US-Tanzania Dissertation Enhancement: Diversification in Lake Tanganyika Endemics: Gastropods and Cichlid Fishes Compared

自从他们被发现以来，东非裂谷湖泊的慈鱼动物群作为湖内物种形成和适应性分化的显著案例而引起了人们的注意。然而，在这些湖泊中，坦噶尼喀湖的独特之处在于，它的其他类群也出现了多样化：在这个湖中发现了350多种独特的非鱼纲动物。因此，坦噶尼喀湖是研究地方性多样性过程的独特生态系统：为什么一些类群在这个单一的湖泊内如此戏剧性地多样化？一种假设是，滨海地带的底物异质性使分类群在生态上专门针对特定的底物，而这种异质环境中的亚种群之间的隔离创造了物种形成的可能性。尽管这种关于湖内异地物种形成的假说最早是在25年前提出的，但它在东非裂谷湖泊内创造物种多样性格局方面的作用在很大程度上仍未得到检验。如果通过底物专一性和生境斑块之间有限的扩散来隔离种群推动了多样性，那么可以假设，来自具有高度特有多样性的种群的物种将显示出种群之间受限的基因流动的证据。这项研究将在坦噶尼喀湖产生大量地方性辐射的两个不相关的群体中调查这一假设：拉维格里亚腹足类动物和特洛菲尼部落的慈嘴鱼。研究种类的慈鱼和蜗牛都是局限于岩石基质的底栖草食动物。这种专有的栖息地联系，再加上它们在整个湖泊范围内显著较高的物种多样性，表明在岩石基质上的生态专门化促进了蜗牛和葫芦种群的物种形成。因此，生态专门化可能推动种群的并行遗传细分和在多个不相关的分类群中的多样化。为了验证这些假设，将使用线粒体DNA序列和微卫星数据来分析坦桑尼亚基戈马附近不同海岸线上的慈鱼和蜗牛种群遗传结构的比较模式。了解生态专业化对这些类群的基因流动动态和多样性模式的影响，将有助于测试关于坦噶尼喀湖异常多样化的动物群之间的多样化过程的重要的、长期存在的问题。

Since their discovery, the cichlid fish faunas of the East African rift lakes have drawn attention as remarkable cases of within-lake speciation and adaptive divergence. Among these lakes, however, Lake Tanganyika is distinctive in the extent to which its other taxa have also diversified: over 350 unique non-cichlid species are found within this lake. Tanganyika is therefore a unique ecosystem for studying processes of endemic diversification: how is it that some taxa have diversified so dramatically within this single lake? One hypothesis is that substrate heterogeneity in the littoral zone allows taxa to ecologically specialize on specific substrates, and isolation between subpopulations in this heterogeneous environment creates the potential for speciation. Although this hypothesis for within-lake allopatric speciation was first proposed over 25 years ago, its role in creating patterns of species diversity within the East African rift lakes remains largely untested. If isolation of populations through substrate specificity and limited dispersal among habitat patches has driven diversification, it is hypothesized that species from groups with high endemic diversity will show evidence of restricted gene flow between populations. This research will investigate this hypothesis in two unrelated groups that have produced substantial endemic radiations in Lake Tanganyika: Lavigeria gastropods, and cichlid fishes of the tribe Tropheini. Study species of cichlid fishes and snails are all benthic herbivores restricted to rocky substrates. This obligate habitat association, coupled with their notably high lake-wide species diversity, suggests that ecological specialization on rocky substrate has promoted speciation in both snail and cichlid groups. Therefore, ecological specialization may drive parallel genetic subdivision of populations and diversification in multiple unrelated taxonomic groups. To test these hypotheses, both mitochondrial DNA sequence and microsatellite data will be used to analyze comparative patterns of population genetic structuring in cichlids and snails along the heterogeneous shoreline bordering Kigoma, Tanzania. Understanding the impact that ecological specialization has on gene flow dynamics and patterns of diversity across these taxa will allow the testing of important, long-standing questions about the processes of diversification among Lake Tanganyika's exceptionally diverse faunas.