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Week5answers - Biology 180 Week 5 study questions Autumn...

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Biology 180: Week 5 study questions Autumn 2007 1. Squid are molluscs. Humans are vertebrates. a. Both have image-forming, camera eyes. Is this type of eye homologous in these species, or is it an example of homoplasy? Explain your answer. Because squid and humans are not closely related, and because other mollusks and vertebrates do not image-forming, camera eyes, the similarity is due to homoplasy. They result from convergent evolution, based on natural selection favoring the ability to see focused images. b. Both have a muscular heart that is involved in circulating body fluids. Is the presence of a heart homologous in these species, or is it an example of homoplasy? Explain your answer. Other mollusks and vertebrates have hearts, as do most species of animals that are closely related to mollusks and vertebrates. Thus, the traits are homologous. The trait is shared because it existed in a common ancestor. 2. Consider the following phylogeny of the mammal group called artiodactyls. |-------------------------artiodactyls--------------------------------| Carnivores Camel Pig Peccary Whale Hippo Cow Deer (dogs/cats/seals/bears) C ommon ancestor of whales & hippos Outgroup Common ancestor of all artiodactyls Root a) Identify and label: • the root of the tree • 3 monophyletic groups (many are possible) • the outgroup • the common ancestor of whales and hippos • the common ancestor of all artiodactyls b) N ame a shared, derived trait that helps identify the whales, dolphins, and porpoises as a monophyletic group. What logic did you use to support the hypothesis that this character is derived from a common ancestor? Many traits possible: aquatic habitat, streamlined bodies, lack of hind limbs, paddle-like forelimbs, etc.
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Other close relatives (e.g. other artiodactyls) lack these features and all are shared by whales, dolphins, and porpoises. c) Are the limbless, streamlined bodies of whales and dolphins homologous or due to homoplasy? Explain your reasoning. Homologous—they are similar because they were present in the common ancestor of these two groups. 3. Consider the phenomenon known as adaptive radiation. a) Give an example of an adaptive radiation. many possible answers b) How does your example fulfill the criteria given in the definition of an adaptive radiation? Needs to represent relatively rapid generation of many species from a single common ancestor, with descendants occupying many different habitats and using many different food sources. c) Suggest a hypothesis for why this adaptive radiation occurred. Why is this hypothesis plausible? Need to relate the radiation to an ecological opportunity, morphological innovation, or both. 4. Two populations of apple maggot fly have been identified. One lays eggs in hawthorn fruit; the other lays eggs in apple fruit. Fly larvae eat the fruit. Hawthorn and apple trees often grow side by side. Individuals from the two populations look identical but have distinctive genetic characteristics. Only about 5% of all matings occur between members of the two populations.
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