20) Of the two hypotheses constructed to explain the pattern of diversity in orchids, which is better supported? Use Data Gallery #1to choose the data testing each hypothesis and indicate how each hypothesis is well or poorly supported by the available data. Answer in no more than 2 sentences for each hypothesis.

Living in trees hypothesis is better supported than pollinator specialization.

The pollinator specialization hypothesis predicts that diversity arose through the process of specialization of pollinators. Subfamilies with higher numbers of species ought to have a lower mean number of pollinators/orchid species. The figure shows that there is not a conclusive relationship between the number of pollinator per species for a subfamily and the diversity of that subfamily. Subfamily A had the fewest number of pollinators per species but also the lowest species diversity, while subfamily E had a higher mean number of pollinators per species, and yet extremely high diversity. The hypothesis that highly specific pollinators would lead to higher species diversity is poorly supported (FIGURE 20.6).

The living in trees hypothesis predicts that the epiphytic condition of living in trees has led to diversity through an adaptive radiation. That is, an ancestral orchid evolved to live above ground and that allowed descendant species to further evolve to live in the wide variety of microhabitats that exist in the trees. The figure above on the left shows that, both among orchids and non-orchid plants, there were fewer genera with only 1 species per genus for tree-dwelling plants. There were several genera with more than 300 species per genus among the tree-dwelling orchids compared to no genera with more than 300 species for orchids on the ground. These data indicate that orchids living in trees have higher species diversity, supporting the hypothesis. The figures on the right merely show that that there are multiple microhabitats, some of which have more species, in the trees. It is not evidence for or against the “living in trees leads to diversity” hypothesis (FIGURES 20.4 and 20.5).

  1. (CH20) What might be the advantage to an epiphytic plant living in any one of the microhabitats found on a large tree? What might be a disadvantage that prevents more species and individuals from surviving in the microhabitat you chose?Use data fromData Gallery #1to support your answer.

Advantage of living further out or higher up in the tree is that the epiphyte can obtain more light (FIGURE 20.4). Possessing adaptations that allow small plants to live in trees provides them with high light conditions, as opposed to being small and living in the shade on the ground. Orchids and other plants with this adaptation are able to compete successfully for light, which may be limiting in forests. Although living at the very tops of trees might provide orchids with the highest light conditions, very few species live there. The disadvantages caused by high wind conditions, extreme daily temperature variations, and lack of support from weak branches may outweigh the advantages of high light. However, living high enough to gather light but gaining protection through a strong attachment to branches or trunks appears to be of benefit to individuals and their descendants.

  1. (CH20) Discuss one mechanism by which mosquitoes have been shown to evolve resistance to insecticides. Use Data Gallery #1 to choose the data that supports your answer. Explain the mechanism and how the data illustrate evolution of the mechanism in mosquitoes. Answer in no more than 3 sentences.

There are two mechanisms that we discussed. One is the modification, through adaptation, of a detoxification enzyme, and the other is modification, through adaptation, of a target site. TABLE 20.3 shows that Tanzanian mosquitoes are more resistant to DDT than Gambian mosquitoes. When examined for the mechanism of resistance, it was found that some variants of the enzyme GST was found in greater quantities in Tanzanian mosquitoes and that some of those variants were much more active in breaking down DDT than those in the Gambian mosquitoes. This latter point is important in concluding that evolution had occurred, and was probably caused by exposure to DDT(FIGURE 20.24).

TABLE 20.4 shows that a population of mosquitoes known to be resistant to permethrin had both altered detoxification enzyme and altered target site. When the enzyme that breaks down permethrin was inhibited by PBO, there was some increase in susceptibility to permethrin. However, that can’t be the only mechanism here, as they did not become as susceptible as the susceptible population. Permethrin and DDT have the same target site (but different detoxification enzymes break them down), so demonstrating that permethrin-resistant mosquitoes were also resistant to DDT is strong evidence that the target site has been modified.

  1. (CH20)Are A. gambiae from Gambia more susceptible to DDT than A. gambiae from Tanzania? What data support your conclusion? Use Data Gallery #1 to choose the data that supports your answer.

TABLE 20.3 shows that Tanzanian mosquitoes are more resistant to DDT than Gambian mosquitoes. The concentration that kills 50% or 90% of the population from Gambia is much lower than the concentration that kills 50% or 90% of the Tanzanian population.

  1. (CH19) Using data from Data Gallery #1, describe the evidence that evolution occurred in wild mustard due to a change in the climate. Support your answer with data and elaborate in no more than 3 sentences.

Focus on the data comparing plants from 1997 to those from 2004, especially in the plants from the wet soil population. Those plants, when exposed to dry conditions in the experiment, flowered earlier and had higher survival than their ancestral plants from 1997. During the drought between 2000 and 2004, the plant population evolved. There was less of a response in the 04 to 97 comparison of plants from the dry soil site, but it was still there. Plants growing there were already adapted to dry conditions, so were pre-adapted to the drought. The changes were adaptations for surviving and reproducing in a short wet season, and we also see that the changes are heritable. All this indicates that the drought placed selective pressure on the plants, causing them to adapt through natural selection to survive and reproduce in a dry climate (FIGURES 19.10 and 19.11 and TABLE 19.1).

DATA GALLERY #1

Figure 19.1
/ Figure 19.2

Figure 19.3
/ Figure 19.4

Figure 20.1
/ Figure 20.2

Figure 20.3
/ Figure 20.5

Figure 20.4
/ Figure 20.6

Table 20.3

Table 20.4

Figure 20.23
/ Figure 20.24
/ Figure 19.9

Figure 19.10
/ Figure 19.11

Table 19.1

  1. (CH20) What are the implications to susceptibility and resistance of differences in the mass of each GST variant? Would you predict some variants to play a larger role in resistance than others, and if so, which ones?Use Data Gallery #1 to choose the data that supports your answer.

Scientists discovered that the GST family of genes was responsible for conferring resistance to this population of mosquitoes. In the Tanzanian population, there was a greater amount of almost every GST enzyme, and some of those enzymes had much higher activity in the resistant than the susceptible population. Exposure to toxic chemicals can lead to increased expression of genes, as is evident for several variants, but the higher activity for the same variant in the Tanzanian population than the Gambian population indicates a mutation changed the allele to one that detoxifies DDT faster and may play a larger role in resistance (FIGURE 20.24).

  1. (CH20) If the enzyme that detoxifies permethrin is inhibited by PBO, what would you expect to observe in the permethrin w/ PBO treatment in Table 20.4? What do you conclude regarding the mechanism of resistance in this population of permethrin-resistant mosquitoes?Use Data Gallery #1 to choose the data that supports your answer.

There was evidence that PBO inhibition led to an increased rate of mortality and shorter time for 50% or 90% mortality, which suggested that the detoxification enzyme was inhibited (TABLE 20.4).

  1. (CH19) Interpret the p-values for Part A of the Figure 19.4, explaining what the p-values mean both statistically and biologically:

A p-value of 0.058 above the left pair of bars is above the cutoff of 0.05 used conventionally to reject a null hypothesis of no difference, thus we must conclude that while there may be a trend towards females choosing bright males that are simulated to be bold, we cannot conclude that females are displaying a preference here. For the right two bars the p-value is <0.01, and so we can reject the null hypothesis and conclude with pretty high confidence that females are selecting drab males when drab males are simulated to be bold and when a predator is present.

  1. (CH19) Using at least one of the figures below, discuss one consequence to genetic diversity for a species that has widely distributed,isolated, numerous, or small populations. Elaborate in no more than 2 sentences and support with data.

Populations that are small and isolated have greater genetic distance as geographic distance (Fig. 19.20) and as a consequence of that population structure, heterozygosity has decreased (Figs. 19.19 and 19.22) and alleles may be lost (Fig. 19.22). In small, isolated populations, genetic diversity often decreases through the processes of genetic drift or natural selection. Figures 19.19 and 19.20 are from the study of small plants widely distributed in the Swiss Alps, and Figure 19.22 is from the black grouse populations in Europe, where one population in the Netherlands has experienced a population bottleneck, in which alleles were lost due to random chance during a population crash. Combine that with isolation from other populations, and genetic diversity declines. The consequence of the types of population structures seen here is that genetic diversity can be lost, and that can lead to other consequences.

Figure 19.19 Figure 19.22

Figure 19.20

  1. (CH20)Compare the dates of existence of Paranthropus and Homo, using the horizontalwidths of the colored boxes in the evolutionary tree below, with the mammalian communities in Africa at 2 and 1.5 million years ago, shown in Figure 20.21. In what type of habitat was each of these hominid species living? Incorporate one of the following two themes of the Evolution Big Idea: Organisms can be linked by lines of descent from common ancestry, and natural selection is a mechanism of evolution that accounts for adaptation, into your answer.

Based on fossil evidence, scientists hypothesize that Paranthropus evolved about 3 MYA, followed by Homo around 2.5 MYA. The evolutionary tree shows that Paranthropus lived from approximately 2.8 to 1.3 million years ago (MYA), while Homo lived from 2.5 MYA to the present. Both coexisted for a period of time, but Paranthropus species went extinct about 1.6 MYA. Around 2 MYA, when multiple hominid species coexisted, the habitats in southern and eastern Africa included growing proportions of grazing mammals and declining proportions of tree-dwelling and fruit-eating mammals. This is evidence that the environment was changing from a more forested habitat to open grassland. If Paranthropus had evolved to live in trees or in forests, then the changing environment could have caused their extinction. Homo species might have lived in more open areas already, and when these habitats expanded as conditions became drier, these hominid species would have been favored by natural selection. Thus, a grassland environment likely favored Homo, as they survived and Paranthropus died off during this environmental transition. Natural selection acts as a mechanism of evolution, accounting for the adaptations (such as bipedalism and large brain).

Figure 20.21Figure 20.20

  1. (CH19) Choose three different scales-of-distance examples that illustrate a single mechanism of evolution that slows the rate of speciation. To get full credit, you must describe in general or name the species and how each figure is connected to this mechanism.Use Data Gallery #2 to choose the data that supports your answer. Limit your answers to a maximum of 2 sentences each.
  2. FIGURES 19.12 and 19.13: on the scale of 10s or 100s of meters this fungus can disperse to different rotting logs. Gene flow is the mechanism that slows the rate of speciation.
  1. FIGURE 19.17: on the scale of 10s of km this annual flowering plant can disperse to different geographic areas. Gene flow is the mechanism that slows the rate of speciation.
  1. FIGURE 19.18: on the scale of 1000s of km, European starlings can disperse across the country.Gene flow is the mechanism that slows the rate of speciation.
  1. (CH19) A loss of genetic diversity is a form of evolution.Use data fromData Gallery #2to support your answer.
  2. Give one example of a bottleneck effect. Explain why bottlenecks reduce genetic diversity. Support your answer with data. Limit your answer to a maximum of 2 sentences.

FIGURE 19.21 illustrates a bottleneck, where a population drops dramatically in abundance in a short time period. A bottleneck can be a form of genetic drift, where alleles are randomly lost from a population. TABLE 19.2 shows that genetic distance can be high when one population goes through a bottleneck compared to populations that have not experienced a bottleneck. FIGURE 19.22 shows that heterozygosity can be low and alleles can be lost in populations experiencing a bottleneck.

  1. Give an example of random loss of genetic diversity that is not the consequence of natural selection. Support your answer with data. Limit your answer to a maximum of 2 sentences.

TABLE 19.2 shows that genetic distance can be high when one population goes through a bottleneck compared to populations that have not experienced a bottleneck. FIGURE 19.22 shows that heterozygosity can be low and alleles can be lost in populations experiencing a bottleneck. While not known to be subject to a bottleneck, the plant species in FIGURE 19.19 have low heterozygosity, and these populations are small and isolated.While not known to be subject to a bottleneck, the plant species in FIGURE 19.19 have low heterozygosity, and these populations are small and isolated.

  1. (CH19)How does a “bottleneck effect” contribute to evolution? Use one specific example, name the mechanism of evolution, and support your example with at least two data sets. Use data fromData Gallery #2to support your answer.Limit your answers to a maximum of 4 sentences.

A bottleneck contributes to evolution by changing frequencies of alleles in a population, the definition of biological evolution. FIGURE 19.21 illustrates a bottleneck, where a black grouse population drops dramatically in abundance in a short time period. A bottleneck can be a form of genetic drift, where alleles are randomly lost from a population. TABLE 19.2 shows that genetic distance can be high when one population goes through a bottleneck compared to populations that have not experienced a bottleneck. FIGURE 19.22 shows that heterozygosity can be low and alleles can be lost in populations experiencing a bottleneck.