The Effects of Kinship on Interactions between Tadpoles of Rana Cascadae

In a series of four field and mesocosm studies, we examined the effects of kinship on growth, survival, and aggregation behavior in tadpoles of the Cascades frog (Rana cascadae) under different ecological conditions. (1) Field observations of tadpole aggregations revealed ecological factors that may interact with kinship to influence tadpole interactions. (2) In an experiment conducted in mesocosms, food distribution, predator presence, thermal heterogeneity, and kinship all interacted to influence tadpole dispersion. (3) In a field experiment conducted in natural ponds, kinship significantly influenced group size at artificially established food patches. (4) In a field enclosure experiment, density, access to the substrate, and kinship all interacted to significantly influence growth and survivorship of tadpoles. Subsequent analysis revealed that kinship affected the distribution of individual tadpole body size: mass was more skewed (i.e., more small individuals) in groups of mixed relatedness than in kin groups. The interaction among kinship, density, and substrate factors resulted in context-dependent effects on tadpole size distribution and survivorship. Our results demonstrate that kinship factors can influence competitive interactions between tadpoles depending upon the ecological conditions, and they provide a functional explanation for kin-discriminating behavior observed in tadpoles of R. cascadae. Kinship-mediated competition may be particularly important for recruitment in size-structured populations.