Rhamphocottus nagaakii (Cottoidea: Rhamphocottidae), a new species of grunt sculpin from the northwestern Pacific, with notes on the phylogeography of the genus Rhamphocottus

• Published in: Ichthyological research 2023-04, Vol.70 (2), p.268-285
• Main Authors: Munehara, Hiroyuki, Togashi, Kouji, Yamada, Sayuri, Higashimura, Takushi, Yamazaki, Aya, Suzuki, Shota, Abe, Takuzo, Awata, Satoshi, Koya, Yasunori, Tsuruoka, Osamu
• Format: Article
• Language: English
• Subjects: Animal morphology; Animal Systematics/Taxonomy/Biogeography; Archipelagoes; Biomedical and Life Sciences; Ecology; Freshwater & Marine Ecology; Life Sciences; Miocene; Morphometry; New species; Pliocene; Rhamphocottus; Rhamphocottus richardsonii; Speciation; Zoology
• ISSN: 1341-8998; 1616-3915
• DOI: 10.1007/s10228-022-00885-y

A new species of grunt sculpin, Rhamphocottus nagaakii inhabiting the northwestern Pacific, previously identified as Rhamphocottus richardsonii Günther 1874, is described based on genetic evidence and morphological differences. The new species can be distinguished based on morphometric characters related to the head, including head length [45.3–54.6% of standard length (SL)], postorbital head length (18.8–25.5% SL) and the length of pectoral-fin base (15.8–20.7% SL), which are smaller than in R. richardsonii (53.6–60.5% SL, 26.2–31.7% SL, and 19.5–25.2% SL, respectively). Genetic differences between two species markedly exceed levels for intra-specific differences. Rhamphocottus nagaakii is considered to have arisen from a common ancestor of the two species, which probably inhabited somewhere the North Pacific Rim around the Aleutian Archipelago. During a period of cooling in the Pliocene or the Miocene, R. nagaakii and R. richardsonii became separated to the southern regions of the northwestern and northeastern Pacific, and subsequently underwent speciation.