Using a behavioral example of your choice, explain
how natural selection produces adaptation. Please describe clearly
the conditions that are necessary for natural selection to operate and
what the result is. Your example may be speculative (need not be supported
by data) but should be biologically plausible.
Briefly discuss the "proximate versus ultimate" approach
to questions about or explanations for behavioral phenomena. What specific
types of questions or explanations fall into each to these categories?
Briefly compare Tinbergen’s "four questions" with the "proximate versus
ultimate" dichotomy.
Bower birds (Family Ptilonorhynchidae) are a small group (15 species) of Australian birds that exhibit a unique and specialized set of breeding behaviors. Individual males construct a "bower", which is a carefully built pile of sticks and tree-bark, often glued together with saliva. The bower has a tunnel or chamber through or into which the female passes during her assessment of the bower. The male places a variety of objects such as colorful feathers or flowers, bone fragments, or pieces of colored glass near the entrance to the bower. Males’ bowers are typically placed in the center of a small (only a few square meters) symbolic territory, which contains only the bower and no resources that are attractive to females. The territories and bowers of several males are placed in close proximity. When females approach, males perform an elaborate vocal and visual display near the entrance to the bower. Females visit several males’ bowers in succession, and eventually choose one male as a mate based on the characteristics of his bower and his display. After copulation, females leave the cluster of bowers and return to a nesting and feeding area to lay eggs which they incubate on their own.
The species that are phylogenetically most closely related to bower birds have less specialized breeding behaviors. Males build nests out of sticks, bark, and other objects (including feathers and flowers) in territories that they defend against intrusion by other males. These territories contain feeding areas that females visit to forage. The territories are relatively large (many square meters), but the territories of several males are contiguous in areas of high habitat quality. At the beginning of the breeding season, males perform visual and vocal displays around the margins of their territories. During this period females visit several males’ territories, "shopping" for a male with an attractive display, well-constructed nests, and a high-quality territory. Females choose a male to pair with, and occupy a nest within his territory. Males with displays, nests, and territories of the highest quality may attract and pair with more than one female, each of whom has a nest within his territory. Males do no parental care but instead defend the territory against intrusion by neighboring males and females.
Unfortunately there are no extant species that exhibit intermediate stages between the "primitive" ancestral state and the "advanced" state exhibited by the bower birds. Briefly discuss a sequence of three possible evolutionary stages that might have occurred in the evolution of the bower birds’ breeding behavior from the ancestral condition (in other words, you have to speculate). Be sure to describe in sufficient detail the behavior of both males and females at each stage you propose, and make clear how each stage follows from the previous one.