The 82nd Annual Meeting of the American Association of Physical Anthropologists (2013)

The costs of seasonal reproductive effort in Cayo Santiago male rhesus macaques


Dept. of Anthropology, New York University (NYU)

Friday 9:00-9:15, Ballroom A Add to calendar

Males of seasonally breeding mammals incur specific seasonal costs associated with mating activity and competition. Our studies of male rhesus macaques on Cayo Santiago have aimed to elucidate these costs in a seasonally-breeding primate by integrating behavioral observations, physiological markers, morphometric variables, and life-history data. Here I synthesize these results to present an integrated picture of male seasonal reproductive costs. During the birth season, males have low androgen levels, and spend large proportions of time resting and feeding. This helps them build good physical condition, as assessed by high levels of urinary C-peptide of insulin (UCP), and high levels of body fat at the end of the birth season. During this time male mortality is low relative to female mortality. The mating season sees behavioral changes as males drastically reduce feeding and resting time to engage in mating activities, including consortships and serial mount copulations. These behavioral changes are associated with large increases in androgen levels and are demonstrably energetically expensive, with those individuals undertaking more mating exhibiting lower UCP levels. Rank instability during this period is rare, but when it occurs it brings specific costs to high ranking males, who experience elevated androgen and glucocorticoid levels compared to low ranking individuals. Probably as a consequence of these dynamics males experience high mortality relative to female mortality in the mating season; the inverse of the birth season relationship. These sex-specific costs of seasonal reproductive effort help to elucidate the basic differences in how male and female mammals compete.

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