Age, growth, reproductive biology, color pattern, and ontogenetic divergence of two closely related rock?shes (Sebastes koreanus and S. nudus) off the coasts of the Shandong Peninsula, China

The live-bearing genus Sebastes is renowned for its outstanding species richness and color diversity,and its speciation has been a point of interest.This study investigated the age,growth,reproductive biology,color pattern and ontogenetic divergence of a pair of closely related rockfishes from the coasts of the Shandong Peninsula,namely,Sebastes koreanus(n=879)and S.nudus(n=257).Marginal increment analysis of sectioned otoliths showed that annulus formation occurred once a year between June and July in both species.The sex-pooled growth curves of S.nudus and 3 populations of S.koreanus differed significantly from each other.No apparent latitudinal cline in growth parameters was found in S.koreanus.For both species,the peak parturition periods were from April to May,and the peak copulation periods were from November to December.S.nudus has a highly variable and conspicuous color pattern while S.koreanus has a stable and dull color pattem.This difference,together with the overlapping distribution and the close relationship,make S.koreanus and S.nudus an ideal model to investigate the color-driven speciation of the Sebastes.We confirmed that S.nudus changes its body color with age and season and fully expresses the carotenoid-based nuptial coloration when the fish reaches first maturity.Moreover,our comparisons of morphological traits that are likely related to survival and quality of these fishes suggested that S.nudus may suffer higher predation risk and foraging difficulty beginning at age 3.In light of the ontogenetic development of the color pattern in S.nudus,we suggested that the full expression of nuptial coloration most likely triggers the strong selective pressure to enhance swimming performance,anti-predator defense and foraging capacity of S.nudus through predator-prey interactions.By understanding all these details,we further inferred a hypothesis that both color pattem and bathymetric segregation play key roles in facilitating the speciation of demersal rockfishes.

The live-bearing genus Sebastes is renowned for its outstanding species richness and color diversity, and its speciation has been a point of interest. This study investigated the age, growth, reproductive biology, color pattern and ontogenetic divergence of a pair of closely related rock?shes from the coasts of the Shandong Peninsula, namely, Sebastes koreanus( n =879) and S. nudus( n =257). Marginal increment analysis of sectioned otoliths showed that annulus formation occurred once a year between June and July in both species. The sex-pooled growth curves of S. nudus and 3 populations of S. koreanus dif fered signi?cantly from each other. No apparent latitudinal cline in growth parameters was found in S. koreanus. For both species, the peak parturition periods were from April to May, and the peak copulation periods were from November to December. S. nudus has a highly variable and conspicuous color pattern while S. koreanus has a stable and dull color pattern. This dif ference, together with the overlapping distribution and the close relationship, make S. koreanus and S. nudus an ideal model to investigate the color-driven speciation of the Sebastes. We con?rmed that S. nudus changes its body color with age and season and fully expresses the carotenoid-based nuptial coloration when the ?sh reaches ?rst maturity. Moreover, our comparisons of morphological traits that are likely related to survival and quality of these ?shes suggested that S. nudus may suf fer higher predation risk and foraging difficulty beginning at age 3. In light of the ontogenetic development of the color pattern in S. nudus, we suggested that the full expression of nuptial coloration most likely triggers the strong selective pressure to enhance swimming performance, anti-predator defense and foraging capacity of S. nudus through predator-prey interactions. By understanding all these details, we further inferred a hypothesis that both color pattern and bathymetric segregation play key roles in facilitating the speciation of demersal rock?shes.