Contrasting population genetic structures of congeneric coastal flounders associated with different early life...

Marine fish species are likely to exhibit little genetic differentiation among populations due to their high dispersal potential during early life stages and migratory nature. However, recent studies have increasingly reported intraspecific genetic differentiation resulting from species-specific ecological traits, environmental factors, and paleogeographic changes associated with glacial-interglacial cycles. Egg traits are considered to affect the level of genetic differentiation among populations; however, little is known about the specific differences in population genetic structure that result from variations in egg traits between closely related species. Using mitochondrial DNA sequences from the NADH dehydrogenase subunit 2 and cytochrome b genes, we compared population genetic structures of two congeneric coastal flounders around the Japanese Archipelago, yellow striped flounder Pseudopleuronectes herzensteini and marbled flounder P. yokohamae, which exhibit contrasting early life-history traits related to dispersal, including egg traits. No genetic differentiation was observed among sampling locations of P. herzensteini (global F_ST = -0.002), which spawns pelagic eggs and has a longer planktonic larval duration than P. yokohamae. Historical demographic analyses suggest that P. herzensteini has maintained a large population size over time, with extensive gene flow across the sampling area. In contrast, six genetic groups were identified in the adhesive demersal egg spawner P. yokohamae, with some genetic barriers to gene flow among them (global F_ST = 0.171). Distinctive population demographic histories were inferred for each group, suggesting that paleogeographic changes during the Late Pleistocene greatly influenced the local population formation. These findings indicate that the highly sedentary characteristics in early life stages of P. yokohamae lead to greater population divergence and distinct demographic histories. Such findings also provide important insights into the development of sustainable fisheries management for both species.