Abstract
Rhinogobius gigas is an amphidromous fish endemic to eastern Taiwan. Fishes with the diadromous behavior are expected to have a broader distribution range and higher genetic homogeneity despite that some amphidromous fishes with limited distribution are observed and R. gigas is an additional exception with a limited distribution range. Rhinogobius gigas has been documented to be retained inshore near the river plume with a short pelagic larval duration of 30–40 days, which may account for the endemism of this species. The short marine larval stage of R. gigas may imply a population genetic structure and the aim of the present study is to test whether the population genetic structure is present in R. gigas. To test the population genetic structure, fragments of mitochondrial displacement loop and cytochrome c oxidase subunit I were sequenced to provide molecular inference for genetic structure among populations. Sixty-nine haplotypes were identified among 191 R. gigas from 10 populations of eastern Taiwan and the mean haplotype and nucleotide diversities for all samples were 0.956 and 0.0024, respectively, implying a bottleneck followed by a recent population expansion further supported by Fu’s Fs (-26.6; p < 0.001) and Tajima’s D (-1.5; p = 0.037) values. The phylogenetic analysis revealed lack of genetic structure and the bush-like median joining network without commonly shared haplotypes supports the same scenario. The genetic homogeneity is probably due to the amphidromous life history providing the opportunity for passive larval transportation among the rivers through coastal currents in eastern Taiwan. The endemism to eastern Taiwan may be a consequence of complicated interactions among short pelagic larval duration, interspecific competition and coastal currents.
Highlights
Amphidromy is a life history of diadromous organisms, in which adults inhabit fresh water and their pelagic eggs or larvae drifting into estuaries or open oceans before settling down [1]
No ethical approval was required for this study because R. gigas was not an endangered species protected by the Wildlife Conservation Act in Taiwan and no experiment was conducted on live individuals
A 1,074-bp concatenated sequence of mtDNA c oxidase subunit I (COI) (554 bps) and D-loop (520 bps) was analyzed for 191 individuals obtained from 10 sampling sites (Fig 1) in rivers of eastern Taiwan
Summary
Amphidromy is a life history of diadromous organisms, in which adults inhabit fresh water and their pelagic eggs or larvae drifting into estuaries or open oceans before settling down [1]. Most amphidromous fishes are found in the tropical and subtropical areas and their planktonic larvae are considered to facilitate distant dispersals and population connections [2]. 80 days and show no genetic structure across their distribution range of Vanuatu, New Caledonia, and the Hawaiian Islands, respectively, while S. lagocephalus has PLD of c. 130–260 days and is distributed across the Indo-West Pacific deep genetic divergence was observed between oceanic basins [3,4,5]. More and more studies focusing on amphidromous fishes showed that the PLD is not always a key factor in shaping the distribution range and population structure. 40 days, Kuhlia rupestris can colonize remote islands and extend its range throughout the Indo-West Pacific at an evolutionary timescale the speciation may be ongoing [9,10]. In the light of the variety and complexity of amphidromous life history, case studies are important and could provide us better understandings of the population connection and evolution history of the mysteriously amphidromous fishes
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