Cross-fostering experiments

Within 24 h of birth, we exchanged pups from one species (P. polionotus or P. maniculatus) with pups of the other species that were also born within 24 h. In no case was there any obvious rejection of the pups. We weaned cross-fostered pups at 23 days of age with pups of their biological species in cages of five animals of the same sex, in the same way as non-cross-fostered animals. At 60–90 days old, we paired cross-fostered animals with an animal of their own biological species (cross-fostered or not) and tested parental behaviours as described above. Number of litters cross-fostered animals represent: P. polionotus mothers: 8; fathers: 9; P. maniculatus mothers: 9; fathers: 7.