THE ONTOGENY OF LITTERMATE PREFERENCES IN JUVENILE GOLDEN-MANTLED GROUND-SQUIRRELS - EFFECTS OF REARING AND RELATEDNESS

The social preferences of captive, juvenile golden-mantled ground squirrels, Spermophilus lateralis, were studied as a first step towards explaining the development of kin-differential behaviour, which occurs frequently in the genus Spermophilus. Three groups of young (four litters/group) were reared in the laboratory and then transferred as juveniles at about 36 days of age to an outdoor, semi-natural environment in which social interactions between juveniles were recorded. In group 1, littermates (young born to a common dam) were reared together until behavioural observations began. In groups 2 and 3, pups were cross-fostered between dams shortly after birth to examine how rearing (together or apart) and relatedness (littermates or non-littermates) affected juveniles' social interactions in the semi-natural environment. Social interactions were recorded for a 9-14-day period beginning when juveniles reached about 37 days of age, which coincides with when they would come above ground for the first time in nature. In all three groups, juveniles' social preferences were manifested most clearly in social play. In group 1, littermates (reared together) played together about twice as often as non-littermates (reared apart) on a per pair basis, which suggests that a shared rearing environment influenced the development of social preferences. In groups 2 and 3 in which pups had been cross-fostered, play-bout frequencies were ordered (high to low): littermates reared together>non-littermates reared together>littermates reared apart>non-littermates reared apart, and statistical analysis revealed that both rearing and relatedness contributed to this ordering. The sex of a pair also affected play-bout frequencies (M-M>M-F>F-F) independently of rearing and relatedness. Results from S. lateralis are compared with studies on other congeners, including parallel work on S. beldingi, in an effort to link interspecific differences in ecology and social organization to differences in the developmental systems that underlie the extent of kin favouritism in ground squirrels. (C) 1995 The Association for the Study of Animal Behaviour