Institute of Zoology, University of Veterinary Medicine, Bünteweg 17, 30559 Hannover, Germany.
BMC Evol Biol. 2010 May 18;10:146. doi: 10.1186/1471-2148-10-146.
Uncovering how populations of a species differ genetically and ecologically is important for understanding evolutionary processes. Here we combine population genetic methods (microsatellites) with phylogenetic information (mtDNA) to define genetic population clusters of the wide-spread Neotropical túngara frog (Physalaemus pustulosus). We measure gene flow and migration within and between population clusters and compare genetic diversity between population clusters. By applying ecological niche modeling we determine whether the two most divergent genetic groups of the túngara frog (1) inhabit different habitats, and (2) are separated geographically by unsuitable habitat across a gap in the distribution.
Most population structure is captured by dividing all sample localities into two allopatric genetic lineages. The Northern genetic lineage (NW Costa Rica) is genetically homogenous while the Southern lineage (SW Costa Rica and Panama) is sub-divided into three population clusters by both microsatellite and mtDNA analyses. Gene flow is higher within the Northern lineage than within the Southern lineage, perhaps due to increased landscape heterogeneity in the South. Niche modeling reveals differences in suitable habitat between the Northern and Southern lineages: the Northern lineage inhabits dry/pine-oak forests, while the Southern lineage is confined to tropical moist forests. Both lineages seem to have had little movement across the distribution gap, which persisted during the last glacial maximum. The lack of movement was more pronounced for the Southern lineage than for the Northern lineage.
This study confirms the finding of previous studies that túngara frogs diverged into two allopatric genetic lineages north and south of the gap in the distribution in central Costa Rica several million years ago. The allopatric distribution is attributed to unsuitable habitat and probably other unknown ecological factors present across the distribution gap. Niche conservatism possibly contributes to preventing movements across the gap and gene flow between both groups. Genetic and ecological data indicate that there is the potential for ecological divergence in allopatry between lineages. In this context we discuss whether the Northern and Southern lineages should be recognized as separate species, and we conclude that further studies of pre- and post-zygotic isolation are needed for a final assessment. Identified population clusters should motivate future behavioral and ecological research regarding within-species biodiversity and speciation mechanisms.
揭示一个物种的遗传和生态差异对于理解进化过程非常重要。在这里，我们结合群体遗传方法（微卫星）和系统发育信息（mtDNA）来定义广泛分布的新热带雨蛙（Physalaemus pustulosus）的遗传种群聚类。我们测量种群内和种群间的基因流动和迁移，并比较种群间的遗传多样性。通过应用生态位模型，我们确定雨蛙的两个最具遗传差异的群体（1）是否栖息在不同的栖息地，以及（2）是否由于分布中断的不适合栖息地而在地理上分离。
大多数种群结构是通过将所有样本地点划分为两个地理上隔离的遗传谱系来捕捉的。北方遗传谱系（NW 哥斯达黎加）在遗传上是同质的，而南方谱系（SW 哥斯达黎加和巴拿马）则通过微卫星和 mtDNA 分析分为三个种群聚类。北方谱系内的基因流动高于南方谱系内的基因流动，这可能是由于南方的景观异质性增加所致。生态位模型揭示了北方和南方谱系之间适宜栖息地的差异：北方谱系栖息在干燥/松-栎林中，而南方谱系则局限于热带湿润森林中。这两个谱系似乎都很少跨越分布缺口移动，而这个缺口在末次冰期最大值期间一直存在。南方谱系的移动性比北方谱系更为明显。
本研究证实了先前研究的发现，即雨蛙在中哥斯达黎加分布缺口的南北两侧分化为两个地理上隔离的遗传谱系，这一过程发生在几百万年前。这种地理上的隔离归因于不适宜的栖息地以及分布缺口处可能存在的其他未知生态因素。生态位保守主义可能有助于阻止两个群体之间的缺口跨越和基因流动。遗传和生态数据表明，在地理隔离中，谱系之间存在生态分歧的潜力。在这种情况下，我们讨论了北方和南方谱系是否应被视为独立的物种，并得出结论，需要进一步研究合子前和合子后的隔离，以做出最终评估。确定的种群聚类应该激发未来关于物种内生物多样性和物种形成机制的行为和生态研究。
