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Comments on Lo, Yun-Hua et al. (2015) International Worm Meeting "Sex-ratio bias in Caenorhabditis." (0)
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Lo, Yun-Hua, Hsu, Jung-Chen, Yang, Fang-Jung, Chang, Tiffany, Le, Son Tho, & Wang, John (2015). Sex-ratio bias in Caenorhabditis presented in International Worm Meeting. Unpublished information; cite only with author permission.
Most sexual species produce nearly equal sex ratios in their offspring. In nematodes, deviations from equal sex ratios occur in the self-fertile hermaphroditic species, which have evolved independently several times. Hermaphrodites produce predominantly hermaphrodite offspring, while sons are rarely observed, consistent with the high theoretical cost of male offspring in these species. In the genus Caenorhabditis, the three known hermaphroditic species also produce occasional males. When crossing occurs in C. elegans, the female-to-male offspring ratio is ~1:1, like most sexual species. In contrast, a previous study demonstrated that C. briggsae has a female-biased sex ratio (~2:1) possibly caused by competition between male X- versus O-bearing sperm.The female-biased sex ratios in C. briggsae may have evolved because of the probable advantages for fathers who produce more daughters, since a solitary hermaphrodite, but not son, can found a population. Alternatively, other conditions, such as local mate competition, may select for female-biased sex ratios. In the first model, only hermaphroditic species should have female-biased sex ratios, while in the second, female/males species could have female-biased sex ratios. To test these two possibilities, we conducted crossing experiments in the third hermaphroditic species, C. tropicalis, as well as 12 female/male species. We found that C. tropicalis produced an offspring sex ratio of ~1:1. For the female/male species, five exhibited ~1:1 ratios while seven others produced female-biased sex ratios. These results suggest that factors other than (or in addition to) hermaphroditism have selected for the evolution of female-biased sex ratios in this clade.
Affiliations:
- Biodiversity Research Center, Academia Sinica, Taipei
- Xuan mai, Chuong my, Hanoi, Vietnam