Abstract
Coilia grayii is the anadromous form of anchovy that is distributed in the East and South China Seas. It is a common fish species in the estuarine area of the Pearl River. Nevertheless, freshwater populations appear upstream in the Pearl River, but the migratory pathway has been mostly impeded by dam construction. Behavioral differences and constrained habitat within tributaries are suspected of promoting genetic divergence in these populations. In this study, we investigated the migratory behavior and genetic divergence of six populations of C. grayii fragmented by dams based on the otolith strontium/calcium (Sr/Ca) ratio, mitochondrial DNA, and microsatellite genotyping. All populations were in freshwater with low Sr/Ca ratios, except the estuarine population (Humen population) hatched in brackish water. Reduced nucleotide diversity corresponding to distance was observed. Populations from distant hydrological regions exhibited a decline in genetic diversity and a significant difference with the remaining populations after fitting the isolation by distance model. Pairwise fixation indices confirmed these results and moderate and significant differentiation was found between Hengxian site and downstream sites. Furthermore, STRUCTURE analyses revealed that all separated populations exhibited an admixed phylogenetic pattern except for individuals from the Hengxian locality. The upstream sites showed significantly increased resistance to gene flow from the estuarine population because of isolation by the dam. The results of the neutrality test and Bayesian skyline plots demonstrated complex demography—individuals’ experienced historical expansion and partial upper-dam populations had recently undergone a colonization, forming a new genetic structure. Accordingly, this study demonstrates differences in the migration pattern and genetic differentiation of C. grayii as a consequence of demographic history and current processes (habitat fragmentation and colonization).
Highlights
Improved understanding of anadromous fish population dynamics requires identifying the ecologically different populations, the genetic structure, and a better knowledge of the life histories of individuals in coastal habitats [1,2]
The combination of otolith microchemistry and genetic analyses suggested anadromous Coilia grayii were observed in the estuarine population which migrated among chemically distinct environments
We demonstrated that habitat fragmentation and long geographic distance had a significant effect on the genetic diversity of the upstream populations
Summary
Improved understanding of anadromous fish population dynamics requires identifying the ecologically different populations, the genetic structure, and a better knowledge of the life histories of individuals in coastal habitats [1,2]. Several organisms even take residence in opposite environments within diverse life histories, potentially derive into subpopulations [4,5], and display population structures that are dependent on the physical limitations of the habitat and their dispersal capability [6], including many anadromous species of salmon [5,7], some species of sturgeon [8,9], Hilsa shad Tenualosa ilisha [10,11]. These has important ramifications for population connectivity, population persistence, and the potential management of fish stocks. Identifying behavioral polymorphisms and exploring their cause promotes an understanding of how creatures adapt to the brackish water habitat and provides valuable insights for discerning the evolutionary forces on genetic divergence
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