Familiarity with adults, but not relatedness, affects the fitness of juvenile red-backed salamanders

Background/Question/Methods It is difficult to disentangle the relative roles of kinship and familiarity in affecting an individual's fitness. Not only is an individual more likely to have prior behavioral interactions with conspecifics in close proximity, it may also be related to those nearby conspecifics. While some studies have inferred that kin discrimination affects fitness, other studies have shown that familiarity alone can reduce aggressive interactions, thus increasing fitness. Prior studies attempting to disentangle familiarity and kin discrimination have focused on intra-age class pairs or groups despite many animals' opportunities for interactions with conspecifics from different cohorts. We examined juveniles of Plethodon cinereus, a terrestrial and territorial salamander, to determine whether their fitness increased by persisting in relatives' and/or familiars' territories, where they have greater access to food and moisture. We collected pairs of juveniles and adults found under the same cover objects in the forest (cohabitants) and pairs of juveniles and adults found under different cover objects, approximately 10 m apart (non-cohabitants). We determined parentage and relatedness of the adult-juvenile pairs and then placed these pairs in semi-natural mesocosms for 17 days. Results/Conclusions We found that juveniles housed with cohabitant adults had significantly greater increases in mass and snout-vent length than juveniles housed with non-cohabitant adults in 2006 but not in 2007, but relatedness did not affect growth. We also found no differences in relatedness between cohabitant and non-cohabitant pairs, implying that familiarity is not indicative of kinship. At least under certain environmental conditions, familiarity with adults, independent of relatedness or parentage, increased the fitness of juvenile salamanders.