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

密切相关的生物物种被认为会在特定的栖息地中相互排斥，因为它们会争夺相似的食物和栖息地资源。然而，许多密切相关的物种居住在同一地理空间。本研究剖析了1）生态压力之间的紧张关系，密切相关的，共同发生的物种使用不同的资源，2）进化趋势密切相关的物种发挥类似的生态作用。通过研究化石记录中成对密切相关物种的生态学重要特征，研究人员将研究每个物种的生态学，当它首先与其近亲隔离，然后与其近亲共同出现时，为这些物种相互作用时的进化分歧或收敛的性质提供了一个直接的窗口。因此，推动物种在形式上更接近（当它们进入同一环境时）和推动它们分开（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，并在密切相关的双壳类物种中提供生态进化的第一个例子。最后，本计画将培养一位研究生，并提供课程教材给研究人员。在芝加哥科学与工业博物馆为中学生举办的关于生态学在进化中的作用的互动科学咖啡馆。研究人员将调查两个突出的生态学假设，这两个假设表明，共同出现的密切相关的物种应该在生态特征上有所不同，以减轻对资源的直接竞争。?角色置换？预测，物种之间的竞争后，他们共同出现驱动器的生态分歧，而？物种分类涉及到物种的共存，这些物种在进入同域性之前就已经在生态上不同了。通过使用化石记录来追踪从异地分布到同域分布的变化以及生态特征随时间的任何相应变化，将成对地追踪相关物种的特征位移和物种分类。该项目将为沿着美国海岸的一种海洋双壳类--Chione（9个现存物种和3个灭绝物种通过特征矩阵分析拟合到分子树中）构建一个分子系统发生学，该分子系统发生学与空间上明确的化石数据相结合，将为特征位移、物种分类和系统发生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，研究人员预计性格置换和物种分类将沿着一个连续体运作，其中性格置换在亲缘关系较近的物种之间占主导地位，而物种分类在亲缘关系较远的物种之间占主导地位。然而，由环境施加的生态选择可能胜过由竞争介导的选择。在这种情况下，物种将在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.