Novel insights into adaptive evolution based on the unusual AT-skew in Acheilognathus gracilis mitogenome and phylogenetic relationships of bitterling.

ABSTRACT

Acheilognathus gracilis, a bitterling species, distribute in lower reaches of Yangtze River. They are identified as the top-priority bitterling species for conservation as having high evolutionary distinctiveness and are at risk of extinction. In present study, we first sequenced the complete mitogenome of A. gracilis and analyzed its phylogenetic position using 13 PCGs. The A. gracilis mitogenome is 16,774 bp in length, including 13 protein-coding genes, 2 ribosomal RNAs, 22 transfer RNAs, a control region and the origin of the light strand replication. The overall base composition of A. gracilis in descending order is T 27.9 %, A 27.7 %, C 26.1 % and G 18.3 %, shows a unusual AT-skew with slightly negative. Further investigation revealed A. gracilis uses excess T over A in NADH dehydrogenase 5 (nd5), whereas the most of other bitterlings are biased toward to use A not T, implying there is likely to be unique strategy of adaptive evolution in A. gracilis. We also compared 13 PCGs of 30 bitterling mitogenomes and the results exhibit highly conservative. Phylogenetic trees constructed by 13 PCGs strongly support the monophyly of Acheilognathus and the paraphyly of Rhodeus and Tanakia. Current results will provide valuable information for follow-up research on conservation of species facing with serious population decline and can provide novel insights into the phylogenetic analysis and evolutionary biology research.