Document: JAC-3-46-3

Local adaptation in Colias butterflies along an elevational gradient: Consequences for reproductive isolation.

ELLERS, J.* and C.L.BOGGS

Stanford University, Stanford, CA 94305 USA ¹

Abstract:
Intraspecific divergence along sharp ecological gradients is thought to be a first step in the process of sympatric speciation. Local adaptation may lead to reproductive isolation without geographic isolation if two requirements are met. First, the characters that are under divergent selection should be genetically based and heritable. Second, these characters should be associated with characters involved in mate choice, so that migrating individuals have a reduced mating success compared to the resident, adapted phenotypes. We studied local adaptation in the butterfly Colias philodice eriphyle along an elevational gradient in the Colorado Rocky Mountains. Significant differences were found in life history and thermoregulatory characters among elevations. At high elevations, wing melanization increased compared to low elevation populations, which is consistent with the differences in environmental conditions. Laboratory experiments show that wing melanization has a high heritability of 76%. In field experiments, we showed that wing melanization is significantly correlated with mating success. In females in low elevation populations, we found a negative relationship between the number of matings and the degree of wing melanization. Also, individuals differing in wing melanization flew at different times throughout the day, thereby reducing the possibilities for mating. These results demonstrate that intraspecific divergence has the potential to increase reproductive isolation between Colias populations at different elevations.

Keywords: ecological gradient, local adaptation, reproductive isolation

This abstract is being presented at: 4:00 PM in session:
Oral Session #63: Evolutionary Ecology.