The Grass was Greener: Repeated Evolution of Specialized Morphologies and Habitat Shifts in Ghost Spiders Following Grassland Expansion in South America

CECCARELLI, F SARA; KOCH, NICOLÁS MONGIARDINO; SOTO, EDUARDO M; BARONE, MARIANA L; ARNEDO, MIQUEL A; RAMÍREZ, MARTÍN J

SYSTEMATIC BIOLOGY

OXFORD UNIV PRESS

Año: 2019 vol. 68 p. 63 - 77

1063-5157

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 Americanspider subfamily Amaurobioidinae (Anyphaenidae), several species are found living in the continent?s grasslands, withsome displaying putative morphological adaptations to dwelling unnoticed in the grass blades. Herein, a dated molecularphylogeny 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 SouthAmerica?s grasslands during theMiocene, while the specialized morphology of several grass-dwelling spiders originated atleast three independent times and is best described as the result of different selective regimes operating on macroevolutionarytimescales. Although grass-adapted lineages evolved towards different peaks in adaptive landscape, they all share onecharacteristic: an anterior narrowing of the prosoma allowing spiders to extend the first two pairs of legs, thus maintaininga slender resting posture in the grass blade. By combining phylogenetic, morphological, and biogeographic perspectiveswe disentangle multiple factors determining the evolution of a clade of terrestrial invertebrate predators alongside theirbiomes.