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 colonizing 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 UCSD and nearby mountain populations is most likely due to a founder effect, as the UCSD population was established from a small subset of the original population. The smaller initial population may have had a lower frequency of alleles for white tail feathers, leading to a reduced frequency in the UCSD population.

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