Mate Choice Near or Far

When strong positive heritability of fitness arises due to host-parasite coevolution, consequent sosigonic mate preference undermines monogamy through tendencies to extra-pair copulation. “Low” females bonded to “low” males try to parasitise their partnership by obtaining fertilization, surreptitiously if possible, from “high” males: correspondingly, in the case of birds, “Low” males may parasite by encouraging egg dumping in their nests by “high” females who have allowed copulation. It follows that nests of birds of low status should sometimes show evidence at times of both types of parasitism while nests of high status should show faithful monogamy. Rather differently from the argument in Hamilton and Zuk (1982), showiness in monogamous species is more likely to be related to such extra-pair objectives than to pair—bonding for nesting. Venereal disease makes males cautious about copulating with any female. Although prevented by true monogamy, when monogamy is partial, venereal disease may become the incentive for increasing female sexual advertisement. In extreme cases it may combine with other ecological factors to initiate sex role reversal, in which the female becomes the non-parenting sex of the species. As regards source of the heritability that backs the sosigonic selection assumed in such speculations, reasons are given for preferring a coevolutionary cycling of ancient, preserved, parasite-defense alleles to the alternatives of an abundant stream of good new defense mutations, or a process of elimination of purely deleterious mutations.