Litter sex

Pregnancy rates, litter sizes, and litter sex ratios vary strongly with the time in the estrous cycle at which female golden hamsters Mesocricetus auratus are mated. Early matings tend to produce relatively high pregnancy rates, large litters, and female-biased sex ratios, while late matings tend to produce low pregnancy rates, small litters, and male-biased sex ratios. Time of mating and litter size are therefore correlated, but each appears to have an independent effect on litter sex ratio: time of mating and sex ratio are positively correlated, holding litter size constant, while litter size and sex ratio are negatively correlated, holding time of mating constant. At each litter size greater than two, the variance of litter sex ratios is less than the binomial variance expected on the hypotheses of independent sampling with a constant probability of producing a male. The relationship between litter size and mean litter sex ratio is potentially consistent with several different models for the evolution of adaptive sex-ratio variation. This is a preview of subscription content, access via your institution.
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Litter sex composition affects life-history traits in yellow-bellied marmots

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Litter sex composition affects life-history traits in yellow-bellied marmots

When costs of producing male versus female offspring differ, parents may vary allocation of resources between sons and daughters. The model representing random Mendelian sex-chromosome assortment fit the data best; a homeostatic model received similar support but other models performed poorly. Such occasional significant patterns emphasize the importance of multi-season studies in distinguishing infrequent events from normal patterns. This is a preview of subscription content, access via your institution.
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The presence of siblings might have long-lasting fitness consequences because they influence the early environment in which an animal develops. Several studies under laboratory conditions have shown long-lasting consequences from the presence of male siblings in utero on morphology and life-history traits. However, in wild animals, such effects of litter sex composition are unexplored.
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Maternal care variations associate with DNA methylation of the glucocorticoid receptor gene, Nr3c1, in hippocampus at a nerve-growth factor-inducible protein 1 binding site. Epigenetic regulation of brain-derived neurotrophin factor is affected by early stress. These systems contribute to anxiety and fear.
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