In 1983, a population of dark-eyed junco birds became established on the campus of the University of California, San Diego (UCSD), which is located many miles from the junco's normal habitat in the mixed-coniferous temperate forests in the mountains. Juncos have white outer tail feathers that the males display during aggressive interactions and during courtship displays. Males with more white in their tail are more likely to win aggressive interactions, and females prefer to mate with males with more white in their tails. Females have less white in their tails than do males, and display it less often. (Pamela J. Yeh. 2004. Rapid evolution of a sexually selected trait following population establishment in a novel habitat. Evolution 58[1]:166-74.)
The UCSD campus male junco population tails were, on average, 36% white, whereas the tails of males from nearby mountain populations averaged 40-45% white. If this observed trait difference were due to a difference in the original colonising population, it would most likely be due to ________.
A) mutations in the UCSD population
B) gene flow between populations
C) a genetic bottleneck
D) a founder effect

Question

Quizplus · Accepted Answer

The observed difference in the trait between the UCSD population and nearby mountain populations is most likely due to a founder effect, which occurs when a small group of individuals colonize a new area and their genetic makeup differs from the larger source population. Mutations and genetic bottlenecks are less likely explanations for the observed trait difference. Gene flow could potentially affect the trait in the UCSD population if there was ongoing migration between the two populations, but the fact that the mountain populations have a consistent range of tail white suggests this is not the case.

In 1983, a Population of Dark-Eyed Junco Birds Became Established