Ornelas-García Claudia Patricia, Domínguez-Domínguez Omar, Doadrio Ignacio
Departamento de Biodiversidad y Biología Evolutiva, Museo Nacional de Ciencias Naturales, CSIC, José Gutiérrez Abascal 2, Madrid, Spain.
BMC Evol Biol. 2008 Dec 22;8:340. doi: 10.1186/1471-2148-8-340.
Mesoamerica is one of the world's most complex biogeographical regions, mostly due to its complex geological history. This complexity has led to interesting biogeographical processes that have resulted in the current diversity and distribution of fauna in the region. The fish genus Astyanax represents a useful model to assess biogeographical hypotheses due to it being one of the most diverse and widely distributed freshwater fish species in the New World. We used mitochondrial and nuclear DNA to evaluate phylogenetic relationships within the genus in Mesoamerica, and to develop historical biogeographical hypotheses to explain its current distribution.
Analysis of the entire mitochondrial cytochrome b (Cytb) gene in 208 individuals from 147 localities and of a subset of individuals for three mitochondrial genes (Cytb, 16 S, and COI) and a single nuclear gene (RAG1) yielded similar topologies, recovering six major groups with significant phylogeographic structure. Populations from North America and Upper Central America formed a monophyletic group, while Middle Central America showed evidence of rapid radiation with incompletely resolved relationships. Lower Central America lineages showed a fragmented structure, with geographically restricted taxa showing high levels of molecular divergence. All Bramocharax samples grouped with their sympatric Astyanax lineages (in some cases even with allopatric Astyanax populations), with less than 1% divergence between them. These results suggest a homoplasic nature to the trophic specializations associated with Bramocharax ecomorphs, which seem to have arisen independently in different Astyanax lineages. We observed higher taxonomic diversity compared to previous phylogenetic studies of the Astyanax genus. Colonization of Mesoamerica by Astyanax before the final closure of the Isthmus of Panama (3.3 Mya) explains the deep level of divergence detected in Lower Central America. The colonization of Upper Mesoamerica apparently occurred by two independent routes, with lineage turnover over a large part of the region.
Our results support multiple, independent origins of morphological traits in Astyanax, whereby the morphotype associated with Bramocharax represents a recurrent trophic adaptation. Molecular clock estimates indicate that Astyanax was present in Mesoamerica during the Miocene (approximately 8 Mya), which implies the existence of an incipient land-bridge connecting South America and Central America before the final closure of the Isthmus of Panama (approximately 3.3 Mya).
中美洲是世界上生物地理最为复杂的区域之一，主要归因于其复杂的地质历史。这种复杂性导致了有趣的生物地理过程，进而形成了该地区目前动物群的多样性和分布格局。阿氏霓虹脂鲤属鱼类是评估生物地理假说的一个有用模型，因为它是新世界中最多样化且分布最广的淡水鱼物种之一。我们利用线粒体和核DNA来评估中美洲该属内的系统发育关系，并提出历史生物地理假说以解释其当前分布。
对来自147个地点的208个个体的整个线粒体细胞色素b（Cytb）基因以及部分个体的三个线粒体基因（Cytb、16S和COI）和一个核基因（RAG1）进行分析，得到了相似的拓扑结构，识别出六个具有显著系统地理结构的主要类群。来自北美洲和中美洲上部的种群形成一个单系类群，而中美洲中部则显示出快速辐射的证据，其关系尚未完全解析。中美洲下部的谱系呈现出碎片化结构，地理分布受限的类群表现出高水平的分子分化。所有布拉莫霓虹脂鲤样本与其同域分布的阿氏霓虹脂鲤谱系归为一类（在某些情况下甚至与异域分布的阿氏霓虹脂鲤种群归为一类），它们之间的差异小于1%。这些结果表明，与布拉莫霓虹脂鲤生态型相关的营养特化具有同塑性，似乎是在不同的阿氏霓虹脂鲤谱系中独立出现的。与之前对阿氏霓虹脂鲤属的系统发育研究相比，我们观察到了更高的分类多样性。在巴拿马地峡最终闭合（330万年前）之前，阿氏霓虹脂鲤对中美洲的殖民解释了在中美洲下部检测到的深度分化。中美洲上部的殖民显然是通过两条独立的路线发生的，在该地区的大部分区域都有谱系更替。
我们的结果支持阿氏霓虹脂鲤形态特征的多个独立起源，其中与布拉莫霓虹脂鲤相关的形态型代表了一种反复出现的营养适应。分子钟估计表明，阿氏霓虹脂鲤在中新世（约800万年前）就已存在于中美洲，这意味着在巴拿马地峡最终闭合（约330万年前）之前，存在一条连接南美洲和中美洲的初始陆桥。
