Testing adaptive hypotheses of male reproductive cooperation

This study published last summer in Animal Behavior explores the potential for direct and/or indirect fitness benefits from reproductive cooperation among polyandrous males in Sanguinus geoffroyi (Geoffroy's tamarin). As observed in Geoffroy's tamarins, a single female mates with all adult males unrelated to her, and in turn the males cooperate to rear the young. Researchers studied six groups from two tamarin populations over 2-3 years, and determined that the polyandrous males were consistently more highly related to each other than expected by chance, and they often shared paternity both within litters and across the 2-3 year period. Groups with a single sire were also observed, which may be attributed to sperm competition. These findings suggest that both indirect and direct fitness benefits may play a role in the evolution of male reproductive cooperation.