Genetic architectures of postmating isolation and morphology of two highly diverged rockfishes (genus Sebastes).

Postmating isolation is thought to be an important driver of the late stages of speciation. However, relatively little is empirically known about the process compared with other isolating mechanisms that drive the early stages of speciation, especially in non-model organisms. We characterized the genetic architecture of postmating isolation between 2 rockfishes, Sebastes schlegelii and S. trivittatus, whose reproductive isolation is complete. We examined transmission ratio distortion (TRD) patterns of genetic markers in 2 reciprocal backcross populations. Markers showing either of the 2 types of TRD was widespread across the genome, with some of the distorted markers forming extensive clusters around the recombination coldspots. These suggest that the postmating isolation effectively prevents gene flow across the genome and the recombination landscape contributes to the genetic architecture. Comparisons between 2 backcross families and 2 developmental stages showed little similarity in the distorted markers, suggesting asymmetry and stage specificity of the isolation. This may be due to hybrid incompatibility involving maternal factors or extrinsic selection. The lack of sex-ratio distortion in the mapping families suggested that Haldane's rule in terms of hybrid inviability does not hold. Additionally, quantitative trait loci (QTL) mapping detected significant QTLs for sex and the morphological traits relevant to speciation and convergence of rockfishes, including body coloration. Genes in the melanocortin system, including agouti-signaling protein 1 (asip1) and melanocortin 1 receptor (mc1r), might underlie the horizontal and vertical color patterns on the body, respectively. These findings constitute an essential step toward a comprehensive understanding of speciation and morphological diversification of rockfishes.

An unexpected distribution record of the cold water fish Pholis fangi (Pholidae) from southern Taiwan.

Gunnel species (family Pholidae), characterized by an elongated bar-like body and usually found in shallow coastal waters, are mostly restricted to temperate to subarctic waters in the Northern Pacific Ocean, although some in the Western Pacific are distributed southward to the northern East China Sea. Despite the absence of previous records from subtropical and tropical waters, a single specimen of the fish family Pholidae was recently trawled off southwestern Taiwan. Examination on the morphological characteristics and DNA barcoding revealed this is a Pholis fangi (Wang Wang 1935), a species previously recorded only from cold waters in the Bohai and Yellow seas. As a consequence, the present specimen represents the first record of the species from the subtropical South China Sea coast of Taiwan, as well as an isolated southernmost record of this species, more than 1,000 km southward from the otherwise known distribution. Detailed morphology and fresh coloration are described.