A successful multiple litter adoption in a nursing southern black-eared opossum, Didelphis aurita (Didelphimorphia, Didelphidae)

Adoption by an alloparent of an offspring or a litter occurs in at least eight mammal orders, but is rare in marsupials, and was never confirmed in opossums. Here we report the first unequivocal and documented successful event of alloparental adoption of two distinct litters by a single captive female Southern Black-eared Opossum Didelphis aurita (Didelphimorphia, Didelphidae). The female, still nursing her biological litter, accepted and nursed the two offered litters. All three litters were raised simultaneously, and the female cared for and displayed protective behaviour indistinctively of the biological or adopted pups. She was kept captive until released along with her biological litter, which was weaned and fled independently, and the two adoptive litters clinging on her back. This event sheds additional light on the little known social and maternal behaviour of opossums, suggesting it is possibly more complex than originally thought.