Malato Grace, Shervette Virginia R, Navarrete Amaya Ronald, Valdiviezo Rivera Jonathan, Nugra Salazar Fredy, Calle Delgado Paola, Karpan Kirby C, Aguirre Windsor E
Department of Biological Sciences, DePaul University, Chicago, Illinois, United States of America.
Department of Biology/Geology, University of South Carolina, Aiken, South Carolina, United States of America.
PLoS One. 2017 Jun 28;12(6):e0179432. doi: 10.1371/journal.pone.0179432. eCollection 2017.
Neotropical mountain streams are important contributors of biological diversity. Two species of the characid genus Rhoadsia differing for an ecologically important morphological trait, body depth, have been described from mountain streams of the western slopes of the Andes in Ecuador. Rhoadsia altipinna is a deeper-bodied species reported from low elevations in southwestern Ecuador and northern Peru, and Rhoadsia minor is a more streamlined species that was described from high elevations (>1200 m) in the Esmeraldas drainage in northwestern Ecuador. Little is known about these species and their validity as distinct species has been questioned. In this study, we examine how their body shape varies along replicated elevational gradients in different drainages of western Ecuador using geometric morphometrics and the fineness ratio. We also use sequences of the mitochondrial cytochrome oxidase c I gene and the second intron of the S7 nuclear gene to examine whether genetic data are consistent with the existence of two species. We found that body depth varies continuously among populations within drainages as a function of elevation, and that body shape overlaps among drainages, such that low elevation populations of R. minor in the Esmeraldas drainage have similar body depths to higher elevation R. altipinna in southern drainages. Although a common general trend of declining body depth with elevation is clear, the pattern and magnitude of body shape divergence differed among drainages. Sequencing of mitochondrial and nuclear genes failed to meet strict criteria for the recognition of two species (e.g., reciprocal monophyly and deep genetic structure). However, there was a large component of genetic variation for the COI gene that segregated among drainages, indicating significant genetic divergence associated with geographic isolation. Continued research on Rhoadsia in western Ecuador may yield significant insight into adaptation and speciation in Neotropical mountain streams.
新热带山区溪流是生物多样性的重要贡献者。在厄瓜多尔安第斯山西坡的山区溪流中，已描述了脂鲤属Rhoadsia的两个物种，它们在一个具有重要生态意义的形态特征——体深方面存在差异。高鳍Rhoadsia altipinna是一种体深较深的物种，分布于厄瓜多尔西南部和秘鲁北部的低海拔地区，而小Rhoadsia minor是一种体型更流线型的物种，是从厄瓜多尔西北部埃斯梅拉达斯河流域的高海拔地区（>1200米）描述的。人们对这些物种知之甚少，它们作为不同物种的有效性也受到了质疑。在本研究中，我们使用几何形态测量学和细长度比率，研究了它们的体型在厄瓜多尔西部不同流域重复的海拔梯度上如何变化。我们还使用线粒体细胞色素氧化酶c I基因和S7核基因的第二个内含子序列，来检验遗传数据是否与两个物种的存在一致。我们发现，流域内种群的体深随海拔高度连续变化，且不同流域的体型存在重叠，例如埃斯梅拉达斯河流域低海拔的小Rhoadsia minor种群的体深与南部流域高海拔的高鳍Rhoadsia altipinna相似。尽管随着海拔升高体深下降的总体趋势很明显，但不同流域体型差异的模式和程度有所不同。线粒体和核基因测序未能满足识别两个物种的严格标准（例如，相互单系性和深度遗传结构）。然而，COI基因存在很大一部分遗传变异，这些变异在不同流域间分离，表明与地理隔离相关的显著遗传分化。对厄瓜多尔西部Rhoadsia的持续研究可能会对新热带山区溪流的适应和物种形成产生重要见解。
