The tangled biogeographic history of tarantulas: An African centre of origin rules out the centrifugal model of speciation

AimMany animal groups diversify at the same place where they have originated, whereas others diversify at a place completely different from the centre of origin. Identification of the centre of origin, subsequent colonisation and diversification is crucial for understanding lineages' macroevolutionary dynamics and biogeographical patterns. The historical biogeography of the Mygalomorph spider family Theraphosidae has been confounded by two conflicting hypotheses - a South American origin for the group, which is also the centre of its greatest extant diversity, as against an African origin. We aim to ascertain the centre of origin and directionality of inter-continental dispersal events in tarantulas by reconstructing their biogeographic history. LocationWorldwide. TaxonTarantulas. MethodsWe calibrated a previously published genome-scale phylogeny of Mygalomorph spiders using an improved interpretation of the fossil record. We reconstructed ancestral geographic ranges using the R package biogeobears to explicitly test four different hypotheses that are likely to explain the extant diversity and distribution of tarantulas incorporating a time-stratified approach. ResultsOur results indicate that the ancestral stock of extant tarantulas occurred in Africa and South America during the mid-Cretaceous, but subsequently went extinct in South America. This points to an African origin for all modern tarantula lineages. The best supported biogeographic model suggests multiple 'out of Africa' dispersal events into South America and later into India during the late Cretaceous. Main ConclusionLocalised ecological processes such as extinction, dispersal, key innovations, hybridisation and species-area relationships might cause a discordance between centre of origin and diversity.