Do blood parasites affect reproductive performance in male red bishops (Euplectes orix)? A test of the Hamilton-Zuk hypothesis

Abstract

According to the Hamilton-Zuk hypothesis of parasite-mediated sexual selection the expression of male secondary sexual characters as well as health and condition should be negatively affected by parasites. Over five breeding seasons we investigated the relationship between prevalence and intensity of blood parasites and reproductive performance as well as health state in male red bishops (Euplectes orix), a highly polygynous weaverbird species common in southern Africa. Neither prevalence nor intensity of infections with Plasmodium sp., the only blood parasite found in this study, were related to two important measures of male reproductive performance, i.e. the number of nests built (an intrasexually selected trait which is the most important determinant of male mating success) and the ability to establish a territory. In addition, parasite prevalence and intensity were not affected by season, time within season, age or body condition. These results do not support predictions derived from the Hamilton-Zuk hypothesis of parasite-mediated sexual selection. However, our data indicate that high stress levels as assessed by the heterophile/lymphocyte ratio might increase parasite susceptibility.