Neogene Caribbean Biotic Turnover and Evolution of Geminate Mollusc Species Separated by the Isthmus of Panama

长期以来，中美洲地峡（CAI）的上升和连接热带东太平洋（EP）和西大西洋（WA）海洋的海道的逐渐关闭一直是理解海洋中新物种形成的模型。根据地质信息，海道关闭的最后阶段是在310万至350万年前，研究人员假设，今天在地峡两侧发现的数百对形态相似的物种（称为“双生”或双胞胎物种）被认为代表了在地峡形成之前广泛分布于热带东太平洋和西太平洋的单一祖先物种的后代。然而，最近的证据提出了一个问题，即CAI的关闭实际上是如何影响热带美洲物种多样性的模式的。考虑到地峡形成后一些种群的灭绝率可能高达70%，研究人员认为，在两个海洋中幸存下来的姐妹类群应该很罕见。这么多现存的双生殖物种在东太平洋和西太平洋的明显生存，怎么能与正在发展的加勒比生物大规模更替的古生物学图景相协调呢？为了回答这个问题，北卡罗来纳大学的彼得·马科博士将对双壳类软体动物阿基达科双生殖物种复合体的物种形成和灭绝进行分子和古生物相结合的分析。结合核和线粒体基因变异的系统地理调查以及形态特征的判别分析，将对现存物种进行区分。然后，化石记录中的物种区分将通过将对现存动物群中遗传上不同的物种之间形态差异的统计测试扩展到化石记录中的标本来完成。该研究将为两名研究生提供实地收集、形态计量学和分子系统发育方面的资金支持和培训，并资助学生参加全国会议，以获得展示研究成果的经验。基金还将为分子研究方面的本科教育和培训提供机会，PI将积极从传统上代表性不足的群体中招募个人。虽然没有直接由该提案资助，但分子系统发育工作也将与英国形态系统学家进行的系统发育工作相结合。

The rise of the Central American Isthmus (CAI) and the gradual closure of the seaway connecting the tropical Eastern Pacific (EP) and Western Atlantic (WA) oceans has long served as a model for understanding the formation of new species in the sea. Given geological information that dates the final stage of seaway closure at 3.1-3.5 million years ago, researchers have hypothesized that hundreds of morphologically similar pairs of species found today on either side of the isthmus (called "geminate" or twin species) are believed to represent the descendants of single ancestral species broadly distributed throughout the tropical EP and WA oceans prior to the isthmus formation. Recent evidence, however, raises questions about how closure of the CAI actually affected patterns of species diversity in tropical America. Given that extinction rates may have been as high as 70% for some groups following isthmus formation, researchers think that sister-taxa that survived in both oceans should be rare. How can the apparent survival of so many living geminate species in both the EP and WA be reconciled with the developing paleontological picture of massive Caribbean biotic turnover? To answer this question, Dr. Peter Marko of the University of North Carolina will conduct a combined molecular and paleontological analysis of speciation and extinction among geminate species complexes in the bivalve mollusk family Arcidae. Living species will be discriminated with a combination of phylogeographic surveys of nuclear and mitochondrial gene variation along with discriminant analysis of morphological traits. Species discrimination in the fossil record will then be accomplished by extending statistical tests of morphological differences among genetically distinct species in the living fauna to specimens from the fossil record. The research will provide financial support and training in field collections, morphometrics, and molecular phylogenetics for two graduate students plus funds to send students to a national meeting to gain experience presenting research results. Funds will also offer opportunities for undergraduate education and training in molecular research and the PI will actively recruit individuals from traditionally underrepresented groups. Although not directly funded by this proposal, the molecular phylogenetic work will also be integrated with a phylogenetic effort conducted by a morphological systematist in the UK.