Kinship ecology of competition: size hierarchies in kin and nonkin laboratory cohorts of tadpoles.

This study provides an experimental test of the ecological significance of kinship in competitive interactions among individuals. Tadpoles of the fire-bellied toad, Bombina variegata (Anura, Discoglossidae) reared in the laboratory in a high density of siblings grew better and developed faster than when they were reared with similar densities of nonrelatives. Kinship-based genotypic uniformity may therefore be advantageous: it can lead to faster and more uniform growth. In nature it may well be kin recognition that permits such advantage to be realised. The largest tadpoles from pure-sibship cohorts accounted, on average, for the smaller fraction of the cohort total biomass than the largest tadpoles reared with cohorts of nonrelatives, although they attained the same absolute weight and developmental stage. The smallest individuals from pure-sibship cohorts had a much larger absolute body weight than the smallest tadpoles from mixed-sibship cohorts, and were also much more advanced developmentally. The results could be an effect of an altruistic restraint in growth rate on the part of the largest tadpoles in sibling cohorts and certainly not of the smallest ones. However, the results could also be due to the altruism-independent facilitation of living conditions in pure-sibship groups, resulting solely from potential advantages of homogeneous water conditioning.