EFFECTS OF A HAEMATOPHAGOUS MITE ON THE BARN SWALLOW (HIRUNDO RUSTICA): A TEST OF THE HAMILTON AND ZUK HYPOTHESIS

Abstract

Abstract.-I tested three assumptions 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. By choosing such males as mates, females will rear offspring carrying the genes for resistance. I tested three necessary conditions for the Hamilton and Zuk model: (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 Bam Swallow (Hirundo rustica) hosts. Experimental manipulation of mite loads and partial cross-fostering experiments on Bam Swallows, where half of the nestlings in the brood were exchanged with nestlings from another nest, shows that parasite burdens and origin, but not rearing conditions, of Bam Swallow nestlings, affected their adult tarsus length and maximum body weight shortly before fledging. Mite loads of adult Bam 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 offoster offspring. Parent Bam Swallows with long tail ornaments had offspring with smaller mite loads in the partial crossfostering experiments. The amount of increase in male tail ornaments from one year to another was negatively related to experimentally manipulated mite loads of Bam Swallow nests during the preceding breeding season. In conclusion, the three assumptions ofthe hypothesis were supported by the experimental tests.

Acquired resistance affects male sexual display and female choice in guppies

“…Many observational and experimental studies support Hamilton & Zuk's hypothesis by revealing a negative relationship between a male's parasite load and the showiness of his sexual characters (e.g. MÖller 1988MÖller , 1990Clayton 1990;Milinski & Bakker 1990;Zuk et al 1990a,b;Houde & Torio 1992;Saino & MÖller 1996; for reviews, see Clayton (1991) and MÖller & Saino (1994)). These same studies also provide evidence for a discriminatory preference of females for the showiest and least infected males.…”

“…heritable. Genetically based variations in immune response are well-recorded in experimentally controlled studies (Wassom et al 1974(Wassom et al , 1986Wakelin 1975;Wakelin & Blackwell 1988;MÖller 1990;Wakelin & Rose 1990;Wakelin & Apanius 1997). Most recorded examples are of continuous variation between extremes of resistance and susceptibility to parasites, although some examples are of discontinuous variation, where a host falls into one or another category.…”

Rapid evolutionary change in a secondary sexual character linked to climatic change

“…Long-tailed males enjoy several kinds of mating advantages, as demonstrated by observations and experiments (Møller, 1988(Møller, , 1994Saino et al, 1997). This secondary sexual character is condition-dependent because poor conditions in the winter quarters, ectoparasites and radioactive contamination cause the production of smaller characters (Møller, 1990(Møller, , 1992(Møller, , 1993. Long tails of males may improve manoeuvring ability (e.g.…”

Immunocompetence of nestling great tits in relation to rearing environment and parentage

“…In a correlational study, Boulinier et al (1997) found a positive relationship for tick load between parents and o¡spring. Strong support comes from MÖller (1990), who demonstrated in a cross-fostering experiment that mite populations on nestling barn swallows (Hirundo rustica) were partly determined by sibling relationships. Signi¢cant additive genetic variation in cell-mediated immunity was shown in nestling barn swallows by Saino et al (1997a).…”