Island and taxon effects in parasitism and resistance of Lesser Antillean birds

Patterns of parasitism in insular avian communities can provide insight int o processes that maintain host-parasite associations. On one hand, replicab le relationships within evolutionarily independent communities of the same host and parasite taxa would indicate that these interactions are stable ov er time. On the other hand, unique ecological conditions on each island, sp oradic colonizations and extinctions, plus new genetic variation would lead to island-specific host-parasite relationships. We examined the: distribut ion of three parasitic taxa among avian host species on three islands in th e Lesser Antilles: St. Lucia, Martinique, and Dominica. Blood protozoa of t he genus Haemoproteus were found in 34% of host individuals examined. A sig nificant species effect, but no significant island effect, was observed, su ggesting an ecologically stable and replicable host-parasite association. C ysts of the tissue-dwelling protozoan genus Sarcocystis were observed in 4% (9% on Dominica) of host individuals and were significantly associated wit h ground foraging. Epithelial lesions characteristic of avian papilloma vir us were recorded in 4% of host individuals on Martinique only. The pattern of infection with papilloma virus or Sarcocystis (significant island effect ) indicated that host species on a particular island are linked in transmis sion webs of these parasites. Such island-specific associations suggest a r ole for either history or unique local ecology in host-parasite association s. There was a statistically significant interaction between island and specie s effects in the prevalence of Haemoproteus. This may stem from the indepen dent evolution of host-parasite interactions in the different island popula tions. We were able to assess the extent of genetic divergence of the host species by analysis of mitochondrial ATPase 6,8 sequences. There was little genetic divergence between island populations of the host species. Therefo re, the variation in Haemoproteus prevalence is not likely to be related to genetic differentiation of the host populations. Birds infected with Haemoproteus exhibited elevated leukocyte levels indica tive of immunological control of the parasite. After statistically controll ing for the intensity of Haemoproteus infection and host species, leukocyte levels varied significantly among islands on which the host resided. This is consistent with the idea that insular avian communities are linked by tr ansmission webs of parasites having broad host specificity.