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生物代写|Knowing Nature – Homework 2



You end up in Trinidad (off the coast of Venezuela) and while walking in the woods you come across a stream with native guppies in them. Your friend points out two guppies (pictured on the right) – the individual above is a female, and below is a male.  Your friend says the following:

“You know, in some cases, females may favor mating with a male that is brightly colored simply because he is easy to locate visually. That would shorten the amount of time it takes to find a mate, and therefore reduce a female’s risk of being killed by a predator.”

You think this is interesting idea and makes plausible biological sense, but it doesn’t explain why males and females would be different; after all predation risk is something males face as well – with your friend’s logic why wouldn’t the female be brightly colored for the male to find her?

From what you know about biology, what theory would provide an alternative explanation for the much more elaborate patterning (and it turns out, also coloration) of the male?  AND: Why is it that the male is the showy one and not the female?

Briefly explain. (3pts)

You continue to walk along and notice a stream running down a hill. Different ponds exist along the stream. This seems to create geographically separated populations of the guppy species (scientific name P. reticulata).  In the upper pools males are strikingly colored and there are no predators of the guppies that live within the pool. In the lower pool, guppies are much more drab in color and pattern.

AND it turns out that  the main predator of guppies (C. alta), is a long-term resident species in the lower pool. Your friend hypothesizes that the guppies in the upper pool represent a case of warning coloration to potential predators that they are poisonous.  “Just look,” she says, “they are blue and have false eyespots on their bodies, whereas the lower pool guppies are a dirty tan and of low visual contrast.”

Why is your friend’s adaptive explanation very unlikely given the circumstances just described of the guppies in each population? AND: What is an alternative adaptive explanation for why the males differ in appearance the specific way they do in the two pools? (3pts)

You do a little experiment: you remove all the bright males from the top pool and replace them with drab males from the bottom pool.  What do you think might happen to the appearance of males in the upper pool population over evolutionary time (let’s say 20 generations)? Why?  Females of a similar type/genetic background seem to occupy both pools. (3pts)

2_Read the following news blurb on a scientific study:

Female Antarctic Seals Give Cold Shoulder to Local Males (February 14, 2007)

Scientists from the University of Cambridge and the British Antarctic Survey (BAS) studied a
colony of Antarctic fur seals (Arctocephalus gazella) on the subantarctic island of South Georgia. They discovered that female fur seals will travel up to 35 metres to find a mate…

It had long been assumed that the females were passive, simply mating with their nearest
male. However, using paternity tests, the scientists demonstrated that only a quarter of the
females conceived to their nearest male. The scientists believe that female fur seals may be able to assess male traits visually by examining body size and condition, dominant behaviours, or territory quality. Another possibility is that females can use smell to determine whether they are related to the male.

The news blurb claims that “It had long been assumed that females were passive, simply mating with their nearest male.”  Hmm. What do you make of this statement? What, if anything, might be the basis or rationale for such an assumption – logically, culturally, or otherwise?? (2pts)

The blurb says that perhaps females can smell if they are related to a male. Why would that be a useful ability to have?  Give an explanation in relation to evolution by natural selection, using the relevant reasoning/theories to connect to this claim. (2pts).