Birth sex ratios relate to mare condition at conception in Kaimanawa horses

摘要: Several hypotheses have been proposed to explain variation in birth sex ratios, based on the premise that is expected when profitability of raising sons and daughters varies between individual parents. We tested Trivers-Willard hypothesis mothers better condition produce relatively more poorer male reproductive success variable. examined ratios relation mare body at conception horses which differentially helped by slight advantages condition. Horses meet assumptions than many species it has ratio biases are not confounded sexual size dimorphism such one likely die utero females poor Mares had a female foal were those foal, mares foals different sexes years significantly they conceived their foal. There was no relationship offspring mid-gestation condition, there difference foaling rates conception. Consequently, deviations explained fetal loss utero. Furthermore, differential less viable cannot greater proportion males produced Therefore, our results suggest modification occurs wild horses.