Out of north Africa: Evolution and biogeography of Afro-Arabian dwarf tarantulas (Theraphosidae, Ischnocolinae)

Large-scale vicariant events are expected to create congruent
phylogeographic patterns among unrelated taxa. A continental-wide
disjunction displayed by unrelated plant taxa across Afro-Arabia (the RAND
flora pattern) has been traditionally explained as a consequence of late
Miocene aridification of the region and the formation of the Sahara
Desert. We implement genomic data (UCE), divergence time estimation and
biogeographic analyses to uncover the origins of RAND pattern distribution
in dwarf tarantula genus Ischnocolus Ausserer, 1871. The results suggest
that the disjunct distribution of Ischnocolus resulted from ecological
vicariance driven by the Middle Miocene climate cooling, predating the
timing of the aridification of the region. Our results thus bring evidence
of phylogeographic discordance of the RAND pattern origins among different
taxa. Conserved lifestyle and the preference for humid environments among
the early diverging Ischnocolus lineages also suggest that dispersal
across Afro-Arabia was likely catalyzed by interspecific competitive
exclusion. Subsequent lifestyle switches, that enabled the dwarf
tarantulas to successfully colonize dry environments, evolved repeatedly
in the group’s evolution. Additionally, we delimit the boundaries of the
genus Ischnocolus and assess its position within the tarantula phylogeny.
As a consequence, we revalidate the genus Luphocemus Denis, 1960, which is
endemic to North Africa.