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

中美洲地峡（CAI）的崛起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长期以来一直是理解海洋新物种形成的模型。根据地质资料，海道关闭的最后阶段是在310 - 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）被认为是在地峡形成之前广泛分布在整个热带EP和WA海洋的单一祖先物种的后代。然而，最近的证据提出了问题，关闭CAI实际上如何影响热带美洲的物种多样性模式。考虑到地峡形成后某些种群的灭绝率可能高达70%，研究人员认为在两个大洋中生存的姐妹类群应该很罕见。在EP和WA，如此多的双生物种的明显生存与加勒比海生物大规模更替的古生物学发展图景如何协调？为了回答这个问题，北卡罗来纳州大学的彼得·马尔科博士将对双壳类软体动物Arabiae家族中双生物种复合体的物种形成和灭绝进行分子和古生物学相结合的分析。活体物种将通过核和线粒体基因变异的地理学调查与形态特征的判别分析沿着相结合来判别。化石记录中的物种鉴别将通过将现存动物群中遗传上不同的物种之间形态差异的统计检验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，形态测量和分子遗传学方面的财政支持和培训，并提供资金让学生参加全国会议，以获得展示研究成果的经验。基金还将提供本科教育和分子研究培训的机会，PI将积极从传统上代表性不足的群体中招募个人。虽然没有直接资助这项建议，分子系统发育的工作也将与一个形态系统学家在英国进行的系统发育的努力。

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.