1. Referring to the cladogram on page 1 and with regard to mono- / polyphyly, vertebrates are a monophyletic group; invertebrates are parayphyletc.

Transcription

1 Answers III.4. Animals-I. 1. Referring to the cladogram on page 1 and with regard to mono- / polyphyly, vertebrates are a monophyletic group; invertebrates are parayphyletc. 2. Referring to the cladogram on page 1, which of the following traits arose just once? a. Coelom b. Limbs c. Pseudocoelom d. Radial symmetry e. Segmentation 3. Referring to the cladogram on page 1, the acoelomate condition of flatworms is a(n) derived trait. 4. The mass of cells that results from division of the original fertilized egg is called a blastula. A gastrula results when the blastula invaginates. 5. If all animal limbs really are homologous (as opposed to the genes that control their development), cephalochordate ancestors must have lost their limbs. 6. SJS patients often require intubation. Why? (You may have to look up intubation. ) The lining of the throat derives from embryonic ectoderm. It becomes in-

2 flamed, swells and the patient is unable to breathe unassisted. Hence the need for a breathing tube. 7. A general evolutionary trend among animals has been increased size and complexity. What would Lamarck have had to say about this? What would Darwin have said? Be brief. (Not covered in lecture) Lamarck would have approved, citing the Power of Life. Darwin would have suggested that, while greater complexity is often favored by natural selection, there are many cases in which it is not. 8. Baleen whales are huge; their prey, tiny. Most predators that eat small prey are themselves small. Why? The smaller your prey relative to your needs, the more you have to catch and eat. Crudely, and absent some sort of efficient sieving device, you want to eat the largest prey you can handle. 9. Strategies that have been employed in the fight against malaria include the following: a. insecticides; b. draining ponds and marshes; c. anti-malarial drugs; d. window screens; e. bed nets often impregnated with insecticide. Which of these target(s) the larval stage? a. if the target is bodies of water; b. 2

3 10. The classifications / phylogenies given in this lecture are quite different from those that your instructor learned way back when. What principal development(s) might have caused the changes? a. Advent of molecularbased phylogenies. b. Adoption of cladistic methodology. 11. In many social hymenoptera (ants, bees), workers (all diploid females) are generally sterile. In these species, males are haploid. From an evolutionary point of view, how might these observations be related? (Requires outside reading.) Imagine for argument s sake that the species in question has a single pair of chromosomes. Call Dad s single chromosome XM, and call Mom s two chromosomes XF1 and XF2. Females, all sisters, have two chromosomes, and their genotypes will either be XMXF1 or XMXF2. If we average over many females, the average number of genes any two will have in common is 75%, i.e., they all get Dad s chromosome and there is a 50% chance that they get the same chromosome from Mom. 3

4 By way of contrast, females only have 50% of their genes in common with their own female offspring, to which they and the male with which they mate each contribute a single chromosome. New queens are their sisters this is critical. So the workers should forego reproduction in favor of feeding the existing queen and nurturing her female offspring, some of which will become new queens. 12. Regarding your answer to #11, how would your answer be affected by the observation that queens often mate with multiple males? Likewise, how does sex determination in termites affect your argument? (Requires outside reading.) Queens store sperm in a special structure called a spermatheca. If Mom mates more than once, her reproductive offspring may not be your full sister. Termite males are diploid, so the argument given in the answer to Question 12 doesn t apply. Nonetheless, termite colonies are organized in much the same way as the nests of social hymenoptera, i.e., only the queen lays eggs. From this, we conclude that haplodiploidy may be sufficient to for the evolution of sterile workers, but it is not necessary. 4

5 In fact, not all hymenoptera are social, this despite the fact that all hymenoptera have haplodiploidy sex determination. It follows that haplodiploidy isn t sufficient for the evolution of worker sterility either. What one is left with is the weaker, and far less satisfactory, assertion that haplodiploidy appears to increase the likelihood that sociality and worker sterility evolve. 5

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