Evolutionary History and Conservation Genetics of Horseshoe Crabs in the Indo-West Pacific
Date Issued
2014
Date
2014
Author(s)
Yang, Ming-Che
Abstract
The Indo-West-Pacific region (IWP) hosts the highest marine biodiversity on earth. The concordance among different species can be used to deduct the common mechanism that forms the IWP marine biodiversity. The horseshoe crab is an ancient marine arthropod, which has a wide geographic distribution cross the IWP and a long evolutionary history and importance in costal ecosystem and economics. However, loss of habitats and population degradation urged the need to study genetic connectivity and population demography for conservation. In my PhD dissertation there are three aims to be addressed: (1) To apply with phylogeographic methods of three species of horseshoe crabs (Tachypleus tridentatus, T. gigas, and Carcinoscorpius rotundicauda) probing in the speciation mechanism of the colonization routes (Chapter 2). (2) To compare how the effect of paleoclimate and paleogeology change on historical demography between two species horseshoe crab, T. tridentatus in the northwestern Pacific and T. gigas in the Indo-Malay Archipelago (Chapter 3). (3) To transfer the pattern of the genetic connectivity into design of reserves network and other conservation actions for horseshoe crabs along East and northern South China Sea (Chapter 4).
Phylogenetic relationship of three species of horseshoe crabs was revealed by mitochondrial (mt) COI, and AT-rich region. Based on dating Asian horseshoe crabs and Atlantic horseshoe crab (Limulus polyphemus) by fossil and biogeographic records of common ancestor and genetic variation of COI sequence, there were deep divergence at 24.7 ~33.6 million year ago (mya) between C. rotundicauda and two Tachypleus species, and 20.3~ 27.6 mya between T. gigas and T. tridentatus. The phylogenetic trees constructed by each marker all exhibited that only T. tridentatus had shallow genealogy relative to T. gigas. The deep divergent phylogeny of might be due to more isolation created by complicated sea basins and plate tectonic in Indo-Malay Archipelago than northwestern Pacific and also indicated the southern origin of Asian horseshoe crab according to the basal lineage in Indian Ocean. Pairwise difference (FST) also indicated that there was a significant differentiation between Indian and Pacific T. gigas populations.
Genetic variation of mt AT-rich region was examined for genetic connectivity and demography of 114 T. tridentatus individuals from Mainland China coast and Taiwan Strait, and 296 individuals from Japan coast. There was gradual growth in effective population size of horseshoe crab in Mainland China and Taiwan Strait after Last Glacial Maxima during the past 35 thousands years ago by using Bayesian Skyline plot, while horseshoe crabs began to colonize after last minor glacial period to Japan (3500~4500 years ago). The extremely low of genetic diversity in most Japan populations could result from loss of genetic connectivity measured by FST from other populations in the northwestern Pacific.
Based on genetic connectivity and historical demography in different spatial scale, it improve the measurement of the dispersal capacity of marine organism and realizing the risk and gain the information of conservation actions for those marine organism with lower dispersal capacity like horseshoe crab could sensitive to surfer from habitat degradation. A greater understanding of genetic connectivity could be used to realize the dispersal pattern and apply for reserve network design of T. tridentatus in East China Sea and north South China Sea. This dissertation also provides a conservation awareness to build a baseline for marine organisms, which are especially facing habitat deconstruction in the northwestern Pacific.
Subjects
鱟
印度西太平洋
演化史
地理親緣
保育遺傳
海洋保護區網絡
Type
thesis
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