Sebastes pachycephalus

Kai, Yoshiaki & Nakabo, Tetsuji, 2013, Taxonomic review of the Sebastes pachycephalus complex (Scorpaeniformes: Scorpaenidae), Zootaxa 3637 (5), pp. 541-560 : 556-557

Hybrids between Sebastes pachycephalus and S. nudus

Materials examined. 5 specimens, 119.0– 173.2 mm SL, all from Japan: FAKU 6319, 119.0 mm SL, Shimonoseki, Yamaguchi; FAKU 41980, 173.2 mm SL, Maizuru, Kyoto; FAKU 85922, 86957, NMCI–P. 1527, 122.7– 128.8 mm SL [3 specimens; all genetically identified as hybrids in Kai et al. (2011)], Noto, Ishikawa, coll. Y. Kai and K. Sakai.

Remarks. Counts and measurements of the hybrid specimens are shown in Tables 2 and 3 respectively. On the basis of genetic and morphological analyses, FAKU 85922 and 86957, and NMCI–P. 1527 were shown by Kai et al. (2011) to be hybrids of S. pachycephalus and S. nudus . FAKU 85922 had minute scales below the entire dorsalfin spine base and dark spots the prepelvic region. Accordingly, Kai et al. (2011) initially identified the specimen as S. p. pachycephalus sensu Matsubara (1943) (= S. pachycephalus here). Similarly, FAKU 86957 and NMCI–P. 1527 had minute scales below the entire dorsal-fin spine base but lacked dark spots on the prepelvic region, and Kai et al. (2011) initially identified them as S. p. nigricans sensu Matsubara (1943) (= S. pachycephalus here). However, a principal co-ordinate analysis using genetic data indicated that all three specimens occupied intermediate positions between the two species. A principal component analysis based on morphometric characters also indicated that they occupied equivocal positions in Kai et al. (2011). Accordingly, they were judged to be hybrids (Kai et al. 2011).

Although no genetic data was available for FAKU 6319 and FAKU 41980, both specimens had minute scales below the entire dorsal-fin spine base, pale markings on the dorsum (preserved condition), and no dark spots on the dorsal, anal, and caudal fins, i.e. a combination of diagnostic characters of both S. pachycephalus and S. nudus . Accordingly, they were regarded as putative hybrid specimens of the two species.

For the principal component analysis (PCA) for the characterization of hybrid specimens, 24 morphometric characters were selected on the basis of having complete data sets for each specimen. Incomplete data sets resulted in the following characters not being considered: body depth, pectoral fin length, pelvic fin length, and longest dorsal-fin ray length. On this basis, data from 162 specimens was utilized. The first principal component accounted for 87.3% of variation, all loadings being positive; thus it was considered a size component. Principal components 2 and 3 were shape components, with both positive and negative loadings. Together, they accounted for an additional 16.5% of variation. These components were then visually assessed as dimensions of shape, thereby providing separation of S. pachycephalus and S. nudus ( Fig. 7 ). PC2 was heavily loaded on the length of the first and second dorsal-fin spines, PC3 being loaded on interorbital width and length of the third anal-fin spine. Four of the five putative hybrid specimens fell into an equivocal position between S. pachycephalus and S. nudus , the fifth specimen (FAKU 41980) falling within the area of S. nudus specimens ( Fig. 7 ). Although that specimen had diagnostic characters of both S. pachycephalus and S. nudus , the result of the PCA suggested it to be rather closer to S. nudus in morphometric characters.

Figures

FIGURE 7. Plots of scores of principal components 2 and 3 based on 24 body measurements of the Sebastes pachycephalus complex: S. pachycephalus (open circles), S. nudus (crossed bars), hybrids (closed squares).