ddRAD‐Seq reveals evolutionary insights into population differentiation and the cryptic phylogeography of Hyporhamphus intermedius in Mainland China

Abstract Species differentiation and local adaptation in heterogeneous environments have attracted much attention, although little is known about the mechanisms involved. Hyporhamphus intermedius is an anadromous, brackish‐water halfbeak that is widely distributed in coastal areas and hyperdiverse freshwater systems in China, making it an interesting model for research on phylogeography and local adaptation. Here, 156 individuals were sampled at eight sites from heterogeneous aquatic habitats to examine environmental and genetic contributions to phenotypic divergence. Using double‐digest restriction‐site‐associated DNA sequencing (ddRAD‐Seq) in the specimens from the different watersheds, 5498 single nucleotide polymorphisms (SNPs) were found among populations, with obvious population differentiation. We find that present‐day Mainland China populations are structured into distinct genetic clusters stretching from southern and northern ancestries, mirroring geography. Following a transplant event in Plateau Lakes, there were virtually no variations of genetic diversity occurred in two populations, despite the fact two main splits were unveiled in the demographic history. Additionally, dorsal, and anal fin traits varied widely between the southern group and the others, which highlighted previously unrecognized lineages. We then explore genotype–phenotype‐environment associations and predict candidate loci. Subgroup ranges appeared to correspond to geographic regions with heterogeneous hydrological factors, indicating that these features are likely important drivers of diversification. Accordingly, we conclude that genetic and phenotypic polymorphism and a moderate amount of genetic differentiation occurred, which might be ascribed to population subdivision, and the impact of abiotic factors

Growth, osmoregulatory and hypothalamic–pituitary–somatotropic (HPS) axis response of the juvenile largemouth bass (Micropterus salmoides), reared under different salinities

A 40 day experiment was conducted to investigate the effects of different salinities (0, 5 and 10 ppt) on the growth, osmoregulatory and hypothalamic–pituitary–somatotropic (HPS) axis response of juvenile largemouth bass (Micropterus salmoides). At the same time, two extra groups salinities (8 and 9 ppt) were used to explore the threshold of osmoregulation in M. salmoides to salinity stress. The survival were 94.45 %, 98.15 % and 32.00 % in 0, 5, 10 ppt, respectively. According the final body weight, specific growth rate (SGR), feed conversion ratio (FCR), condition factor (K) and chemical composition of muscle, largemouth bass should not be cultured at or above 10 ppt and 5 ppt is better than 0 ppt. The results found that the content of serum prolactin (PRL) and cortisol (COR) were no significant differences between groups of the 0, 5, 8, 9 and 10 ppt. Compared with the control group (0 ppt), the serum thyroxine (T4) content of 8 and 9 ppt groups decreased significantly and the serum triiodothyronine (T3) content all decreased significantly. Serum osmolality increased with increasing salinity. Na+-K+-ATP (NKA) and Ca2+-Mg2+-ATP (CMA) activities in the gills of largemouth bass at 0, 5, 8, 9 and 10 ppt showed tendency of ascend at first and descend at last, among which the activities in 10 ppt were significantly lowest. Gene expression of hepatic growth hormone (GH) at 10 ppt was highest. Meanwhile, insulin-like growth factor-I (IGF-I) expression at salinities of 8, 9 and 10 ppt were significantly higher than those at 0 and 5 ppt. Taken together, the findings of this study provide guidance for the practical rearing of largemouth bass in saline waters and contribute to research on stress physiology