Allometric dimorphism in the larvae of the salamander Hynobius retardatus

Abstract

Hynobius retardatus has a head-width plasticity that is functional in cannibalism and preying on large creatures. Cannibalistic specialization in H. retardatus appears to a lesser degree than in those species that have clearly dimorphic morphs. To examine the degree of cannibalistic specialization and intraspecific phenotypic variation, we investigated the allometric relationship between the head and body in the larvae of H. retardatus in a single pond. In addition, the effect of cannibalism on the determination of morphology was examined. A field survey revealed the existence of allometric dimorphism and the occurrence of large-headed large larvae. However, we did not observe a bimodal size distribution that indicates a split in the population. A laboratory experiment revealed that the development of such large-headed large larvae was inducible by actual cannibalism and/or additional tactile cues under high-density conditions. We deduce that the allometric dimorphism in the larvae of H. retardatus in the wild is caused by actual cannibalism. The cannibalistic phenotypic variation in H. retardatus would be characterized by allometric dimorphism without a bimodal size-frequency distribution.