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Reprod Fertil Dev. 2007;19(7):831-9.

Translocation reverses birth sex ratio bias depending on its timing during gestation: evidence for the action of two sex-allocation mechanisms.

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  • 1Centre for Biodiversity and Restoration Ecology, School of Biological Sciences, Victoria University of Wellington, Wellington 140, New Zealand.


Many sex allocation mechanisms are proposed but rarely have researchers considered and tested more than one at a time. Four facultative birth sex ratio (BSR) adjustment mechanisms are considered: (1) hormone-induced conception bias; (2) sex-differential embryo death from excess glucose metabolism; (3) sex-differential embryo death from embryo-uterine developmental asynchrony; and (4) pregnancy hormone suppression and resource deprivation. All mechanisms could be switched on by the corticoadrenal stress response. A total of 104 female rhinoceroses (Rhinocerotidae), translocated from 1961 to 2004 at different stages of gestation or conceived soon after arrival in captivity, were used to test for a reversal in BSR bias as evidence for the action of multiple sex-allocation mechanisms. Translocation induced a statistically significant BSR reversal between early gestation (86% male births from 0 to 0.19 gestation) and mid-gestation (38% male from 0.2 to 0.79 gestation). Captivity also induced a strongly male-biased (67% male) BSR for conceptions after arrival in captivity. The results indicate the action of at least two sex-allocation mechanisms operating in sequence, confirm the important role of sex-differential embryo death around implantation and of stress in sex allocation, and lend support to suggestions that sex-differential glucose metabolism by the preimplantation embryo likely plays a role in facultative BSR adjustment.

[PubMed - indexed for MEDLINE]
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