Functional phenotypic plasticity of the endolithic mytilid Leiosolenus curtus (Lischke, 1874) (Bivalvia: Mytilidae)

Abstract

In Sagami Bay, Japan, Leiosolenus curtus (Lischke, 1874) bores into dead shells of rock barnacles (Tetraclita japonica) in Manazuru, calcareous sand-rock in Oiso, weathered tuff in Miura and agglomerates formed by the tubes of clam worms (Spirobranchus kraussii) in Kanaya. In order to understand the relationships between morphology and environment, the shell morphologies and genetic characteristics of L. curtus, together with the calcium content of the different bored substrata, were analysed. Individuals from Kanaya and Manazuru were characterised by a chalk-like encrustation and a more rounded and inflated shell shape, while those from Oiso and Miura had a striated encrustation. The molecular phylogenetic tree and haplotype network showed that the genetic sequences of the individuals from all investigated localities were very similar, and implied that they belong to the same species. The striated encrustation of the individuals from Oiso and Miura presumably enables them to scrape those residues not dissolved by the mucus secreted by the mantle gland, and thereby to bore into non-calcareous substrata. The more rounded and inflated shell shape of the individuals from Manazuru is thought to be advantageous for boring into thin substrata.