Associations between first encounters and ensuing social relations within dyads of two species of lacertid lizards

Researchers often presume that dominant individuals, during an initial series of social interactions, ultimately gain possession of the territory, but detailed studies of the process of social relation establishment in animals are rare. We used an experimental approach on pairs of conspecific newborns of two lizard species (Podarcis sicula and P. melisellensis) to examine whether the outcomes of first encounters are consistent with the formation of social relations during the ensuing three weeks. A major objective was to determine whether social relations expressed during prolonged cohabitation induced divergence of individual growth rates within a dyad. Moreover, we explored to what extent individual differences in growth rate and behavior during social cohabitation paralleled differences expressed when the animals were housed in isolation. Differential expression of behavior within dyads was examined by calculating the difference between values for the two individual lizards. During brief first encounters, access to a localized basking site was determined by agonistic interactions between lizards. Cohabitation of two lizards during prolonged encounters resulted in differences in their thermal microhabitat usage, which in turn induced divergence of their growth rates. The direction and magnitude of the differences in thermal microhabitat use and the divergence in growth rates during prolonged encounters mirrored differences in the interactions exhibited during the first encounter. Moreover, differences between two lizards in initial social interactions, and in thermal microhabitat use and growth rate during prolonged encounters, paralleled differences in thermal microhabitat use exhibited when lizards were housed alone. Thus, it may be possible to predict the outcome of social interactions within dyads based on the differential expression of traits between two lizards housed in isolation.