극피동물, 성게종들의 분자계통 및 종분화 시기 분석

Abstract

Sea urchins of the family Strongylocentrotidae have been important model systems in many fields of basic biology, yetknowledge of their evolutionary identities such as the phylogenetic relationships and divergence times remains limited.Here, I inferred molecular phylogenies of seven Strongylocentrotid species (Strongylocentrotus franciscanus, S. nudus,S. purpuratus, S. intermedius, S. droebachiensis, S. pallidus, and Hemicentrotus pulcherrimus) from the analyses ofmitochondrial DNA sequences of 12SrDNA (349 nt), 12SrDNA-tRNA(gln) region (862 nt), and a combined sequence ofcytochrome oxidase subunit I (COI, 1080 nt) and NADH dehydrogenase subunit I (NDI, 742 nt). The rate of sequenceevolution and divergence times for each species were then estimated from the trees with reference to the time ofseparation between Strongylocentrotidae and Parechinidae, 35 to 50 MYA. The three trees agree well with each other,and the phylogeny is summarized by ((S. franciscanus, S. nudus), (H. pulcherrimus (S. purpuratus, S. intermedius (S.droebachiensis, S. pallidus)))). It is notable that the genus Strongylocentrotus consists of two distinct clades and that H.pulcherrimus branches off within Strongylocentrotus, implying assignment of a separate, monospecific genus to thisspecies inappropriate. The rate of sequence evolution is calibrated to be 0.24%–0.34%/Myr in 12SrDNA, 0.25%–0.36%/Myr in 12SrDNA-tRNA(gln), and 0.65%–0.93%/Myr in COI-NDI combined sequences. S. purpuratus, in particular,shows the significantly higher rate of evolution in the 12SrDNA and 12SrDNA-tRNA(gln) regions compared to otherspecies, suggesting careful use of its sequences in comparative studies. The two clades of Strongylocentrotidae seem tohave split 13–19 MYA, and H. pulcherrimus branched off 7.2–14 MYA. In the former clade, S. franciscanus and S.nudus separated 5.7–8.1 MYA. In the latter clade, S. purpuratus, S. intermedius, and the clade of S.