THE PARASITIC THEORY OF SEXUAL REPRODUCTION - PARASITISM IN UNISEXUAL AND BISEXUAL GECKOS

摘要

The parasitic theory of sexual reproduction was extended to account for the existence of unisexual higher vertebrates. Because unisexual lizards arose through hybridization of two sexual species, the hybrids' genotypes should be maximally heterozygous resulting in hybrid vigor. We therefore predicted that at least some unisexuals should be resistant to parasitism. To test the above prediction, we examined parasitism rates in a unisexual (Lepidodactylus lugubris) and a sexual gecko species (Hemidactylus frenatus) which live sympatrically on the island of Hawaii. Sixteen percent of the sexual geckos were found to have pseudotumors, 36% of the sexuals were infested with mites and the sexuals were also found to be susceptible to cestode, nematode and pentastomid infections. None of the unisexual geckos examined showed evidence of pseudotumor infection, mite infestation (even after they were housed with mite infested geckos) or cestode infections. The unisexuals were found to harbor pentastomids and nematodes although in the latter case the unisexuals were expelling adult nematodes in their faeces (an immune response to nematode infection). The above data lend support to our prediction that some unisexual species should be highly resistant to parasitism because they are maximally heterozygous. [References: 25]