PRF/J: Mechanisms of Speciation in an African Rift Lake and the Relationship Between Morphological Divergence and Molecular Variation

我们将利用四个同源腹足类属的线粒体DNA序列来研究爆炸性物种形成对分子变异的影响。这解决了目前关于分支发生是否会增加分子进化速度的争议。根据这一数据，将使用系统发展图(待构建)来检验关于异地物种形成的两个相互竞争的假说；提出这些假说是为了解释东非坦噶尼喀湖特有动物的极端多样性。一种假说依赖于将湖泊分成不同的盆地，而另一种假说则认为现有的栖息地差异足以推动物种形成。一个高度多样化的地方性支系的两个基因的序列差异，它的非多样性姐妹群，一个相关的同域属，和一个河流外群。结果将显示：(A)形态和分子分歧如何与分支的相对年龄相关，以及(B)形态和分子分歧是否在不同的分支中相关。另一个目标是比较不同腹足类分支的线粒体序列变异模式与不同共域的慈鱼的线粒体序列变异模式，以得出一个一般的湖泊物种形成模式，并确定保护优先事项。将获得的分子数据集将用于检验以前对贝壳、软解剖和电泳学特征进行的形态计量学研究得出的系统发育结论。这些软体动物在物种数量、生活史和生态学方面并不是特别熟悉，因此这项研究将提供了解基础生物学细节的机会。过去对坦噶尼喀湖的研究主要集中在慈嘴鱼上，预期的研究将把它们放在更广泛的背景下，从而为这些调查提供一种比较的“标尺”。此外，这将是第一次对坦噶尼坎水生无脊椎动物进行分子遗传学研究，尽管它们是底栖生态系统的主要组成部分。

Mitochondrial DNA sequences from four prosobranch gastropod genera (Lavigeria, Limnotrochus, Reymondia, Cleopatra) will be used to examine the effect of explosive speciation on molecular variation. This addresses a current controversy over the question of whether cladogenesis increases the rate of molecular evolution. From this data a phylogeny (to be constructed) will be used to test two competing hypotheses of allopatric speciation; the hypotheses have been proposed to explain the extreme diversity of endemic fauna in Lake Tanganyika, East Africa. One hypothesis relies on separation of the lake into distinct basins while the other maintains that existing habitat differences are sufficient to drive speciation. Sequence divergence from two genes of a highly diverse endemic clade, its nondiverse sister group, a related sympatric genus, and a fluvial outgroup. Results will show: (a) how morphological and molecular divergence are correlated with relative ages of the clades, and (b) whether morphological and molecular divergence are correlated within the diverse clade. Another goal is to compare patterns of mitochondrial sequence variation in the diverse gastropod clade with those from a diverse sympatric cichlid fish to derive a general lacustrine speciation model and to identify conservation priorities. %%% The molecular data set to be obtained will be used to test phylogenetic conclusions that emerged from previous morphometric studies of shell, soft anatomy, and electrophoretic characters. These molluscs are not particularly well known with regard to number of species, life histories, and ecology, so this study will provide the opportunity to learn details of fundamental biology. Past studies of Lake Tanganyika focussed on cichlid fish and the intended studies promise to yield a sort of comparative "yardstick" for those investigations by placing them in a broader context. In addition this will be the first molecular genetic study of Tanganyikan aquatic invertebrates, despite the fact they are major components of the benthic ecosystem.