Oryzias curvinotus in sanya does not contain the male sex‐ determining gene dmy

Abstract

Hainan medaka (Oryzias curvinotus) is distributed in the coastal waters of the South China Sea and is able to adapt to a wide range of salinities. In this study, we characterized O. curvinotus in Sanya River (SY‐medaka), which lacks dmy (a male sex‐determining gene in O. latipes and O. curvinotus). In a comparison of SY‐medaka and Gaoqiao medaka (GQ‐medaka), the morphological difference between the two populations does not reach the subspecies level and they can be considered two geographic populations of O. curvinotus. A mitochondrial cytochrome oxidase subunit I (CoI) sequence alignment showed that the sequence identities between SY‐medaka and other geographic populations of O. curvinotus are as high as 95%. A phylogenetic analysis of the mitochondrial genome also indicated that SY‐medaka belongs to O. curvinotus. Molecular marker‐based genetic sex assays and whole genome re‐sequencing showed that SY‐medaka does not contain dmy. Further, in RNA‐Seq analyses of the testis and ovaries of sexually mature SY‐medaka, dmy expression was not detected. We speculate that high temperatures resulted in the loss of dmy in SY‐medaka during evolution, or the lineage has another sex‐determining gene. This study provides a valuable dataset for elucidating the mechanism underlying sex determination in Oryzias genus and advances research on functional genomics or reproduction biology in O. curvinotus.