GLESENER, ROBERT R.. Ecology Program, Brevard College. Change in gene frequency in an urban eastern gray squirrel population.
Abstract: The city of Brevard NC hosts a non-albino white variant of the eastern gray squirrel. While pattern of inheritance is unknown, the two morphs appear to segregate as separate Mendelian units. In this study, I compare observed changes in gene frequency to that expected by various models. According to accepted chronologies, the white morph originated with the release of a pair in 1951. Assuming current squirrel abundance, the initial frequency of this predisposition ("white allele") would have been <.001. Today the percent of the white morph is holding steady at about 23.2%. If the "white allele" is recessive, then its frequency (q) is approaching 0.5 (0.482). A delta q of this magnitude requires a selective coefficient (s) of 0.85 or greater against the gray variant. If the "white allele" is dominant, its current allelic frequency (p=0.125) could be explained with s as low as 0.05, still against the gray morph. However, neither model explains the apparent equilibrium. The simplest equilibrium models invoke heterozygote advantage with homozygote dominant and recessive fitnesses being reduced by s and t, respectively. This would require some unseen pleiotropic effect. The model that best fits the data assumes that white pelage is dominant but that the gray homozygote has a higher fitness than the white homozygote (s=7t) but both being less fit then heterozygotes.
(A 15 minute oral presentation was given on March 24th as part of the
Zoology Session at the 2001 annual meeting of the North Carolina Academy
of Science held on the campus of the University of North Carolina at Greensboro.)