Meeting Abstract

P3.72  Tuesday, Jan. 6  The relationship between parasitemia and resource allocation in Tachycineta bicolor LOCKHART, L.*; BONIER, F.; MUNRO, H.; MOORE, I.; ROBERTSON, R.; Queen’s University, Kingston ON; Queen’s University, Kingston ON; Queen’s University, Kingston ON; Virginia Tech; Queen’s University, Kingston ON 4ll14@queensu.ca

Within-individual trade-offs in resource allocation exist because of constraints and limitations on those resources. Because of these constraints and limitations, an individual may be forced to trade off between investment in immune system function, body condition, and response to environmental challenges, for example. However, we do not know how all of these functions are linked and what mediates the trade-offs that occur between them. Addressing this question will provide insight into how resources are allocated, particularly when an organism is confronted with environmental challenges. We examined the relationships between endoparasitemia in a free-ranging population of tree swallows (Tachycineta bicolor) and three measures of their resource allocation: white blood cell count, body condition, and corticosteroid levels. Results show that tree swallows with high parasitemia levels also had low body condition, a low heterophil: lymphocyte ratio, and a high corticosteroid level. These results suggest that in order to fight off parasite infection, tree swallows directed more energy toward their immune response and less energy toward maintaining body condition. Corticosteroid hormones, often considered an accurate measure of response to environmental stress in animals and known to play a role in immune responses, were elevated in birds with high parasitemia, and thus may play a role in mediating the trade-offs we observed. Our correlative findings provide evidence of the trade-offs that occur in organisms under stressful conditions. Further study is needed to determine the causal role that corticosteroids might play in mediating resource allocation.