Genetic structure, heterozygosity, and energetic patterns in wintering mallard and American wigeon populations on the southern High Plains of Texas

The objectives of this study were (1) to estimate the relative Wahlund effect observed within and among groups of mallards during migration into the wintering grounds of the Southern High Plains (SHP), and evaluate the relative accumulation of genetic information in the wintering population of mallards that migrate onto the SHP; (2) to determine if lipid reserves or body masses of mallards are correlated to multilocus genetic variation; (3) to determine if carcass component reserves of wintering American wigeon (Anas americana) are affected by demographic or environmental variables; and (4) to determine if carcass component reserves of wintering American wigeon are correlated to multilocus genetic variation.

Mallards (n=325) and American wigeon (n=643) were collected from the SHP of Texas from 15 October 1988 to 15 March 1989. Lipid and body masses were estimated for mallards. Body mass and masses of carcass components (lipid, protein, mineral, and water) were estimated for American wigeon. Mallards and American wigeon were surveyed electrophoretically for genetic variation at 30 and 25 loci, respectively.

Mallards and American wigeon had high levels of genetic variation compared to estimates for waterfowl or avian species in general. The genetic information obtained for wintering mallards exhibited a deficiency of heterozygotes (11.7%), which is indicative of the presence of a mixture of genetically heterogeneous populations in the wintering sample. Mallards carrying significant amounts of new genetic information arrived into the wintering area until at least the middle of December. Mallard populations may be structured genetically over their breeding range to a greater extent than has been previously thought.

Multilocus genetic variation was correlated negatively with body mass and carcass component reserves in mallards and American wigeon of different sex and age groups. This may indicate that birds with different genetic characteristics have different metabolic efficiencies or growth potentials. The relationships detected between genetic and functional characteristics in these wintering mallards and American wigeon are the first documented for any waterfowl species.

Carcass components of American wigeon varied significantly over the wintering period, and overwinter changes in carcass component reserves were different among birds of various sex and age groups. American wigeon of different sexes and ages maintain fat and protein reserves of proportionally different sizes, and use those reserves at different rates.