Terms to know: optimality, convergent evolution, phylogenetic constraint (contingency), developmental constraint (contingency), phylogeny, comparative method

Questions:

1. Some evolutionary biologists have argued that most traits are optimally adapted to their environments.  Upon what do they base this argument?
2. Some evolutionary biologists have argued that trait evolution is constrained in some way, so that many traits are NOT optimally adapted.  What would prevent traits from being optimally adapted?
3. What is meant by a "phylogenetic contingency (or constraint)?"  By a "developmental contingency (or constraint)?"   Relate these ideas to the concept of correlated characters.
4. Why might a phylogenetic contingency (constraint) result in a species that is not optimally adapted to its environment?  Give a real or hypothetical example of a trait whose evolution has depended on phylogenetic contingency rather than on adaptation.
5. How should each of the following affect whether or not a species is optimally adapted to its environment: (a) the rate of  temporal change in the environment, (b) the degree to which the development of different characters is correlated.
6. For each of the following situations, answer the question about adaptation based on the phylogenetic information given as well as the descriptions of the traits. (Definition: monophyletic group = all the species that have evolved from one ancestral species). To practice interpreting and drawing phylogenies, also draw one or several phylogenetic trees to illustrates each situation.
1. Finches make up one monophyletic group, warblers make up a different monophyletic group.  All finches eat seeds and have thick bills; all warblers eat insects and have thin bills.  Does this provide good evidence for bill depth variation being adapted to diet type? Why/ why not?
2. Consider four different monophyletic groups of frogs.  Within each of four groups of frogs, some species climb trees have the ends of their toes expanded into structures that look like suction cups, while other species do not climb trees do not have expanded toes.  Does this provide good evidence that presence or absence of toe expansion is adapted to whether or not the frogs climb trees? Why/ why not?
3. Many plants that live in bogs (a kind of wetland habitat) have small leaves with hard outer coatings.  Studies of bog habitats suggest that such leaves may be functional in conserving water during times of the year when the bog is frozen.  These plant species are derived within several independent groups of plants; within each group, the  bog plants are each others closest relatives; their next closest relatives also have small leaves with hard outer coatings but do not live in bogs.  Does this provide good evidence that small leaves with hard outer coatings are adaptations to bog habitats? Why/ why not?
4. Kangaroos, kangaroo rats, deer, and ostriches live in habitats where as a result of predation and habitat structure, animals that can run or jump fast in a straight line survive best. These species all have reduced numbers of toes; studies of function of locomotion suggest that having fewer toes is more efficient for straight-line locomotion than is having more toes.  They are not closely related to each other; closer relatives to each species live in different habitats and have more toes.  Does this provide good evidence that toe reduction is an adaptation to allow rapid locomotion in a straight line? Why/ why not?
5. It is hypothesized that low frequency (low pitch) sounds are an adaptation to a need for long distance communication among individuals because low frequency sounds carry over longer distances than high frequency sounds.  This hypothesis predicts that the frequency of sounds should be inversely associated with the average distance between communicating individuals (i.e. species in which communicating individuals tend to be far apart should make low frequency sounds).  However, when this is graphed for the frog, bird, and mammal that vocalize, there is no apparent trend.  Does the lack of a trend falsify the hypothesis that low frequency sounds are an adaptation to long distance communication? Why/ why not?
7. For each of the following situations, suppose you are about to study the phylogeny of the group described to test an adaptive hypothesis, as described in the question.  To show how to test the hypothesis, draw the following phylogenetic trees: (1) a phylogenetic tree that would support the hypothesis by showing that the trait proposed to be an adaptation is derived and has evolved at the same time as the environmental trait to which is is hypothesized to be an adaptation, (2) a phylogenetic tree that would support the hypothesis presented by showing convergent evolution, (3) a phylogenetic tree that would not provide strong support the hypothesis, because it would suggest strong phylogenetic effects. NOTE: the strongest evidence of adaptation comes from a phylogeny showing both what is required by (1) and what is required by (2); can you draw such a tree (it would be an answer to both part (1) and part (2)).
1. Four species of mustelid mammal (weasels and otters) live in cold climates; in the winter they molt into white fur.  Three other species of weasel live in warm climates and do not molt into white fur in the winter. Hypothesis: molting into white fur in the winter is an adaptation to cold climates (it makes them cryptic in the winter when there is snow on the ground).
2. Four species of snake that feed on large prey have venom that breaks down tissue; four species of snake that feed on smaller prey have venom that kills prey but does not break down their tissue.  It has been shown that venom that breaks down tissue causes prey to be digested more rapidly and be less likely to rot.  Hypothesis: venom that breaks down tissue is an adaptation to aid digestion of large prey.
3. Three species of wasp lay their eggs in nests; in these species there are sterile workers.  Three species of wasp are parasitoids (lay eggs on another kind of insect; the larva develops in/on the insect host and ultimately eats it out from inside and kills it) that lay widely separated eggs; in these species there are no sterile workers.  Hypothesis: sterile workers are an adaptation (evolved through kin selection) that increases reproductive success of family groups in species that build nests.
4. Five bacterial diseases are highly virulent (harmful, likely to kill the host); four have low virulence (are not very harmful.)  The virulent diseases are all transmitted from host to host by insects; the four non-virulent diseases require direct contact between hosts.  Hypothesis: low virulence is an adaptation in diseases that are transmitted by direct contact between hosts, since high virulence in such species would result in low mobility, and death, of the host, so the disease would not be transmitted.
5. Three species of tree have large buttress roots that grow out of the side of the tree above ground, go into the ground, and apparently help support the tree.  Four species of tree lack these large buttress roots.  Trees with buttress roots occur in tropical rainforest where the soil is very thin so that roots cannot grow to any great depth; trees without buttress roots occur in temperate regions where soil is much thicker and the roots can grow deeper in the ground.  Hypothesis:  buttress roots are an adaptation to provide additional support and help prevent trees from falling in tropical areas with thin soil.