Kin discrimination and social behavior in communally -nesting degus (<italic>Octodon degus</italic>).

Abstract

In many species, individuals direct more affiliative behaviors toward genetic relatives than non-relatives. This nepotism occurs because individuals can increase their inclusive fitness by assisting relatives. In order to be nepotistic, however, one must be able to recognize kin. Most mammals recognize kin by the familiarity that develops as the result of sharing a common early rearing environment. Communally-nesting animals, however, share a rearing environment with close relatives and also non-relatives. I examined kin discrimination and nepotism in communally-nesting degus (<italic>Octodon degus</italic>). First, using a habituation method, I determined whether captive adult female degus in communal nests discriminated between the odors of pups that differed in their relatedness and/or familiarity to mothers. When pups were two weeks old (during lactation), mothers only discriminated the odors of related from unrelated animals, but when juveniles were six weeks old (post-lactation), mothers only discriminated the odors of familiar from unfamiliar animals. In a follow-up experiment, I used the transfer of radioactively labeled milk from mother to offspring to determine whether females sharing communal nests with either a sister or a non-relative would use their discriminatory abilities and preferentially nurse their own pups. Females preferentially nursed their own offspring when housed with a non-relative, but indiscriminantly nursed all pups when housed with a sister. I also examined whether juvenile degus display play partner preferences. By observing groups of juveniles in a semi-natural outdoor enclosure, I determined that juvenile degus prefer to play with familiar rather than unfamiliar agemates, and more closely-related (e.g. siblings) rather than more distantly-related (e.g. cousins) or unrelated agemates. Finally, I investigated how social behavior varies with genetic relatedness in free-living degus. A population of degus near Santiago, Chile was observed, and 6 DNA microsatellites were analyzed to determine genetic relatedness among individuals. Adult females exhibited foraging tolerance toward sisters, and preferentially shared burrows with them. Mothers and their offspring foraged in close proximity more often than unrelated female/juvenile pairs. Juveniles did not play more with siblings, but did play more with familiar burrowmates than unfamiliar non-burrowmates. These studies show that communally-nesting degus recognize relatives and display nepotism in certain situations.