Genetic patterns reveal northward range expansion and cryptic diversity in Nalbant’s spined loach, Cobitis nalbanti sensu lato (Teleostei: Cypriniformes: Cobitidae)

Abstract

The morphologically similar populations of the Korean freshwater spined loach recently described as a new species Cobitis nalbanti (Actinopterygii: Cypriniformes: Cobitidae) inhabit the rivers and streams on the Korean Peninsula that flow into the Yellow Sea and the Korea Strait. These shallow sea areas have experienced recurrent sea-level rises and falls. In this study, we investigate the impact of repeated disconnection and reconnection of rivers on the population genetics and morphological variation of C. nalbanti. A total of 264 individuals of C. nalbanti were collected from 17 localities covering the entire distribution range of this species in South Korea. We examined multi-locus genetic data including a mitochondrial gene, seven nuclear genes and eight microsatellite loci, and scrutinized 31 morphological variables based on 26 morphometric and 3 meristic characters. We uncovered a population genetic structure and noticeable morphological variation among populations approximately corresponding to the geography of river basins along the Yellow Sea. Overall genetic diversity was significantly reduced in the more northern populations, suggesting range expansion from ancestral southern populations into northern rivers via the paleo-Yellow River system in the Yellow Sea during glacial periods of lowered sea levels. A northward range expansion hypothesis was strongly supported by the reconstruction of geographic ranges of ancestral species and/or populations based on phylogenetic analyses. Both mitochondrial and nuclear phylogenetic trees revealed a relatively highly divergent lineage of C. nalbanti in the southernmost populations (Tamjin lineage). Noticeable differences in morphological variables between the Tamjin lineage and other lineages of C. nalbanti also suggest potential separate specific status of the former. The close phylogenetic relationships between the Tamjin lineage and the Japanese species of Cobitis signify interaction or exchange between the Korean and Japanese cobitids and imply that there was historically at least one freshwater passage on the terrestrial bridge between the Korean Peninsula and the southwestern part of the Japanese archipelago.

Key words:

• Cobitidae
• dispersal
• morphology
• Pleistocene
• Pliocene
• phylogeny
• population genetic structure
• range expansion

Acknowledgements

The authors thank Jun Nakajima (Fukuoka Institute of Health and Environmental Sciences) for providing Japanese fish samples, and Elizabeth M.A. Kern and Hyung-Bae Jeon for careful reading and constructive comments on the early manuscript. One reviewer provided significant comments on the first version of the manuscript. We thank the reviewer.

Disclosure statement

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.

Supplemental data

Supplemental data for this article can be accessed here: http://dx.doi.org/10.1080/14772000.2020.1737842.

Associate Editor: Kevin Conway

Additional information

Funding

This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT and Future Planning (2013R1A1A2062008) to Yong-Jin Won and by the State Project АААА-А16-116021660077-3 to Ekaterina Vasil’eva.