The mating system of callitrichid primates: I. Conditions for the coevolution of pair bonding and twinning

Callitrichids (marmosets and tamarins) are unusual among primates in having a particularly flexible mating system that spans monogamy, polyandry and polygamy, associated eith twin births and male parental care. The conventional assumption has been that monogamy evolved in order to allow the female to bear a litter of two relatively expensive young. An ESS approach is used to examine the costs and benefits of monogamy versus polygamy for the male and a litter size of one versus two offspring for the female in order to evaluate the conditions for the evolution of pair-bonded monogamy plus twinning. The results suggest that twinning could not have evolved before pair bonding in these species and that, all things being equal, it would always pay males to pursue a roving-male polygamy strategy. In response to this, females pursue a number of strategies that appear to be designed to coerce the male into remaining monogamous. © 1995.