Ballentine, B. ., Smithsonian Institution, Washington, USA, ballentineb@si.edu
Greenberg, R. ., Smithsonian Institution, Washington, USA, greenbergr@si.edu

GENETICALLY-BASED MORPHOLOGICAL DIFFERENTIATION IN THE ABSENCE OF DIVERGENT NEUTRAL MARKERS IN SUBSPECIES OF THE SWAMP SPARROW: A COMMON GARDEN EXPERIMENT

The Coastal Plain Swamp Sparrow (Melospiza georgiana nigrescens) differs morphologically from conspecific populations in ways that are similar to other tidal marsh subspecies. However, Swamp Sparrows show no genetic structure in neutral markers. Many areas of tidal marsh are recent, post-glacial formations. However, in addition to being ephemeral in evolutionary time, tidal marshes present a profoundly divergent environment. Therefore, selection may have shaped adaptive differences even when colonization of a habitat is recent. Alternatively, local morphological differences may be the result of phenotypic plasticity. We tested the hypothesis that morphological divergence between tidal marsh and inland populations of Swamp Sparrow is the result of genetic differences using a common garden experiment. We found that morphological differences present in wild populations of coastal and inland swamp sparrows are maintained in lab-reared populations. These results support the hypothesis that morphological differences between populations are genetically based and suggest that natural selection is driving morphological divergence. A subspecies definition based primarily on patterns of divergence in neutral markers would miss the phenomenon of the evolution of adaptive traits in recently established populations.

Oral presentation

Session #:G14
Date: Tuesday, 8/5/08
Time: 10:30 AM

Presentation is given by student: Yes