남극성게, Sterechinus neumayeri, 의 진화과정

Abstract

The Antarctic sea urchin Sterechinus neumayeri is the most abundant regular sea urchin in shallow Antarctic waters showing circum-Antarctic distribution. Because of its abundance, easy availability and wide distribution, this organism has been used as a model system in many fields of the Antarctic biology. Yet, little is known about its evolutionary history and whether its evolution was correlated with separation of continents between the Antarctica and the South America. In the present study, an attempt was made to infer the molecular phylogeny of the Antarctic sea urchin in relation to the two southernmost South America sea urchins Loxechinus albus and Pseudechinus magellanicus and to compare the divergence time with tectonic events in the southern hemisphere. The phylogenies were reconstructed with mitochondrial DNA sequences of 12S rDNA-tRNA(gln) region (877nt) and cytochrome oxidase subunit I (COI, 1079nt) including not only the three species but also a species of Parechinidae Paracentrotus lividus and three species of Strongylocentrotidae Strongylocentrotus purpuratus, S. intermedius, and Hemicentrotus pulcherrimus. The phylogenetic trees reveal that L. albus and P. lividus form a closest relative cluster and S. neumayeri branches off from the lineage as a sister taxon. This group of three species makes a clear distinction from the species of Strongylocentrotidae. P. magellanicus comes as the most distantly related species. The divergence time of the species were estimated from the trees after the rate of sequence evolution was calibrated using the time of separation between Parechinidae and Strongylocentrotidae (35-50m.y.a.) as a reference time frame. The divergence between S. neumayeri and L. albus seems to occur 24-35 million years ago coincident with separation of the Antarctica from the South America. The result suggests that speciation of the Antarctic sea urchin must have been provoked by the tectonic event in this southern region.