萼花臂尾轮虫的种群遗传结构及系统地理格局研究

Recently, spatial patterns and evolutionary processes of population genetic differentiation in zooplankton have been one of the highlights to which ecologists pay attention increasingly. Due to its cyclically parthenogenetic reproduction, patchy nature of habitats and lack of hybridization, rotifer offers a excellent model system to study population genetic structure in zooplankton. In this program, Brachionus calyciflorus, occurring in freshwater frequently, will be collected from 18 natural waters in China, each of which represents a distinct climatic condition and water parameter, and clonally cultured in the lab. With molecular biological method, the mitochondrial COI gene and nuclear ITS region of rotifers will be PCR-amplified and sequenced. To identify and delimit putative cryptic species by the criterion of reproduction isolation, cross-mating experiments will be conducted with lineages whose sequence divergences are significant. By using Molecular Phylogeny, Analysis of Molecular Variance and Nested Clade Analysis, we will estimate the phylogenic relationships among cryptic species and population genetic structure within cryptic species of B. calyciflorus, and then discuss their phylogeographic patterns, which will not only reveal the spatial patterns and evolutionary processes in genetic differentiation of rotifer populations, but also explore the effects and mechanisms of habitat conditions on phylogeographic patterns of rotifer. Successful implementation of this program will make substantial contributions to understanding the processes such as ecological adaptation, population differentiation and speciation in zooplankton.

近年来，浮游动物种群遗传分化的空间格局及其演化进程已成为生态学家关注的焦点之一。轮虫因其具有周期性孤雌生殖、栖息地片段化和缺乏种间杂交等特点，从而成为浮游动物种群遗传结构研究的理想模式动物。本项目拟以淡水中常见的萼花臂尾轮虫为对象，于我国主要地理区域中选择气候条件和水环境参数具有明显差异的18个代表性水体进行轮虫样品的采集和克隆培养，运用分子生物学方法对轮虫线粒体DNA COI基因和核DNA ITS区进行扩增和测序；针对序列差异明显的谱系开展交配实验，以生殖隔离为标准划分隐种；运用分子系统学、分子方差分析和巢式支系分析等方法，研究萼花臂尾轮虫隐种间系统发生关系和隐种内种群遗传结构，并探讨其系统地理格局，不仅能揭示我国轮虫种群遗传分化的空间格局及其演化进程，还可探讨栖息地环境对轮虫系统地理格局的影响及作用机理。本项目的成功实施对理解浮游动物的生态适应、种群分化和物种形成等进程具有重要意义。

轮虫是浮游动物中四大类群之一，具有周期性孤雌生殖、栖息地片段化和缺乏种间杂交等特点，是研究浮游动物系统地理学较为理想的模式动物。本项目以淡水中常见的萼花臂尾轮虫为研究对象，选择我国七个气候区域中18个代表性水体进行萼花臂尾轮虫的采集和克隆培养，运用分子生物学方法对轮虫线粒体COI基因序列和核ITS区进行测定和分析；运用分子系统学和分子方差分析研究了萼花臂尾轮虫种复合体的遗传多样性、分子系统发生关系和隐种内种群遗传结构，并通过交配实验验证了支系间隐种关系；基于巣式支系分析等方法，探讨了萼花臂尾轮虫种复合体的系统地理格局，并结合采样区域的水环境参数、气候条件和地质历史事件，探讨了环境因子和地史事件对轮虫系统地理格局的影响机制。结果表明，萼花臂尾轮虫种复合体具有较高的遗传多样性，单倍型间序列差异百分比高；萼花臂尾轮虫是由4-6个隐种组成的种复合体，隐种间同域共存现象普遍；基于COI基因序列推定的萼花臂尾轮虫隐种III以及基于ITS序列得到的隐种复合体在各地理种群间分化显著，各地理种群间的遗传分化随空间距离的增加而增大；此外，轮虫种复合体的分布和遗传多样性还受到了水温和年均温的影响。参照Templeton（2004）给出的检索表推测长距离拓殖并伴随后期的栖息地片段化、有限的基因流和长距离扩散是影响萼花臂尾轮虫种复合体及其隐种现有地理分布格局的主要因素。萼花臂尾轮虫种复合体的地理分布及系统地理格局与末次盛冰期之后的物种退缩及中国南方的残遗种避难所有关。此外，各轮虫隐种的拓殖和适应能力的差异是形成不同隐种在我国广泛分布和局域性分布并存的现有系统地理格局的原因之一。本项目的成功实施对我国浮游动物的种群遗传结构及系统地理学研究产生了积极影响，对理解浮游动物的生态适应、种群分化和物种形成等进程具有重要意义。