RELATIONSHIPS BETWEEN GENETIC-VARIATION AND BODY-SIZE IN WINTERING MALLARDS

Mallards (Anas platyrhynchos; n = 282) wintering in the Southern High Plains (SHP) of Texas were collected from 15 October 1988 to 7 Februar y 1989. Lipid and fat-free body masses were determined for all Mallard s. Birds were surveyed electrophoretically for genetic variation at 30 biochemical loci. Our objective was to determine if structural size, fat mass, or fat-free mass of Mallards were related to multilocus gene tic variation. Wing-chord length, our estimator of structural size in Mallards, was shortest in female Mallards with the highest levels of g enetic variation. Fat mass and fat-free mass of Mallards (corrected fo r size) were not related to multilocus heterozygosity. Mixtures of mor phologically and genetically differentiated breeding populations of Ma llards on the SHP wintering area may explain the relationships between multilocus heterozygosity and size we detected in these birds.