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

Phylogenetic niche conservatism (PNC) shapes the distribution of organisms by constraining lineages to particular climatic conditions. Conversely, if areas with similar climates are geographically isolated, diversification may also be limited by dispersal. Neotropical xeric habitats provide an ideal system to test the relative roles of climate and geography on diversification, as they occur in disjunct areas with similar biotas. Sicariinae sand spiders 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 explore the role of PNC, geography and biome shifts in their evolution and timing of diversification. We estimated a time-calibrated, total-evidence phylogeny of Sicariinae, and used published distribution records to estimate climatic niche and biome occupancy. Topologies were used for estimating ancestral niches and biome shifts. We used variation partitioning methods to test the relative importance of climate and spatially autocorrelated factors in explaining the spatial variation in phylogenetic structure of Sicarius across the Neotropics. Neotropical Sicarius are ancient and split from their African sister-group around 90 (57-131) million years ago. Most speciation events took place in the Miocene. Sicariinae records can be separated in two groups corresponding to temperate/dry and tropical/seasonally dry climates. The ancestral climatic niche of Sicariinae are temperate/dry areas, with 2-3 shifts to tropical/seasonally dry areas in Sicarius. Similarly, ancestral biomes occupied by the group 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 ancient association to arid lands, suggesting that PNC prevented them from colonizing mesic habitats. However, niches are labile at a smaller scale, with several shifts from deserts to SDTFs. This suggests that PNC and long-distance dispersal limitation played major roles in confining lineages to isolated areas of SDTF/desert over evolutionary history, although shifts between xeric biomes occurred whenever geographical opportunities were presented.

Demographical history and palaeodistribution modelling show range shift towards Amazon Basin for a Neotropical tree species in the LGM.

BACKGROUND: We studied the phylogeography and demographical history of Tabebuia serratifolia (Bignoniaceae) to understand the disjunct geographical distribution of South American seasonally dry tropical forests (SDTFs). We specifically tested if the multiple and isolated patches of SDTFs are current climatic relicts of a widespread and continuously distributed dry forest during the last glacial maximum (LGM), the so called South American dry forest refugia hypothesis, using ecological niche modelling (ENM) and statistical phylogeography. We sampled 235 individuals of T. serratifolia in 17 populations in Brazil and analysed the polymorphisms at three intergenic chloroplast regions and ITS nuclear ribosomal DNA. RESULTS: Coalescent analyses showed a demographical expansion at the last c. 130 ka (thousand years before present). Simulations and ENM also showed that the current spatial pattern of genetic diversity is most likely due to a scenario of range expansion and range shift towards the Amazon Basin during the colder and arid climatic conditions associated with the LGM, matching the expected for the South American dry forest refugia hypothesis, although contrasting to the Pleistocene Arc hypothesis. Populations in more stable areas or with higher suitability through time showed higher genetic diversity. Postglacial range shift towards the Southeast and Atlantic coast may have led to spatial genome assortment due to leading edge colonization as the species tracks suitable environments, leading to lower genetic diversity in populations at higher distance from the distribution centroid at 21 ka. CONCLUSION: Haplotype sharing or common ancestry among populations from Caatinga in Northeast Brazil, Atlantic Forest in Southeast and Cerrado biome and ENM evince the past connection among these biomes.

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

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