Why do taxa differ in species richness? A multifactorial evolutionary view at species richness disparities in microgastropods

物种丰富度的显着差异，在生物系统发育的分支已被归因于分支年龄的差异或多样化率（物种形成减去灭绝），这是由外在（如栖息地类型，地理分布和物种共现）和/或内在（如形态特征）的因素驱动的变化。虽然进化枝年龄似乎是一个简单的标准丰富的差异，多样性的内在和外在的驱动因素仍然没有得到很好的理解。以往的研究通常集中在单一因素对多元化率的影响上。然而，各种因素对多样化率的影响可能是复杂的依赖，这表明需要进行多因素分析。此外，我们目前的丰富度差异的进化理解是强烈偏向于海洋或陆地系统，脊椎动物，和/或小的分类群体。该项目的主要目标是测试驱动程序的物种丰富度的差异，使用分类学和生态多样性的模式分类（水生腹足类家庭Hydrobiidae）和一种新的多因子系统发育比较方法，使这些外在和内在因素的联合作用的估计。将构建一个稳健的时间校准的物种发生学（基于>400个物种的多位点DNA序列数据），以推断物种形成、灭绝和随时间推移和分支之间的净多样化率。上述外在和内在因素对多样化率的影响将分别使用系统发育比较分析和这些变量的联合影响进行研究，将利用多因子系统发育模型进行评估。我们将采用的这一新方法将增加我们对淡水生物多样化驱动因素的了解，也可能更广泛地作为一个新的概念和方法基础，用于比较生命之树内部和不同领域之间多样化的模式和原因。此外，我们的研究结果可能有助于制定一个更严格的框架，优先考虑内陆水生生态系统的保护政策。

The striking differences in species richness across phylogenetic clades of organisms has been attributed to differences in clade age or to variation in diversification rates (speciation minus extinction), which is driven by extrinsic (e.g. habitat type, geographic distribution, and species co-occurrence) and/or intrinsic (e.g. morphological features) factors. Whereas clade age appears to be a straight-forward criterion for richness differences, the intrinsic and extrinsic drivers of diversification remain not well understood. Previous studies have usually focused on the influence of single factors on diversification rate. However, the effect of various factors on diversification rates may be complexly dependent, which suggests a need for multifactorial analyses. Moreover, our current evolutionary understanding of richness differences is strongly biased towards marine or terrestrial systems, vertebrates, and/or small taxonomic groups. The main goal of this project is to test for drivers of species richness disparities using a taxonomically and ecologically diverse model taxon (the aquatic gastropod family Hydrobiidae) and a novel multifactorial phylogenetic comparative approach that enables estimation of the joint effect of these extrinsic and intrinsic factors. A robust time calibrated phylogeny will be constructed (based on multi locus DNA sequence data for >400 species) to infer speciation, extinction, and net diversification rates over time and among clades. The effects of the above mentioned extrinsic and intrinsic factors on diversification rates will be studied individually using phylogenetic comparative analyses and the joint influence of these variables will be assessed utilizing a multifactorial phylogenetic model. This novel approach that we will utilize will increase our knowledge of the drivers of diversification in freshwater organisms and may also serve more broadly as a new conceptual and methodological basis for comparing patterns and causes of diversification within the tree of life and among different realms. Additionally, our findings may contribute to the development of a more rigorous framework for the prioritization of conservation policies in inland aquatic ecosystems.