Meeting Abstract
P3.37 Saturday, Jan. 5 Impact of Winter Sex Ratio on Winter Physiology in a Differential Migrant the Dark-eyed junco O’NEAL, D.M.*; KILEY, R.; KETTERSON, E.D.; Indiana Univeristy; Indiana University; Indiana University daoneal@indiana.edu
Many studies consider the effect of sexual selection on the evolution of sex differences in behavior and physiology, particularly with respect to mating systems. Sex differences that arise by natural selection due to differences in a species� ecology are less widely appreciated. Sex differences in dispersal or migration can result in sexual segregation, and understanding why the sexes segregate can give insight into not only the evolution of sex differences, but also into population dynamics, responses to climate change, and ultimately the conservation of biodiversity. Many bird species exhibit sex differences in migratory distance traveled and a variety of hypotheses have attempted to explain this differential migration. In this study we evaluated the hypothesis that intrasexual competition for winter resources leads to differential migration by examining the effects of flock structure (sex ratio) on individual body condition and immune function in a differential migrant the Dark eyed junco (Junco hyemalis). In the junco, females migrate farther south than males, are behaviorally subordinate, and can be restricted from access to food by males. Male and female juncos were captured between late October and December 1st, during the junco�s autumn migration. Twenty-eight replicate flocks of 10 birds each were caged outdoors in identical compartments. Sex ratio was set at either 100% female, simulating conditions in the far south of the junco�s winter range, or 20% female, simulating conditions in the far north. Males and females were measured midwinter for differences in body fat, condition, innate immune measures (complement and IgG), and antibody production in response to injection with keyhole limpet hemocynin. Results will address the effect of winter population structure on male and female immune function.
