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The Brazilian Caatinga is part of the seasonally dry tropical forests, a
vegetation type disjunctly distributed throughout the Neotropics. It has
been suggested that during Pleistocene glacial periods, these dry forests
had a continuous distribution, so that these climatic shifts may have
acted as important driving forces of the Caatinga biota diversification.
To address how these events affected the distribution of a dry forest
species, we chose Sicarius cariri, a spider endemic to the Caatinga, as a
model. We studied the phylogeography of one mitochondrial and one nuclear
gene and reconstructed the paleodistribution of the species using
modelling algorithms. We found two allopatric and deeply divergent clades
within S. cariri, suggesting that this species as currently recognized
might consist of more than one independently evolving lineage. Sicarius
cariri populations are highly structured, with low haplotype sharing among
localities, high fixation index and isolation by distance. Models of
paleodistribution, Bayesian reconstructions and coalescent simulations
suggest that this species experienced a reduction in its population size
during glacial periods, rather than the expansion expected by previous
hypotheses on the paleodistribution of dry forest taxa. In addition to
that, major splits of intraspecific lineages of S. cariri took place in
the Pliocene. Taken together, these results indicate S. cariri has a
complex diversification history dating back to the Tertiary, suggesting
the history of dry forest taxa may be significantly older than previously
thought.
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