Under various ecological conditions, producing a biased sex ratio may be adaptive. However, the factors that translate specific ecological conditions into internal processes remain an enigma. A potential mediator is maternal testosterone, which may reflect physical, reproductive, and social conditions. The nutria (Myocastor coypus) is a polygynous rodent, invasive in many parts of the world, which shows fluctuating sex ratios. Using necropsies of 82 pregnant culled nutrias, we found that in early pregnancy, offspring sexratiosaremoremale-biasedthan inlater pregnancy. Sincesex ratios decrease with pregnancy age, male fetuses in our study population may be terminated. In 68% of the litters, the heaviest fetus was a male, suggesting that males are the Bexpensive^ sex. We also found that while maternal weight was not associated with testosterone, heavier females and those with lower testosterone had male-biased sex ratios. Litters of high testosterone females had female-biased sex ratios. To the best of our knowledge, this study is the first to show a negative association between maternal testosterone and male-biased sex ratios. Testosterone, through its role in reproduction, might be mediating maternal internal and external conditions by adjusting intra-uterine sex ratio. Significance statement For decades, the mechanisms behind offspring sex ratios have been of interest across
Behavioral Ecology and Sociobiology – Springer Journals
Published: Jun 1, 2018
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