22. Evolution of Populations

Which of the following statements regarding disruptive selection is true?

The graph below shows the birthweights and infant mortality rate as recorded by researchers in London between 1935 and 1946. The bars represent the number of births recorded in 0.5-pound increments. The orange dots represent the mortality rate for each birthweight and are shown on a logarithmic scale. What type of selection does this graph suggest directly affects human birth weight?

Graph adapted from: M.N. Karn and L.S. Penrose, Birth Weight and Gestation Time in Relation to Maternal Age, Parity, and Infant Survival. Annals of Eugenics, January 1951, Vol. 16 No. 1., Page 147-164.

The graph below shows the average tail length of a population of deer mice. The first graph shows the tail length of the mice while living in a prairie ecosystem, and the second shows the tail length many generations after a group of mice moved into a forest ecosystem. Which of the following types of natural selection describes this scenario, and what conclusion could you draw from these data?

In many species of salmon, there are two mating types in males: large aggressive males and small sneaker males. Large aggressive males fight for territory in which they mate with resident females, while small sneaker males hide and try to quickly enter larger males’ territories to mate with females. “Sneaking” is, on average, a more successful strategy when there are many large males competing for territory, while “Fighting” is, on average, a better strategy when there are few large males present. As described, this scenario describes what two types of selection?

Which of the following statements about frequency-dependent selection are true?

I. In frequency-dependent selection, the rare phenotype is favored.

II. Frequency-dependent selection leads to a loss of genetic variation over time.

III. Frequency-dependent selection is a form of balancing selection.

In a 1990 study on caribou by Barrette and Vandal in Behavioral Ecology and Sociobiology, it was observed that in confrontations between male caribou, the males with the larger antlers won 90% of the time. If this is a case of purely intrasexual selection, what else would you expect to be true?

Mudskippers, fish that leave the water to mate, perform elaborate dances involving jumping a few inches off the ground to attract mates. This is an example of: