Socioendocrine and morphological correlates of paternity in rhesus macaques (Macaca mulatta).

When females mate with several males, problems arise in identifying sire and in determining factors contributing to differential male reproductive success. Three potential primary correlates of differential reproduction in males include fighting ability, sperm competition, and body condition. We collected a variety of socioendocrine and morphological measurements from sexually mature rhesus macaques to determine corollaries of paternity. We studied a troop of about 150 rhesus macaques living in a 0.3 ha corral and identified the sires of 70% of infants using multilocus DNA fingerprints. Eight of 21 males sired offspring, and dominant males were more successful than subordinate males. Neither canine size nor age influenced the probability of siring offspring. Male reproductive success was primarily an outcome of the number of females mated with, which was associated with an ensemble of traits including high dominance rank, large body size, relatively voluminous testicles and good body condition. Testes size was significantly larger in sires than in non-sires, but among sires the number of progeny produced was not correlated with testicle size. Sires began the mating season with more body fat than non-sires, but the energetic costs of mating resulted in a 50% reduction in abdominal skinfold thickness during the mating season. We conclude that social status exerts a major impact on paternity by affecting the number of females mated with, that male quality is a critical factor modulating paternity, and that male feeding strategies have a direct influence on variation in male reproductive success.