Abstract
Starfish (phylum Echinodermata) are ecologically important and diverse members of marine ecosystems in all of the world's oceans, from the shallow water to the hadal zone. The deep sea is recognized as an extremely harsh environment on earth. In this study, we present the mitochondrial genome sequence of Mariana Trench starfish Freyastera benthophila, and this study is the first to explore in detail the mitochondrial genome of a deep‐sea member of the order Brisingida. Similar to other starfish, it contained 13 protein‐coding genes, two ribosomal RNA genes, and 22 transfer RNA genes (duplication of two tRNAs: trnL and trnS). Twenty‐two of these genes are encoded on the positive strand, while the other 15 are encoded on the negative strand. The gene arrangement was identical to those of sequenced starfish. Phylogenetic analysis showed the deep‐sea Brisingida as a sister taxon to the traditional members of the Asteriidae. Positive selection analysis indicated that five residues (8 N and 16 I in atp8, 47 D and 196 V in nad2, 599 N in nad5) were positively selected sites with high posterior probabilities. Compared these features with shallow sea starfish, we predict that variation specifically in atp8, nad2, and nad5 may play an important role in F. benthophila's adaptation to deep‐sea environment.
Highlights
The class Asteroidea is one of the most familiar and diverse groups of the phylum Echinodermata with a long paleontological history, including nearly 1,800 species grouped into 35 families (Clark & Downey, 1992; Matsubara, Komatsu, & Wada, 2004)
We found four overlaps: trnC/trnV, trnA/trnL1, atp8/atp6, and cox3/trnS2
We examined the potential positive selection in Brisingida lineage because of the colonization of deep-sea environments which may affect the function of mitochondrial genes
Summary
The class Asteroidea (sea stars and starfish) is one of the most familiar and diverse groups of the phylum Echinodermata with a long paleontological history, including nearly 1,800 species grouped into 35 families (Clark & Downey, 1992; Matsubara, Komatsu, & Wada, 2004) They are present in all of the world’s oceans and occur from intertidal to abyssal, and they are most diverse in the Indo-Pacific and tropical Atlantic regions (Mah & Blake, 2012). Animal mitogenome is typically always circular molecule, except for some classes of cnidarians (Bridge, Cunningham, Schierwater, Desalle, & Buss, 1992) It contains 37 genes in general: 13 protein- coding genes (PCGs) (cytochrome c oxidase subunits I–III [cox1- cox3], NADH dehydrogenase subunits 1–6 and 4L [nad1-6, nad4L], ATP synthase subunits 6 and 8 [atp, atp8], apocytochrome b [cob]), two ribosomal RNAs (12S and 16S), and 22 transfer RNAs (tRNAs). To infer the deep-sea adaptive evolution, positive selection analysis of mitochondrial genes was performed
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