Population history of a hydrothermal vent-endemic gastropod alviniconcha hessleri in the Mariana trough

Abstract

Molecular evolutionary rate of the COI (cytochrome c oxidase subunit I) gene in the vent endemic genus Alviniconcha (Gastropoda: Provannidae) was estimated to be 0.69 % per million year based on GTR (General time-reversible) + G (Gamma) + I (Proportion Invariant) distances and hypothesized divergence dates of 59–64 Ma (million years ago) between Alviniconcha and its sister genus Ifremeria. The population history of A. hessleri, an endemic species to the Mariana Trough, the northwestern Pacific, was reconstructed by analyzing the nucleotide sequences of two fragments of mitochondrial DNA and an intron region of a nuclear gene for ATPS β (ATP Synthetase subunit β) and by extrapolating the estimated COI rate. Two genetically deviated A. hessleri groups with different patterns of geographical distribution were recognized in the analysis of the mitochondrial DNA and their age of divergence was estimated to be 0.91 Ma by the coalescent theory-based analysis of the nuclear gene data. The present geographical distributions of the two groups suggest that their ancestral populations were isolated in the central and southern Mariana Trough, respectively. Rapid expansion (increase of the population size) was suggested to have occurred in both groups at 0.26 and 0.17 Ma, respectively. Periodical changes of hydrothermal activity have apparently controlled the isolation and expansion of the local populations.