Data from: Digging their own macroevolutionary grave: Fossoriality as an evolutionary dead-end in snakes

The tree of life is highly asymmetrical in its clade wise species richness and this has often been attributed to variation in diversification rates either across time or lineages. Variations across lineages are usually associated with traits that increase lineage diversification. Certain traits can also hinder diversification by increasing extinction and such traits are called evolutionary dead-ends. Ecological specialization has usually been considered as an evolutionary dead-end. However, recent analyses of specializations along single axes have provided mixed support for this model. Here, we test if fossoriality, a trait that forces specialization at multiple axes, acts as an evolutionary dead-end in squamates (lizards and snakes) using recently developed phylogenetic comparative methods. We show that fossoriality is an evolutionary dead-end in snakes but not in lizards. Fossorial snakes exhibit reduced speciation and increased extinction compared to non-fossorial snakes. Our analysis also indicates that transition rates from fossoriality to non-fossoriality in snakes are significantly lower than transition rates from non-fossoriality to fossoriality. Overall our results suggest that broad scale ecological interactions that lead to specialization at multiple axes limit diversification.

生命之树在各演化支（clade）的物种丰富度上呈现高度不对称性，该现象常被归因于不同时间或不同演化支间的多样化速率差异。演化支间的多样化速率差异通常与提升支系多样化能力的性状相关。部分性状还会通过提高灭绝风险阻碍物种多样化，这类性状被称为进化死端（evolutionary dead-end）。生态特化通常被视作一种进化死端。然而，近期针对单维度特化的分析对这一假说提供了混杂的支持证据。本研究借助新近开发的系统发育比较方法，检验穴居性（fossoriality）——一种迫使生物在多维度上发生特化的性状——在有鳞类（squamates，即蜥蜴与蛇类）中是否属于进化死端。研究结果表明，穴居性在蛇类中属于进化死端，但在蜥蜴中并非如此。与非穴居蛇类相比，穴居蛇类的物种形成速率更低、灭绝速率更高。本研究的分析还显示，蛇类从穴居性向非穴居性的演化转换速率，显著低于其从非穴居性向穴居性的转换速率。综合来看，本研究结果表明，能够导致生物在多维度上发生特化的大范围生态相互作用会限制物种多样化。