Meeting Abstract

35.2  Wednesday, Jan. 5  Parasite release in an urban colonizer WILLIAMS, CK*; MARRA, PP; EZENWA, VO; BREUNER, CW; University of Montana; Smithsonian Migratory Bird Center; University of Georgia; University of Montana carin.williams@umontana.edu

Urban habitat is rapidly increasing worldwide, yet we know little about the effects of urbanization on wildlife. Despite diverse challenges presented by cities, many native species have managed to colonize urban areas. What makes these species successful? One answer may lie in the hypotheses of invasion biology. Natural enemy release from parasites seems particularly relevant to urban colonizers because cities should have strong effects on exposure to parasites and on host immune function. To test this hypothesis, I first examined malaria and ectoparasite infection rates in northern cardinals (Cardinalis cardinalis) sampled across an urban gradient. Next, I considered the mechanism through which parasite release may occur. If parasite release is caused by increased resistance to parasites, I expected investment in the immune system to increase in urban birds. Alternately, if parasite release is caused by decreased exposure to parasites, I expected immune system investment to remain the same or even decrease in urban birds. To test between these predictions, I compared bacteria killing ability, hemolysis, hemagglutination, and leukocyte distribution across the urban gradient. Early results demonstrate a decline in malaria and ectoparasite prevalence in urban birds, supporting the natural enemy release hypothesis. In addition, there was little change in immune parameters, suggesting that urban northern cardinals are released from parasites through decreased exposure rates, rather than increased immune investment.