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Precise, highly female-biased sex ratios in a social spider

Summary: Precise, highly female-biased sex ratios
in a social spider
Leticia Avile¨ s*
, John McCormack, Asher Cutter and Todd Bukowski
Department of Ecology and Evolutionary Biology, University of Arizona,Tucson, AZ 85721, USA
It has been recognized for some time that the risk of producing maleless clutches should select for a lower
than binomial variance in the sex ratio of organisms with female-biased sex ratios, small clutches and
breeding groups containing the clutch of a single female. However, to date, precise sex ratios have only
been reported for organisms with haplodiploid sex determination, a system which allows direct control of
the sex of individual oˇspring. In contrast, under heterogametic sex determination chance is expected to
play a crucial role in determining the sex composition of any one family, in particular when males are the
heterogametic sex. Here, we present evidence of precise or underdispersed primary sex ratios in the
Neotropical social spider Anelosimus domingo Levi. We show that this diplodiploid species with male hetero-
gamety has not only beaten the odds of meiosis by producing mostly daughters, but has also attained
relative precision in the proportion of sons and daughters produced in any one clutch. The latter ˘nding
suggests the existence of mechanisms that allow sorting of the two types of sperm in this spider species.
Keywords: sex-ratio control; sex-ratio bias; heterogametic sex determination; social spiders; Anelosimus
With heterogametic sex determination, chance is
expected to play a crucial role in determining the sex


Source: Avilés, Leticia - Department of Zoology, University of British Columbia


Collections: Environmental Sciences and Ecology