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Abstract

Health of the mother is known to affect the sex-ratio of the offspring in sexually dimorphic mammals. Both density-dependent and environmental factors (conditions at present, or seasonal conditions the year before) could impact the health of the mother. There are however two opposing hypotheses for whether a mother in good health should invest more in a strong son (that can father many offspring) or in a daughter (that can stay in the same area and use good resources). Fetuses from 1,208 female white-tailed deer (Odocoileus virginianus) were collected over a 10-year period (2002-2012), across 75 counties in Arkansas. For each adult female deer, we estimated age, recorded live and dressed mass, calculated the kidney fat index (KFI), back-calculated the date of conception, and recorded the number and sex of fetuses. Our objective was to investigate whether female Arkansas deer that are in good health tend to produce more male or female fetuses, in addition to investigating which factors affect conception date in those same females. We developed a generalized linear model, with a binomial response (male versus female fetuses), to examine the effects of conception date, age and mass of the mother, number of fetuses, and KFI on fetal sex ratios. We found that mass of the mother had the greatest impact on fetal sex-ratios, with heavier females producing more male fetuses (β = 0.217 ± 0.008, P < 0.001). Female body condition (KFI) did not impact fetal sex-ratios. In addition, we developed a generalized model with mass of the doe, age of the doe, and an interaction between the two variables, to see how these physical properties influence conception date. We found a significant relationship between mass and conception date (β = -0.699 ± 0.190, P

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