Climate and maternal effects modify sex ratios in a weakly dimorphic marsupial

Delean, Steven, De'ath, Glenn, and Marsh, Helene (2009) Climate and maternal effects modify sex ratios in a weakly dimorphic marsupial. Behavioral Ecology and Sociobiology, 64 (2). pp. 265-277.

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There is growing evidence that the sex ratios of wild vertebrate populations are determined by mechanisms that are directly influenced by environmental characteristics. The Trivers–Willard (TWH) and extrinsic modification (EMH) hypotheses postulate differing determinants of mammalian offspring sex ratios. TWH states that mothers allocate resources according to their current condition and sex-specific offspring costs. EMH states that environmental forces that affect maternal condition determine offspring sex ratios, independently of maternal tactics of sex-biased allocation. We statistically assessed support for each of these hypotheses using long-term life histories of the allied rock-wallaby, Petrogale assimilis; a continuously breeding, polygynous, weakly dimorphic marsupial. We showed that birth sex ratios were equal and independent of maternal and environmental conditions. However, secondary sex ratios were male-biased under good environmental conditions and for high quality mothers or mothers in good condition. Sex differences in offspring survival contributed to these biases: (1) environmental conditions strongly influenced survival to pouch emergence (in support of EMH) and (2) maternal quality affected survival to the end of maternal care (in support of TWH). Environmental effects on survival were more important than maternal factors over the entire period of maternal care and contributed most to male-biased sex ratios at pouch emergence. In contrast, maternal mass was the best predictor of sex ratios at the end of maternal care—the life history stage where offspring body mass differed between the sexes.

Item ID: 10852
Item Type: Article (Research - C1)
ISSN: 1432-0762
Keywords: juvenile survival; El Niño; Southern Oscillation; maternal allocation; maternal quality; generalised linear mixed models; survival analysis
Date Deposited: 07 May 2010 03:00
FoR Codes: 06 BIOLOGICAL SCIENCES > 0603 Evolutionary Biology > 060303 Biological Adaptation @ 100%
SEO Codes: 96 ENVIRONMENT > 9608 Flora, Fauna and Biodiversity > 960806 Forest and Woodlands Flora, Fauna and Biodiversity @ 100%
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