Abstract
AbstractWhen sons and daughters impart different fitness benefits, mothers should bias investment according to offspring sex, in some cases modifying offspring sex ratios. Sex allocation in monotocous organisms is expected to be costlier than for polytocous species, as it imposes a greater loss of reproductive effort in terms of mating and fertilization. Here, we show that variation in glucocorticoid concentrations around the time of conception predicts infant sex in a monotocous anthropoid, the black howler monkey (Alouatta pigra), suggesting that sex allocation is linked to a hormonal mechanism that affects early embryonic development. Glucocorticoids signal environmental conditions, and in our study, their variation was positively related to factors affecting infant survival. These results offer insight into sex allocation strategies in monotocous organisms.
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