• DOI:10.1086/285851
• Corpus ID: 85185475

Sexual Inequalities in Helminth Infections: A Cost of Being a Male?

@article{Poulin1996SexualII,
  title={Sexual Inequalities in Helminth Infections: A Cost of Being a Male?},
  author={Robert Poulin},
  journal={The American Naturalist},
  year={1996},
  volume={147},
  pages={287 - 295}
}

• R. Poulin
• Published 1 February 1996
• Biology
• The American Naturalist

Parasitism and its evolutionary relationship with host sex have received considerable attention in recent years. The role of parasites in maintaining host sexual reproduction (Hamilton 1980; Lively 1987; Ladle 1992) and in driving host sexual selection (Hamilton and Zuk 1982; Clayton 1991) has been explored theoretically and assessed empirically. One potential link between parasitism and host sex, however, has yet to be examined carefully. There are intrinsic biological differences between host sexes, differences that could lead to one sex being more prone to parasitic infections than the other. Although ost sex is often listed as a factor that can influence the parasite burden of individuals ( ee, e.g., Esch and Fern'andez 1993), statistically significant inequalities between female and male infection levels are not very common, and their direction is thought o depend on the particulars of the host-parasite system studied. There may be reasons (reviewed in Alexander and Stimson 1988; Bundy 1988; Zuk 1990) to expect one sex to be more heavily parasitized than the other. Physiological, morphological, and behavioral differences between females and males could operate to create a slight but consistent sexual bias in infection levels. For instance, high testosterone l vels can cause immunosuppression i males (Grossman 1985; Folstad and Karter 1992) and could lead to males in general suffering more from parasites than females do. Such a consistent bias may not be apparent from a scan of the literature on parasitic infections. Many parasite surveys have reported no significant differences between the prevalence or intensity of infection in female and male hosts, whereas others have found significant differences infavor of one or the other sex. However, many nonsignificant differences, if pointing in the same direction, can form significant trends when pooled and analyzed as a whole. Differences between the sexes may exist but be too marginal to be detected by examining a single host sample. The purpose of this note is to determine whether differences inlevels of infection between host sexes are random (i.e., normally distributed around a mean of zero) or biased in favor of one sex. To achieve this I analyze results of comparisons of helminth infections between female and male vertebrates, using data from the literature. Evidence of a bias in favor of one sex would suggest hat higher levels of parasitism may be a relative cost associated with that sex and could have a range of evolutionary implications.