Zoology Department, Swedish Museum of Natural History, Stockholm, Sweden.
Department of Ecology, Environment and Plant Sciences, Stockholm University, Stockholm, Sweden.
Mol Ecol. 2018 Feb;27(4):979-993. doi: 10.1111/mec.14492. Epub 2018 Feb 11.
Changes in morphology are often thought to be linked to changes in species diversification, which is expected to leave a signal of early burst (EB) in phenotypic traits. However, such signal is rarely recovered in empirical phylogenies, even for groups with well-known adaptive radiation. Using a comprehensive phylogenetic approach in Dytiscidae, which harbours ~4,300 species with as much as 50-fold variation in body size among them, we ask whether pattern of species diversification correlates with morphological evolution. Additionally, we test whether the large variation in body size is linked to habitat preference and whether the latter influences species turnover. We found, in sharp contrast to most animal groups, that Dytiscidae body size evolution follows an early-burst model with subsequent high phylogenetic conservatism. However, we found no evidence for associated shifts in species diversification, which point to an uncoupled evolution of morphology and species diversification. We recovered the ancestral habitat of Dytiscidae as lentic (standing water), with many transitions to lotic habitat (running water) that are concomitant to a decrease in body size. Finally, we found no evidence for difference in net diversification rates between habitats nor difference in turnover in lentic and lotic species. This result, together with recent findings in dragonflies, contrasts with some theoretical expectations of the habitat stability hypothesis. Thus, a thorough reassessment of the impact of dispersal, gene flow and range size on the speciation process is needed to fully encompass the evolutionary consequences of the lentic-lotic divide for freshwater fauna.
形态变化通常被认为与物种多样化的变化有关，这预计会在表型特征中留下早期爆发（EB）的信号。然而，即使对于具有明显适应性辐射的群体，这种信号在经验进化枝中也很少被发现。在包含约 4300 种物种的 Dytiscidae 中，我们使用一种综合的系统发育方法，其中物种的体型变化幅度高达 50 倍，我们询问物种多样化的模式是否与形态进化相关。此外，我们还测试了体型的巨大变化是否与栖息地偏好有关，以及后者是否会影响物种更替。与大多数动物群体形成鲜明对比的是，我们发现 Dytiscidae 的体型进化遵循早期爆发模型，随后是高度的系统发育保守性。然而，我们没有发现与物种多样化相关的转变的证据，这表明形态和物种多样化的进化是不相关的。我们恢复了 Dytiscidae 的祖先栖息地为静水（静水），有许多向流水（流水）的过渡，这与体型的减小同时发生。最后，我们没有发现栖息地之间净多样化率的差异，也没有发现静水和流水物种的周转率差异。这一结果与蜻蜓的最新发现相反，与栖息地稳定性假说的一些理论预期相矛盾。因此，需要对扩散、基因流和范围大小对物种形成过程的影响进行全面重新评估，以充分包含淡水动物区系的静水-流水分歧的进化后果。
