Phylogeography, Demographic History, and Reserves Network of Horseshoe Crab, Tachypleus tridentatus, in the South and East China Seaboards

Molecular genetic data can be used to diagnose the status of populations and provide the management information. The loss of habitats and population degradation of the tri-spine horseshoe crab, Tachypleus tridentatus, in Asia urged the need to study patterns of phylogeography and population demography for its conservation. In this Study, we first reviewed the marine reserves for T. tridentatus in the South and East China Seaboards, and genetic variation of mitochondrial (nit) AT-rich region was then examined for 114 T. tridentatus individuals. They were collected from eight populations in the northern South China Sea and East China Sea, including Zhoushan (ZS), Yangjing (YH), Beihai (BB), and Kinmen (TK) along the southeast coast of Mainland China, Penghu Island, Tiexiawei (TT), and Dongwei (TD) and in the Taiwan Strait, and Budai (TB) and northern coast in Taiwan (TN). Pairwise tests of genetic differentiation (F-ST) indicated two populations, Budai and Tiexianwei, were significantly different from others. The genetic connectivity of the other six Populations showed a pattern consistent with an isolation-by-distance model of gene flow. Mismatch distribution analyses indicated that three populations, Beihai, Yangjing, and Zhoushan, had a pattern consistent with range expansion and three populations appeared to be in equilibrium (northern Taiwan, Kinmen, and Dongwei). Budai and Tiexianwei, located in semi-enclosed embayments had patterns of nucleotide substitution consistent with recent population bottlenecks. Those populations that appear to have undergone recent range expansion are all along the Mainland China coast and Could have been affected by glacial sea-level fluctuations along the northern South and East China Seaboard. Populations estimated to have undergone a bottleneck may have had reduced gene flow due to geographic barrier that contributed to inbreeding depression based on evidence of lower genetic diversity. Finally, a greater understanding of genetic connectivity could be used to realize the dispersal pattern and apply for reserve network design of horseshoe crab.