1. What does it mean to say that a particular phenotype has greater fitness than another phenotype?
The phenotype with greater fitness will contribute more offspring to the next generation than the other phenotype. Two important components of fitness are survivorship and fecundity. Review the Achondroplasia example, from Dr. Jones' lectures, which showed relative fitness of dwarves and normal sibs.
2. In lecture, Dr. Osenberg discussed three necessary conditions in order to get evolution via natural selection. What are those three conditions and why is each one necessary? Which of these conditions are unnecessary if we are, instead, interested in evolution via drift? (ignore this last question)
i) Variation in phenotype : Individuals must possess different traits. If all were alike, then there could be no difference in fitness among phenotypes.
iii) The phenotypes must differ in fitness : i.e., there must be selection. If there is no difference in survivorship and/or reproduction, there is no selection!
ii) These differences must be heritable : i.e., the effect
of selection must be passed on to the next generation. If the variation
in phenotypes does not have a genetic basis, but instead was produced by
phenotypic plasticity (i.e., an "environmental" effect), then
there would be no effect on the next generation despite the selection that
has occurred.
3. You go to two different sites (one "wet" and one "dry") and observe a particular "species" of lizard. Although the local herpetologist claims that these lizards all belong to the same species, you notice that the two populations have very different color patterns and head morphology. How would you determine a) if the variation in color pattern and head morphology was the result of an evolutionary change? and b) if these populations represented different species?
a) We are asking whether the difference in phenotype is due to a genetic difference, or to a plastic response to the environment? It would be most straightforward to grow animals under similar environmental conditions and then see if differences remain. E.g., You could perform a "common garden experiment" - bring the lizards into the lab -- after a couple generations (assuming you haven't imposed intense selection in the lab), see if the differences remain. If the stocks from the two populations remain distinct phenotypically, then the original differences were due to genetic differentiation.
Some of you suggested a reciprocal transplant study. This is a more elaborate version of the above scenario, and would be an excellent idea (assuming that you intended to rear offspring from both populations in both environmental conditions (i.e., the wet and the dry habitats)). This would provide you with something akin to a "norm of reaction" (the relationship between phenotype and environment for each genetic group). Thus, you'd be able to assess not only the effect of genetic differentiation and the environment, but also how much those two effects modified each other (e.g. whether each genetic group responded to the environment in similar ways: i.e., showed the same amount of phenotypic plasticity).
Some of you suggested looking at the fossil record. While this might be a useful approach, just observing a change in morphology is not sufficient to indicate evolutionary change. Bear in mind, that the change you observe in the fossil record could be caused by phenotypic plasticity. Under many scenarios, you can rule out this possibility, but ruling it out seems unlikely in this scenario (presumably, we're talking about relatively small differences between geographically isolated populations that may not even be different species yet).
b) Under the biological species concept, if these were different species, they would not be able to interbreed.
4. A veteran scuba diver has told you that she consistently observes three
species of sea urchin under the same types of coral heads on reefs in the
Florida Keys (i.e., the three species occur in the same habitats). Because
you are a BSC 2011 student, you know that urchins have external fertilization
and don't exhibit courtship. Your scuba diving friend wants to know what
keeps these urchins from interbreeding. What would you tell her, and how
would your answer change if you were discussing fishes with internal fertilization
?
A. Prezygotic isolating mechanisms: i) temporal- gametes released at different times or seasons; ii) gametic incompatibility- egg and sperm can't fuse. Postzygotic isolating mechanisms: Any could occur.
B. For fish species with internal fertilization: all of the above could still operate, plus: i) behavioral differences- no attraction; ii) mechanical differences- don't fit
5. Your lab partner has been studying fish in two lakes. He discovered that large mouth bass from the two lakes have very different jaw dentition. He was interested in determining if the difference in jaw dentition is genetically based. He therefore took bass from each population to Dr. Brazeau in the Zoology Department. Dr. Brazeau sequenced a portion of the DNA of these bass and found that the two populations were genetically distinct. Based on this information, your friend concluded that the differences in dentition represented a micro-evolutionary change. Dr. Brazeau cautioned him against making such an assertion. Why? What evidence would you suggest your friend collect?
The differences in DNA may not have anything to do with the differences in the teeth. We must first demonstrate that the differences in dentition are not just plastic responses to environmental differences. Hold the environment constant for several generations to see if the differences remain (as in Question 2 above).