Geographic and individual variation in haematozoan infections in the greenfinch, Carduelis chloris

Abstract

Among- and within-population variation in prevalence and intensity of haematozoan infections was studied in blood samples taken from nine geographically widely separated greenfinch (Carduelis chloris) populations. Within populations, there were no consistent differences in prevalence between sexes or between older age-classes, but prevalence was significantly lower among yearling birds (<5 months old) in one population. Individual heterozygosity, as revealed by analysis of five polymorphic protein coding loci, did not differ between infected and noninfected birds. However, significant differences in prevalence between Fennoscandian (high), central European (low), and Iberian (high) populations is consistent with the hypothesis that destruction of natural habitats has led to a significant decline of vector populations in central Europe. Given the high among-populations variation in prevalence, our results point to the need to consider the possibility of sampling bias in studies that seek to test, using avian blood parasites, Hamilton and Zuk's hypothesis that parasite resistance might be the target of female choice and drive the evolution of bright plumage and elaborate ornamentation.