Investigation of the hydrogeographical evolution of southwest China based on freshwater crab biogeography

在多变的环境中，不同流域之间的异源性可以被认为是水生生物多样化的主要驱动因素。虽然通过在陆地上的分散，排水系统之间的分离可能是一个积极的过程，但在许多情况下，河流系统的重新排列使种群孤立，并导致随后的物种形成。本项目研究了中国西南地区各种原生淡水蟹的历史生物地理学。它们居住在一个高度动态的景观中，在过去的1000万年里，由于青藏高原隆升过程中的排水重新安排，经历了重大的地理变化。在地球科学中，确定这些排水重新排列的年代仍然是一项困难的工作，尽管这些信息对理解景观演化至关重要，并有助于估计抬升速率。鉴于这些地理变化通常与物种形成有关，这些事件很可能反映在系统发育模式上。我打算根据一个有年代记录的淡水蟹系统发育来推断中国西南地区（四川、重庆）排水系统重新排列的时间。(1)我要问的是，四川盆地的淡水蟹是否是(a)从南部通过云南，和/或(b)从东部通过长江下游。在第一种情况下，淡水蟹的定殖很可能与长江上游的最终捕获有关，在后一种情况下，淡水蟹很可能随着长江中游支流的连续捕获而向上游扩散，或者分别是长江中游的逆转。(2)通过对淡水蟹类系统发育的时间校正，试图回答中扬子倒转是发生在青藏高原及其邻近地区初始上升时期的一个古老的中新世事件，还是不早于上新世。该项目将被纳入由中国科学院成都生物研究所牵头的一个更大的联合研究项目中，该项目旨在研究中国西南地区水生生物的进化和排水系统的发展。

In fluviatile environments, allopatry between drainages can be considered as a major driver of diversification in aquatic organisms. While separation between drainages can be an active process via dispersal over land, in many cases the rearrangement of river systems isolated populations and caused subsequent speciation.This project deals with the historical biogeography of the diverse primary freshwater crabs of Southwest China (family Potamidae). These inhabit a highly dynamic landscape that experienced major geographical changes during the last ten million years due to drainage rearrangements in the course of the uplift of the Tibetan plateau. Dating of these drainage re-arrangements remains a difficult endeavour in geosciences, even though this information is crucial to understand landscape evolution and can help to estimate uplift rates. Given that these geographical changes are often associated with speciation, these events are likely to be reflected by phylogenetic patterns. I intend to extrapolate the timing of drainage rearrangements in Southwest China (Sichuan, Chongqing) based on a dated freshwater crab phylogeny.(1) I ask wether colonization of the Sichuan basin with potamid freshwater crabs occurred (a) via Yunnan from the south, and/or (b) via the lower Yangtze from the east. In the first case colonization most likely correlates with the final capture of the upper Yangtze, in the latter case freshwater crabs most likely spread upstream with the successive captures of the middle Yangtze tributaries, or reversal of the middle Yangtze, respectively.(2) Based on time-calibrated phylogeny of the freshwater crabs I try to answer if reversal of the middle Yangtze is an old, Miocene event that occurred during initial rise of the Tibetan plateau and adjacent areas, or if it is not older than Pliocene.This project will be embedded in a larger joint research project lead by the Chengdu Institute of Biology, Chinese Academy of Sciences, targeting evolution of aquatic organisms and drainage development in Southwest China.