Testosterone and Immunosuppression in Vertebrates: Implications for Parasite-Mediated Sexual Selection

Abstract

Females of many species prefer to mate with males that have the fewest parasites (Møller, 1990; Read,1990; Kirkpatrick and Ryan, 1991; Clayton, 1991; McLennen and Brooks, 1991; Clayton et al., 1992; Sullivan, 1991; Zuk, 1992). Females appear to discriminate among males on the basis of the expression of secondary sex characters, such as comb color and feather lenth in junglefowl (Gallus gallus) (Zuk et al., 1990), red plumage in house finches (Cardodacus mexicanus) (Hill, 1991); eye spot number on the tail-like train of peafowl (Pavo cristatus) (Petrie et al., 1991), or tail length in barn swallows (Hirundo rustica)(Møller, 1991). Experimental manipulation of parasite load can alter and hinder the expression of secondary sex characters (Zuk et al., 1990, Møller, 1991, Hillgarth, 1990). Therefore, females choosing males with well-developed secondary sex characters are likely to choose relatively parasite-free mates.