Data from: The grass was greener: repeated evolution of specialized morphologies and habitat shifts in ghost spiders following grassland expansion in South America

While grasslands, one of Earth’s major biomes, are known for their close evolutionary ties with ungulate grazers, these habitats are also paramount to the origins and diversification of other animals. Within the primarily South American spider subfamily Amaurobioidinae (Anyphaenidae), several species are found living in the continent’s grasslands, with some displaying putative morphological adaptations to dwelling unnoticed in the grass blades. Here, a dated molecular phylogeny provides the backbone for analyses revealing the ecological and morphological processes behind these spiders’ grassland adaptations. The multiple switches from Patagonian forests to open habitats coincide with the expansion of South America’s grasslands during the Miocene, while the specialized morphology of several grass-dwelling spiders originated at least three independent times and is best described as the result of different selective regimes operating on macroevolutionary timescales. Although grass-adapted lineages evolved towards different peaks in adaptive landscape, they all share one characteristic: an anterior narrowing of the prosoma allowing spiders to extend the first two pairs of legs, thus maintaining a slender resting posture in the grass blade. By combining phylogenetic, morphological, and biogeographic perspectives we disentangle multiple factors determining the evolution of a clade of terrestrial invertebrate predators alongside their biomes.草原作为地球主要生物群系（biome）之一，素来以与有蹄类植食动物的紧密演化关联为人熟知，而这类生境对于其他动物的起源与物种分化同样至关重要。在以南美洲为分布核心的管巢蛛科（Anyphaenidae）类盲蛛亚科（Amaurobioidinae）蜘蛛类群中，已有多个物种被记录栖息于该大陆的草原生境，其中部分物种展现出疑似适应在草叶间隐蔽栖息的形态特征。本研究通过带有时间校准的分子系统发育树作为分析核心框架，揭示了这类蜘蛛适应草原生境背后的生态与形态演化过程。从巴塔哥尼亚森林向开阔生境的多次生境转换，与中新世（Miocene）时期南美洲草原的扩张进程高度重合；而数种栖息于草原的蜘蛛所特有的形态特征，至少独立起源了三次，该特征最合理的解释是在宏观演化时间尺度上，不同选择机制共同作用的结果。尽管适应草原生境的演化支（clade）在适应性景观（adaptive landscape）中朝向不同的适应峰演化，但它们均具备一项共同特征：头胸部（prosoma）前端收窄，使得蜘蛛能够伸展前两对步足，从而在草叶间保持纤细的休憩姿态。本研究结合系统发育、形态学与生物地理学视角，厘清了调控一类陆生无脊椎捕食者类群及其伴随生境共同演化的多重因素。