DISSERTATION RESEARCH: Integrating Fossils and Molecules to Trace Ecological Divergence and Convergence in Marine Bivalves

亲缘关系密切的生物物种被认为会将彼此排除在特定的栖息地之外，因为它们会竞争相似的食物和栖息地资源。然而，许多密切相关的物种生活在同一地理空间。本研究剖析了近缘共生物种利用不同资源的生态压力与近缘共生物种扮演相似生态角色的进化趋势之间的张力。通过研究化石记录中成对亲缘物种的重要生态学特征，研究人员将研究每个物种的生态学，当它首先与它的近亲分离，然后与它们共同发生时，为这些物种相互作用时进化分歧或趋同的本质提供一个直接的窗口。因此，使物种在形态上更接近（当它们进入相同的环境时）和使它们分离（当它们进入生态竞争时）的压力平衡可以直接评估。这项研究将与正在进行的双壳类生命之树工作的成员合作，并提供密切相关的双壳类物种间生态进化的第一个例子之一。最后，该项目将培养一名研究生，并为研究人员提供课程材料。在芝加哥科学与工业博物馆为中学生举办的关于生态在进化中的作用的互动科学咖啡吧。研究人员将调查两个突出的生态学假说，这两个假说认为共生的、密切相关的物种应该在其生态特征上有所不同，以缓解对资源的直接竞争。？角色位移?预测物种共存后的竞争导致了它们的生态分化，而？物种分类?包括在形成共生关系之前在生态上已经不同的物种的共存。利用化石记录来追踪从异源性到同源性的转变，以及任何相应的生态性状随时间的变化，将在成对的相关物种中追踪特征位移和物种分选。本项目将构建美国沿海海洋双壳类Chione的分子系统发育（通过特征矩阵分析将9个现存物种和3个灭绝物种纳入分子树），结合空间明确的化石数据，将为特征位移、物种分类和系统发育相关性之间的关系提供独特的途径。考虑到生态相似性与亲缘关系相关的趋势，研究人员预计性状位移和物种分选将沿着一个连续体运行，其中性状位移在亲缘关系较近的物种之间占主导地位，而物种分选在亲缘关系较远的物种之间占主导地位。然而，环境强加的生态选择可能胜过竞争介导的选择。在这种情况下，物种将在它们共同出现的地方表现出相似的生态特征。

Closely related biological species are thought to exclude one another from a particular habitat because they compete for similar food and habitat resources. Yet, many closely related species inhabit the same geographic space. This research dissects the tension between 1) the ecological pressure on closely related, co-occurring species to use different resources, and 2) the evolutionary tendency for closely related species to play similar ecological roles. By studying ecologically important traits in pairs of closely related species in the fossil record, the researchers will study the ecology of each species when it is, first, isolated from, and then co-occurs with its near relative, giving a direct window into the nature of evolutionary divergence or convergence of those species as they interact. Thus, the balance of pressures pushing species closer in form (as they enter the same environment) and pushing them apart (as they come into ecological competition) can be assessed directly. This research will collaborate with members of the ongoing Bivalve Tree of Life effort and give one of the first examples of ecological evolution over time among closely related bivalve species. Finally, this project will train one graduate student and contribute course material to the researchers? interactive Science Café on the role of ecology in evolution for middle school students at the Chicago Museum of Science and Industry.The researchers will investigate two prominent ecological hypotheses that suggest co-occurring, closely related species should differ in their ecological traits to ease direct competition for resources. ?Character displacement? predicts that competition between species after they co-occur drives their ecological divergence whereas ?species sorting? involves the co-occurrence of species that already differed ecologically before coming into sympatry. Character displacement and species sorting will be tracked in pairs of related species by using the fossil record to trace shifts from allopatry to sympatry and any corresponding change in ecological traits through time. This project will construct a molecular phylogeny for a genus of marine bivalves along the American coasts, Chione (9 extant species plus 3 extinct species fitted into the molecular tree via analysis of character matrices), which coupled with spatially explicit fossil data will provide unique access to the relation between character displacement, species sorting, and phylogenetic relatedness. Given the tendency for ecological similarity to correlate with relatedness, the researchers expect character displacement and species sorting to operate along a continuum, where character displacement predominates between more closely related species and species sorting predominates between more distantly related species. However, ecological selection imposed by the environment may trump selection mediated by competition. In that case, species will express similar ecological traits where they co-occur.