Parasites and mate choice in red jungle fowl

Captive flocks of red jungle fowl (Gallus gallus) experimentallyinfected with the intestinal nematode Ascaridia galli were usedto test Hamilton and Zuk's (1982) hypothesis that parasitesadversely affect male secondary sex characters and that femalesprefer unparasitized over parasitized males. Infected chicksgrew more slowly than uninfected controls, with the effect particularlypronounced on comb length rather than tarsus length or bodyweight. At sexual maturity, infected roosters had duller combsand eyes, shorter combs and tail feathers, and paler hacklefeathers than control roosters. In experimental mate choicetests, females preferred unparasitized over parasitized roostersby about 2: 1, and an analysis of covariance revealed that thehens were using the traits on which the two groups differedto make their mate choice decisions. Finally, in a test of anextension of the Hamilton and Zuk hypothesis, control and infectedmales were not distinguishable based on non sexually-selectedcharacters such as bill size, suggesting that parasites havea disproportionately larger effect on ornamental traits.