Plasmodium infections of red-billed gulls (Larus scopulinus) show associations with host condition but not reproductive performance

Abstract

High prevalence of Plasmodium infection in some non-native bird species in New Zealand, coupled with distributional expansion of the introduced mosquito vector Culex quinquefasciatus, has raised concerns that immunologically naïve native species might be increasingly at risk from malarial parasites. We combined polymerase chain reaction (PCR) screening of archived blood samples with long-term field data of red-billed gulls (Larus scopulinus) at Kaikoura Peninsula to estimate the prevalence of malarial infection and its effect upon host condition and breeding success. Plasmodium prevalence assessed with PCR was 7.8±3.4%, 10-fold greater than estimates from microscopic analysis of blood smears (c. 0.7%, Tompkins et al. 2010). Phylogenetic analysis of parasite cytochrome b sequences isolated from red-billed gulls indicates that lineage RBG1 falls within a clade containing P. cathemerium morphospecies, whereas RBG2, isolated from a single individual, clusters with P. elongatum. We show that red-billed gulls infected with Plasmodium have bred at Kaikoura dating back to at least 1992, that chronic infections of lineage RBG1 are maintained over several years in some individuals, and that infection is associated with decreased body condition in breeding individuals of both sexes. There is currently no evidence that Plasmodium infection is associated with reduced breeding performance. However, further study involving the ecological context and temporal dynamics of infection is needed to assess cumulative effects on lifetime reproductive success.