A biologist has been studying two populations of trout in Montana for the last 25 years, when the two populations were establish
ed from one common population. In the southern population, the fish now have a slightly different mouth shape. But the northern population hasn't changed from the original type. The new shape works well in catching the type of prey common in the habitat of the southern population. Which is the best explanation for the gene differences in the two populations?
The positive natural selection is a type of natural selection that increases the frequency of an allele or trait when it is advantageous for the population. What happened in the example is that the mouth with the slight change in morphology (trait) was more advantageous for the population in the south in relation to the ancestral morphology (still preserved in the population in the north), and therefore its frequency increased. This, in turn, is due to the fact that the food (prey) is not the same in the two habitats (north and south). The specific prey in the south, caused the new morphology to be selected, (increasing the frequency of individuals with the new mouth), becasue probably that trait allows the trouts in the south to hunt more effectively.
