Facultative adjustment of mammalian sex ratios in support of the Trivers–Willard hypothesis: evidence for a mechanism

Evolutionary theory predicts that mothers of different condition should adjust the birth sex ratio of their offspring in relation to future reproductive benefits. Published studies addressing variation in mammalian sex ratios have produced surprisingly contradictory results. Explaining the source of...

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Bibliographic Details
Published in:Proceedings of the Royal Society. B, Biological sciences Biological sciences, 2004-08, Vol.271 (1549), p.1723-1728
Main Author: Cameron, Elissa Z.
Format: Article
Language:English
Subjects:
Age Factors
Animals
Biological Evolution
Blastocyst
Body Constitution
Conception
Daughters
Female
Glucose - metabolism
Glucose - physiology
Litter Size
Male
Mammalia
Mammals
Mammals - physiology
Maternal Investment
Mating behavior
Models, Biological
Mothers
Pregnancy
Reproduction - physiology
Seasons
Sex Allocation
Sex Factors
Sex Ratio
Sons
Time Factors
Trivers-Willard Hypothesis
Ungulates
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Summary:Evolutionary theory predicts that mothers of different condition should adjust the birth sex ratio of their offspring in relation to future reproductive benefits. Published studies addressing variation in mammalian sex ratios have produced surprisingly contradictory results. Explaining the source of such variation has been a challenge for sex-ratio theory, not least because no mechanism for sex-ratio adjustment is known. I conducted a meta-analysis of previous mammalian sex-ratio studies to determine if there are any overall patterns in sex-ratio variation. The contradictory nature of previous results was confirmed. However, studies that investigated indices of condition around conception show almost unanimous support for the prediction that mothers in good condition bias their litters towards sons. Recent research on the role of glucose in reproductive functioning have shown that excess glucose favours the development of male blastocysts, providing a potential mechanism for sex-ratio variation in relation to maternal condition around conception. Furthermore, many of the conflicting results from studies on sex-ratio adjustment would be explained if glucose levels in utero during early cell division contributed to the determination of offspring sex ratios.
ISSN:0962-8452
1471-2954
DOI:10.1098/rspb.2004.2773