Extraordinarily precise nematode sex ratios: adaptive responses to vanishingly rare mating opportunities.

Van Goor, Justin
Herre, Edward Allen
Gómez, Adalberto
Nason, John D
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Ecology, Evolution and Organismal Biology
Sex ratio theory predicts both mean sex ratio and variance under a range of population structures. Here, we compare two genera of phoretic nematodes ( and spp.) associated with 12 fig pollinating wasp species in Panama. The host wasps exhibit classic local mate competition: only inseminated females disperse from natal figs, and their offspring form mating pools that consist of scores of the adult offspring contributed by one or a few foundress mothers. By contrast, in both nematode genera, only sexually undifferentiated juveniles disperse and their mating pools routinely consist of 10 or fewer adults. Across all mating pool sizes, the sex ratios observed in both nematode genera are consistently female-biased (approx. 0.34 males), but markedly less female-biased than is often observed in the host wasps (approx. 0.10 males). In further contrast with their hosts, variances in nematode sex ratios are also consistently precise (significantly less than binomial). The constraints associated with predictably small mating pools within highly subdivided populations appear to select for precise sex ratios that contribute both to the reproductive success of individual nematodes, and to the evolutionary persistence of nematode species. We suggest that some form of environmental sex determination underlies these precise sex ratios.
This article is published as Van Goor, Justin, Edward Allen Herre, Adalberto Gómez, and John D. Nason. "Extraordinarily precise nematode sex ratios: adaptive responses to vanishingly rare mating opportunities." Proceedings of the Royal Society B 289, no. 1967 (2022): 20211572. Works produced by employees of the U.S. Government as part of their official duties are not copyrighted within the U.S. The content of this document is not copyrighted.
sex allocation, sex ratio variance, environmental sex determination, Ficus, Parasitodiplogaste, Ficophagu