PARENT SESSION

Genetics/Evolution 2 -- Session Chair: Jay Storz-- Nelson Hall East, Goodwin Forum

NATURAL SELECTION DRIVES ALTITUDINAL DIVERGENCE AT THE ALBUMIN LOCUS IN DEER MICE, PEROMYSCUS MANICULATUS. Jay F. Storz¹ and Jean M. Dubach². ¹ Department of Biology, San Francisco State University, San Francisco, CA, USA; ² Department of Conservation Biology, Brookfield Zoo, Brookfield, IL, USA.

ABSTRACT- In populations that are distributed across steep environmental gradients, the potential for local adaptation is largely determined by the spatial scale of fitness variation relative to dispersal distance. Since altitudinal gradients are generally characterized by dramatic ecological transitions over relatively short linear distances, adaptive divergence across such gradients will typically require especially strong selection to counterbalance the homogenizing effect of gene flow. Here we report the results of a study that was designed to test for evidence of adaptive divergence across an altitudinal gradient in a natural population of deer mice, Peromyscus maniculatus. We conducted a multilocus survey of allozyme variation across a steep altitudinal gradient in the Colorado Rockies that spanned several distinct biomes, from prairie grassland to alpine tundra. We used a coalescent-based simulation model to identify loci that deviated from neutral expectations, and we then assessed whether locus-specific patterns of variation were nonrandom with respect to altitude. Results indicated that the albumin locus (Alb) reflects a history of diversifying selection across the altitudinal gradient, as it was characterized by levels of altitudinal divergence that far exceeded neutral expectations in two consecutive years of sampling (in contrast to the pattern observed at unlinked loci). We conclude that clinal variation at the Alb locus reflects a balance between gene flow and diversifying selection that results from elevational changes in fitness rankings among alternative genotypes.

KEY WORDS: natural selection, altitudinal gradient, Peromyscus maniculatus, adaptation