Data from: Specialization and generalization in the diversification of phytophagous insects: tests of the musical chairs and oscillation hypotheses

Evolutionary biologists have often assumed that ecological generalism comes at the expense of less intense exploitation of specific resources and that this trade-off will promote the evolution of ecologically specialized daughter species. Using a phylogenetic comparative approach with butterflies as a model system, we test hypotheses that incorporate changes in niche breadth and location into explanations of the taxonomic diversification of insect herbivores. Specifically, we compare the oscillation hypothesis, where speciation is driven by host-plant generalists giving rise to specialist daughter species, to the musical chairs hypothesis, where speciation is driven by host-plant switching, without changes in niche breadth. Contrary to the predictions of the oscillation hypothesis, we recover a negative relationship between host-plant breadth and diversification rate and find that changes in host breadth are seldom coupled to speciation events. By contrast, we present evidence for a positive relationship between rates of host switching and butterfly diversification, consonant with the musical chairs hypothesis. These results suggest that the costs of trophic generalism in plant-feeding insects may have been overvalued and that transitions from generalists to ecological specialists may not be an important driver of speciation in general.

进化生物学家历来认为，生态广食性会以对特定资源的利用强度减弱为代价，且这种权衡效应将推动生态特化子物种的演化。本研究以蝴蝶为模式系统，采用系统发育比较分析法（phylogenetic comparative approach），检验了将生态位宽度（niche breadth）与位置变化纳入植食性昆虫（insect herbivores）类群分化解释框架的相关假说。具体而言，我们对比了两类假说：其一为振荡假说（oscillation hypothesis），该假说提出物种形成由寄主植物广食者（host-plant generalists）孕育特化子物种所驱动；其二为“抢椅子”假说（musical chairs hypothesis），该假说认为物种形成由寄主植物转换（host-plant switching）所驱动，且生态位宽度未发生改变。与振荡假说的预测相悖，本研究发现寄主植物广食性与分化速率（diversification rate）呈负相关关系，且寄主广度的变化极少与物种形成事件（speciation events）相伴发生。与之相对，我们的研究证据表明寄主转换速率与蝴蝶分化速率呈正相关，这与“抢椅子”假说的结论相符。上述结果提示，植食性昆虫的营养级广食性（trophic generalism）所带来的适应性代价可能被高估，且从广食类群向生态特化类群的转变，总体而言或许并非物种形成的核心驱动因素。