高原湖泊特有腹足类的种群衰退成因及其基本生物学研究

The highly endemic diversity of gastropods in the Yun-Gui plateau lakes is unique to China for its biotic resource, with some of them being important in economic value. This endemic biodiversity has suffered severely from strong anthropogenic intervention and has decreased dramatically in recent decades, but how to protect these native species is a tremendous challenge for conservationists and stakeholders. Herein, we aim to address this issue by choosing such a gastropod (Margarya melanioides) with highly economic value as one-case study. Based on the in-deep understanding of investigating its basic biology, population ecology and genetics, we try to propose the potential evidences to its population decline. Thus, the main interestings are first focused on: 1) its population size and geographic range, size-specific structure and composition; 2) its life history, strategies of development and reproduction and energy allocation; and 3) genetic diversity and structure of mitochondrial gene. Then, we will probe its possible extrinsic driving forces by analysing the relationship between its abundance of population and age-specific and measured environmental factors by using relative statistic models. And we also detect the likely intrinsic mechanisms of its reduction through collectively exploring the size-specific structure and composition, the intrinsic parameters and the variation of genetic structure. Finally, we integrate these two forces (outer and inner) into a proposed framework to qualify and quantify the key processes and mechanisms to the population shrink of M. melanioides. We expect that our results should provide useful information for planning efficient conservation strategies for M. melanioides. More expection is that it could provide a wide-use and appropriate framework and reference for rehabilitation and protection of the other extant endemic gastropods in the plateau lakes. Furthermore, our study should offer useful data for studing the systmetics and biogeography of the genus Margarya associated with its species diversification and evolution which remain unclear up to now.

云贵高原湖泊孕育了丰富的特有腹足类，它们是我国特有的生物资源，其中的许多物种还具有重要的经济价值。近年来人类活动的干预导致这些腹足类多为濒危物种，而如何恢复和保护它们是一个严峻的挑战。拟立项目以其中的一种经济腹足类-螺蛳为研究案例，在深入研究其基本生物学、种群生态学和分子生物学的基础上，探讨螺蛳种群衰退的关键驱动力。具体为：1)种群大小与地理分布、年龄结构与组成及个体特征；2)种群生活史特征、生长和生殖策略及能量分配；3)线粒体基因的遗传多样性。通过其种群数量与环境参数关系的解析，探究螺蛳衰退的关键外在驱动力；分析种群的年龄结构、生长及繁殖策略及其遗传结构差异，探讨其退化的内在机制。研究结果为构建有效的螺蛳保护策略提供科学依据，为探究如何有效恢复和保护其它现存的特有腹足类提供技术路线和理论框架，为螺蛳属的系统发育、物种分化格局以及其生物地理学研究等积累科学数据。

以特有种螺蛳为研究案例，在深入研究其种群生态学、基本生物学和遗传多样性的基础上，探究其种群衰退的关键驱动力，为构建有效的保护策略提供科学依据。研究结果如下：1）在近50年间，该物种经历了明显的衰退和分布地域的退缩。分布范围也由原本8个高原湖泊退缩至目前的2个：藻型湖泊滇池和草型湖泊海西海。其在滇池的平均密度由1940s的36 ind./m2降低至目前的0.036 ind./m2，且主要分布于东北部。海西海螺蛳的平均密度为0.111 ind./m2，显著高于其在的滇池的密度。从年龄结构上来看，滇池种群呈现老龄化现象，而海西海种群处于增长期与稳定期之间，年龄结构较滇池种群健康。分析显示，环境恶化是影响滇池螺蛳种群结构空间分布的重要因素，而底泥总磷、底泥pH、氧化还原容量和溶解氧是关键驱动力。2）分析了螺蛳生活史对策并估算了其周年次级生产量。螺蛳的理论体长为74.5 mm，理论寿命3.37年, 生长系数0.89，生长速度和生长加速度随年龄增大而趋近于零。该种雌雄异体，周年繁殖, 首次性成熟时间为158.4天(含胚胎发育50.4天)。互相关和非线性回归分析表明温度和壳长是影响其繁殖的重要外/内部因素。雌雄性比由1945的1.6:1降低至目前的1.05:1，繁殖力由3-7(1979年, 幼螺产量)和4个/只/月(2005年，胚胎数)降低至目前的1.79和2.45个/只/月。能量学研究表明，螺蛳次级生产量明显低于滇池的其它底栖动物种群，说明螺蛳获取资源较少，可能难以维持种群的发展。同时，螺蛳不同年龄的能量分配格局限制了螺蛳种群的繁殖力，这部分解释了螺蛳种群衰退的原因。因此，螺蛳的低繁殖力、性成熟晚和种群性比的紊乱和能量分配格局等是螺蛳种群衰退的重要内因。3）遗传多样性的分析显示，螺蛳种群的遗传多样性水平较高，滇池的三个群体在单倍型数(H)、单倍型多样性(Hd)、核苷酸多样性（Pi）和多态位点等遗传参数上均高于海西海群体。虽然各群体间存在一定的遗传分化，但也存在一定的基因交流。螺蛳种群的这种遗传特征是有利于螺蛳种群在自然界中的延续。

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