Phylogeny of Neotropical Sicarius sand spiders suggests frequent transitions from deserts to dry forests despite antique, broad-scale niche conservatism

ABSTRACT

Phylogenetic niche conservatism (PNC) shapes the distribution of organisms by constraining lineages to parti-cular climatic conditions. Conversely, if areas with similar climates are geographically isolated, diversificationmay also be limited by dispersal. Neotropical xeric habitats provide an ideal system to test the relative roles ofclimate and geography on diversification, as they occur in disjunct areas with similar biotas. Sicariinae sandspiders are intimately associated with these xeric environments, particularly seasonally dry tropical forests(SDTFs) and subtropical deserts/scrublands in Africa (Hexophthalma) and the Neotropics (Sicarius). We explorethe role of PNC, geography and biome shifts in their evolution and timing of diversification. We estimated atime-calibrated, total-evidence phylogeny of Sicariinae, and used published distribution records to estimateclimatic niche and biome occupancy. Topologies were used for estimating ancestral niches and biome shifts. Weused variation partitioning methods to test the relative importance of climate and spatially autocorrelatedfactors in explaining the spatial variation in phylogenetic structure ofSicariusacross the Neotropics. NeotropicalSicariusare ancient and split from their African sister-group around 90 (57–131) million years ago. Most spe-ciation events took place in the Miocene. Sicariinae records can be separated in two groups corresponding totemperate/dry and tropical/seasonally dry climates. The ancestral climatic niche of Sicariinae are temperate/dryareas, with 2–3 shifts to tropical/seasonally dry areas inSicarius. Similarly, ancestral biomes occupied by thegroup are temperate and dry (deserts, Mediterranean scrub, temperate grasslands), with 2–3 shifts to tropical,seasonally dry forests and grasslands. Most of the variation in phylogenetic structure is explained by long-distance dispersal limitation that is independent of the measured climatic conditions. Sicariinae have an ancientassociation to arid lands, suggesting that PNC prevented them from colonizing mesic habitats. However, nichesare labile at a smaller scale, with several shifts from deserts to SDTFs. This suggests that PNC and long-distancedispersal limitation played major roles in confining lineages to isolated areas of SDTF/desert over evolutionaryhistory, although shifts between xeric biomes occurred whenever geographical opportunities were presented