EFFECTIVE POPULATION SIZE AND CONNECTIVITY IN FISH

在进化和保护生物学的一个基本问题是栖息地破碎化如何影响种群之间的遗传多样性分布和种群适应当地条件的能力。在我的研究中，我使用有效种群大小（Ne）作为衡量种群遗传多样性的指标，并研究了在复杂景观中发现的鱼类种群的Ne的确定机制。 有效种群大小通过与种群持续性和进化潜力的联系，对物种保护具有重要意义。 大多数物种都是通过不同程度的基因流动（元种群）相互连接的种群网络自然发生的。 因此，遗传多样性的模式是影响当地人口Ne的机制（随机损失，当地自适应选择，基因流）和元人口（元Ne）的有效规模的产物。基因流动往往会增加当地种群的Ne，通过抵消随机损失的遗传多样性，而定向选择可能会减少多样性。对于集合种群，理论预测，如果当地种群对下一代的贡献不均匀，则碎片化系统的集合Ne将小于类似大小的panmictic系统。然而，在复杂的、分层布置的树突环境中，预测的Meta Ne可以大于局部Ne的总和。例如，树枝状流域有一个当地人口的等级安排，通常会导致不对称的基因流。元Ne也可以受到景观中的环境变化，使种群受到不同的选择压力。 我的长期目标是阐明空间复杂的集合种群系统中鱼类局部适应的基因组基础，并确定基因流及其不对称性如何影响中性和适应性遗传多样性的模式。我将研究几个温带冰川后景观（新斯科舍省，纽芬兰，拉布拉多和巴塔哥尼亚）的系统，在破碎和连通性的水平对比。 这些树枝状的排水沟在大小和复杂性上不同，因此可能在不对称基因流和适应过程的相对重要性上不同。我还将比较模式的遗传多样性的同域物种的景观，包含湖泊与对比选择压力（水的pH值，透明度，生产力）非常不同的生活史特征。我们的目标将是解开基因流的影响，适应过程和物种的生活史上本地Ne的和元Ne。这项工作的一部分将发生在西部河片港排水在新斯科舍省，一个高度复杂的树枝状系统的近20个相互连接的湖泊不同的环境变量，并包含三个丰富的同域物种，不同的一些关键的生活史特征：带状鳉鱼，黄鲈鱼，和白色吸盘。我正在进行的研究，解决类似的和相关的问题，鲑鱼物种将继续专注于在纽芬兰的上游亨伯河系统，而在巴塔哥尼亚，我将研究模式的殖民化和适应盐度在广泛的Galaxias maculatus。在连通性光谱的另一端，我也研究海洋物种，包括大西洋鲱鱼，一种高度丰富和广泛的中上层鱼类。这一机构的研究将构成一些第一个实证检验的理论预测的影响，连接的本地人口Ne的和元Ne之间的关系，并应给我们一些想法的有用性的理论理解真实的系统，以及帮助指出进一步的理论发展的方向。

A fundamental question in evolutionary and conservation biology is how habitat fragmentation influences the distribution of genetic diversity among populations and the ability of populations to adapt to local conditions. In my research, I use effective population size (Ne) as a measure of the genetic diversity of populations, and examine the mechanisms that determine the Ne of populations of fish found in complex landscapes. Effective population size is of importance to species conservation through its links to population persistence and evolutionary potential. Most species occur naturally as networks of populations interconnected by varying degrees of gene flow (meta-populations). Patterns of genetic diversity are thus a product of mechanisms that influence local population Ne’s (stochastic loss, local adaptive selection, gene flow), and the effective size of the meta-population (meta-Ne). Gene flow tends to increase Ne of local populations by countering the stochastic loss of genetic diversity, while directional selection is likely to reduce diversity. For meta-populations, theory predicts that the meta-Ne of a fragmented system will be smaller than that of a similar-sized panmictic system, if local populations contribute unevenly to the next generation. In complex, hierarchically arranged dendritic environments, however, the predicted meta- Ne can be greater than the sum of the local Ne’s. Dendritic watersheds, for example, have a hierarchical arrangement of local populations that usually leads to asymmetrical gene flow. Meta-Ne can also be affected by the environmental variation in the landscape that subjects populations to different selective pressures. My long term goals are to elucidate the genomic basis of local adaptation in fish within spatially complex meta-population systems, and to determine how gene flow and its asymmetries affect patterns of neutral and adaptive genetic diversity. I will be examining systems in several temperate post-glacial landscapes (Nova Scotia, Newfoundland, Labrador and Patagonia) that contrast in level of fragmentation and connectivity. These dendritic drainages differ in size and complexity, and thus are likely to differ in the relative importance of asymmetric gene flow and adaptive processes. I will also compare patterns of genetic diversity for sympatric species with very different life history traits in landscapes that contain lakes with contrasting selection pressures (water pH, transparency, productivity). The goal will be to disentangle the effects of gene flow, adaptive processes and species life histories on local Ne’s and meta-Ne. Some of this work will take place in the West River Sheet Harbour drainage in Nova Scotia, a highly complex dendritic system of nearly 20 interconnected lakes differing in environmental variables and containing three abundant sympatric species that vary in some key life history traits: banded killifish, yellow perch, and white sucker. My ongoing research addressing similar and related questions in salmonid species will continue focusing on the upper Humber river system in Newfoundland, while in Patagonia I will examine patterns of colonization and adaptation to salinity in the widespread Galaxias maculatus. At the other end of the connectivity spectrum I also work with marine species, including Atlantic herring, a highly abundant and widespread pelagic fish. This body of research will constitute some of the first empirical tests of the theoretical predictions regarding the effects of connectivity on the relationship between local population Ne’s and meta-Ne, and should give us some idea of the usefulness of the theory for understanding real systems as well help to indicate directions for further theoretical development.