Genetic and phenotypic differentiation among Galaxias maculatus populations in a Patagonian postglacial lake system

Understanding the influence of landscape features on population differentiation is fundamental to evolutionary biology studies. We examined spatial patterns of genetic and phenotypic variability among Galaxias maculatus populations in a complex of four postglacial lakes in northwestern Patagonia differing in size and connectivity among them. A hierarchical Bayesian analysis grouped the individuals collected from 11 localities into 3 genetic clusters, first defining the populations of the two large lakes and separating the two small lakes in subsequent analysis. Genetic structuring was restricted within large lakes. It is known that the larval stage of Galaxias maculatus migrate to the limnetic zone of Patagonian lakes, possibly exerting an homogenizing effect on gene flow within lakes. Gene flow asymmetry and divergences among lakes can be explained by a combination of landscape characteristics and the presence of predators in the short streams that connect them. Individuals from the small lakes are the most divergent morphologically and genetically. The population in the isolated Redonda Lake, exhibit meristic differences as well, suggesting strong drift and environmental effects. This population is likely to have been isolated following the decline in water level of a paleolake that existed in this region approximately 13.2 kya BP.

解析景观特征对种群分化的调控作用，是进化生物学研究的核心基础课题。本研究以巴塔哥尼亚西北部4个面积与连通性均存在差异的冰后湖（postglacial lakes）群中的斑纹南乳鱼（Galaxias maculatus）种群为研究对象，探讨其遗传与表型变异的空间分布格局。通过分层贝叶斯（hierarchical Bayesian）分析，我们将11个采样点采集的个体划分为3个遗传簇：首次聚类即区分出两个大型湖泊的种群，后续分析进一步分离出两个小型湖泊的种群。遗传结构分化仅局限于大型湖泊内部。已知斑纹南乳鱼的幼体阶段会迁移至巴塔哥尼亚湖泊的湖沼带（limnetic zone），该行为可能对湖泊内部的基因流产生均质化效应。湖泊间的基因流不对称性与种群分化程度，可通过景观特征与连接各湖的短小溪流中捕食者的存在情况联合解释。来自小型湖泊的个体在形态学与遗传学层面均表现出最高程度的分化。孤立的雷东达湖（Redonda Lake）种群同样表现出可数性状差异，这暗示存在强烈的遗传漂变与环境选择作用。该种群的孤立状态，大概率形成于该区域距今约13.2千年的古湖（paleolake）水位下降事件之后。