MARTIN, LB*; HASSELQUIST, D; WIKELSKI, MC; Princeton University; Lund University; Princeton University: Immune function complements life history in tropical and temperate House Sparrows

Tropical passerine birds often lay small clutches, have long embryonic developmental periods, and high adult survival rates compared to related temperate species. Many ecological factors, particularly nest predation and food availability, have been hypothesized to influence these patterns, but strong evidence in support of these factors are lacking. We hypothesize that life history differences between tropical and temperate passerine birds arise in part because of among competing physiological systems. Specifically, we predict that Neotropical birds invest more in immune function than North-temperate birds, which would lead to smaller clutch size, longer development times, and higher survival rates because of the respective costs and benefits of a strong immune system. We tested this hypothesis by comparing multiple types of immune function in one species of bird, the House Sparrow (Passer domesticus), from one Neotropical (Panama) and one North-temperate (New Jersey) population. We found that sparrows from Panama tended to have stronger non-specific (innate) and antibody-mediated defenses than North-temperate sparrows, which instead had stronger cell-mediated immune defenses. Such immunological strategies in each population complement their expected life history differences; only the Neotropical sparrows invested in the most costly immune defenses.