Department of Organismic and Evolutionary Biology & Museum of Comparative Zoology, Harvard University, 26 Oxford St,, Cambridge, MA 02134, USA.
BMC Evol Biol. 2011 Jul 21;11:217. doi: 10.1186/1471-2148-11-217.
The rate and mode of lineage diversification might be shaped by clade-specific traits. In Madagascar, many groups of organisms are characterized by tiny distribution ranges and small body sizes, and this high degree of microendemism and miniaturization parallels a high species diversity in some of these groups. We here investigate the geographic patterns characterizing the radiation of the frog family Mantellidae that is virtually endemic to Madagascar. We integrate a newly reconstructed near-complete species-level timetree of the Mantellidae with georeferenced distribution records and maximum male body size data to infer the influence of these life-history traits on each other and on mantellid diversification.
We reconstructed a molecular phylogeny based on nuclear and mitochondrial DNA for 257 species and candidate species of the mantellid frog radiation. Based on this phylogeny we identified 53 well-supported pairs of sister species that we used for phylogenetic comparative analyses, along with whole tree-based phylogenetic comparative methods. Sister species within the Mantellidae diverged at 0.2-14.4 million years ago and more recently diverged sister species had geographical range centroids more proximate to each other, independently of their current sympatric or allopatric occurrence. The largest number of sister species pairs had non-overlapping ranges, but several examples of young microendemic sister species occurring in full sympatry suggest the possibility of non-allopatric speciation. Range sizes of species included in the sister species comparisons increased with evolutionary age, as did range size differences between sister species, which rejects peripatric speciation. For the majority of mantellid sister species and the whole mantellid radiation, range and body sizes were associated with each other and small body sizes were linked to higher mitochondrial nucleotide substitution rates and higher clade diversity. In contrast, small range sizes were unexpectedly associated with a slow-down of mitochondrial substitution rates.
Based on these results we define a testable hypothesis under which small body sizes result in limited dispersal capabilities and low physiological tolerances, causing smaller and more strongly fragmented ranges. This can be thought to facilitate reproductive isolation and thus favor speciation. Contrary to the expectation of the faster speciation of such microendemic phenotype species, we only found small body sizes of mantellid frogs to be linked to higher diversification and substitution rates, but not small range sizes. A joint analysis of various species-rich regional anuran radiations might provide enough species with all combinations of range and body sizes for a more conclusive test of this hypothesis.
谱系多样化的速度和模式可能受到特定分支特征的影响。在马达加斯加，许多生物群系的特征是分布范围极小，体型很小，这种高度的微观特有性和微型化与这些群系中的一些物种多样性相平行。我们在这里研究了几乎完全特有的马达加斯加青蛙家族 Mantellidae 的辐射的地理模式。我们将新重建的 Mantellidae 近完整的种系发生时间树与地理参考分布记录和最大雄性体型数据相结合，以推断这些生活史特征对彼此以及对 Mantellidae 多样化的影响。
我们基于核和线粒体 DNA 为 Mantellidae 青蛙辐射的 257 个物种和候选物种重建了分子系统发育。基于这个系统发育，我们确定了 53 对支持良好的姐妹种，我们使用这些姐妹种进行了系统发育比较分析，以及基于整棵树的系统发育比较方法。Mantellidae 内的姐妹种在 0.2-14.4 百万年前分化，最近分化的姐妹种的地理范围中心彼此更接近，而与它们当前的同域或异域发生无关。最大数量的姐妹种对具有不重叠的范围，但几个年轻的微特有姐妹种在完全同域中出现的例子表明了非异域物种形成的可能性。包括在姐妹种比较中的物种的范围大小随进化年龄而增加，姐妹种之间的范围大小差异也是如此，这拒绝了邻域物种形成。对于 Mantellidae 姐妹种的大多数和整个 Mantellidae 辐射，范围和体型彼此相关，较小的体型与更高的线粒体核苷酸取代率和更高的分支多样性相关。相比之下，小的范围大小与线粒体取代率的减缓有关。
基于这些结果，我们定义了一个可测试的假设，即小体型导致有限的扩散能力和低生理耐受性，导致更小和更强烈碎片化的范围。这可以被认为有助于生殖隔离，从而有利于物种形成。与微特有表型物种更快的物种形成的预期相反，我们只发现 Mantellidae 青蛙的小体型与更高的多样性和取代率相关，而不是小范围大小。对各种物种丰富的区域无尾两栖动物辐射的联合分析可能会为具有各种范围和体型的足够物种提供足够的样本，以更具结论性地检验这一假设。
