Phylogeography of the dry vegetation endemic species Nephila sexpunctata (Araneae: Araneidae) suggests recent expansion of the Neotropical Dry Diagonal

Abstract

Aim The Neotropical Dry Diagonal (DD) is a corridor of distinct dry environments in central South America. The main hypotheses suggest that these environments may have expanded during the glacial cycles together with a retraction of rainforests, and then shrank when the climate became wetter and warmer. However, few studies have explicitly tested the hypotheses on DD evolution. We conducted a phylogeographical study on Nephila sexpunctata, a spider endemic to Neotropical dry habitats, to enrich the understanding of DD evolutionary history. Location South-western portion of the DD (Cerrado and Chaco). Methods We sequenced two mitochondrial regions and one nuclear DNA region of 65 individuals from 10 locations across the species' range. We conducted analyses of genetic structure, variability, demography and inferred divergence times. We used an ecological niche modelling framework to generate hypotheses on the species' distribution along the last glacial cycle and a model-based approach to test the demographical scenarios that might explain the genetic patterns. Results Both markers presented low genetic diversity. Mitochondrial markers had high genetic structure, with specific geographical lineages within each biome, while the nuclear marker presented low genetic structure. Phylogeo-graphical and demographical events encompass the last glacial cycle, with a strong post-Last Glacial Maximum (LGM) population and spatial expansion. Model testing corroborated the recent demographical expansion of N. sexpunctata. Main Conclusions Our data suggest that Quaternary climate cycles, when moist forests periodically expanded towards the dry vegetation, influenced the diversification of DD organisms by promoting demographical events. These events might explain the genetic structure observed in N. sexpunctata; differently from what was expected by the Pleistocene refugia model, some DD species may have experienced post-LGM expansion. Climate and geological events have both affected DD-endemic organisms' diversification.