Effects of a haematophagous mite on the barn swallow (Hirundo rustica): a test of the Hamilton and Zuk hypothesis

Abstract

Tested 3 conditions of the Hamilton and Zuk hypothesis (1982), which suggests that the extravagant male plumage of many bird species allows females to choose mates that are resistant to the parasites exploiting the host population at a given time: 1) whether parasites affect the fitness of their hosts; 2) whether there is heritable variation in parasite resistance, and 3) whether the expression of the sexual ornament varies with parasite burden. The haematophagous mite Ornithonyssus bursa (Macronyssidae, Gamasida) sucks blood from their barn swallow hosts. Parasite burdens and origin, but not rearing conditions, of nestlings, affected their adult tarsus length and maximum body weight shortly before fledging. Mite loads of adult barn swallows at spring arrival were more similar to mite loads of their own offspring, whether reared in their own or in foster nests inoculated with mites, than to loads of foster offspring. Parents with long tail ornaments had offspring with smaller mite loads in partial cross-fostering experiments. The amount of increase in male tail ornaments from one year to another was negatively related to experimentally manipulated mite loads of nests during the preceding breeding season. The assumptions of the hypothesis were thus supported. -from Author