Did a Miocene-Pliocene island isolation sequence structure diversification of funnel web spiders in the Taiwan-Ryukyu Archipelago?

Aim: We tested the competing hypotheses concerning the relative importance of Pleistocene versus Miocene-Pliocene geological events for the formation of endemism in an Asian archipelago using the Macrothele taiwanensis (Hexathelidae) species group. Location: Taiwan-Ryukyu Archipelago. Methods: We estimated phylogenetic trees from cytochrome oxidase I subunit (COI) and 16S rRNA (16S) gene regions and employed Bayesian ancestral range reconstructions to investigate previously debated models of lineage diversification in the Taiwan-Ryukyu Archipelago. To evaluate alternative geological timeframes for their importance in shaping the genetic structure of funnel web spiders, we used five time calibration schemes to estimate timing of divergence, infer ancestral distributions, and to reconstruct historical demographic changes in each lineage. We tested taxonomic boundaries with two species delimitation procedures. Results: Our results indicate a north-to-south isolation sequence of the M. taiwanensis group: the Amami lineage diverged first, then Yaeyama, and finally the Taiwanese lineages. Divergence time estimation and population demographic change analyses indicate that Pleistocene climate fluctuations minimally impacted the genetic structure of these spiders. Instead, estimated divergence events correspond to Miocene-Pliocene geological events, strongly supporting a much older timeframe for diversification. The results of species delimitation analyses coincide well with morphological differences observed among the island populations, reinforcing inferred species boundaries, and at least three potential cryptic species were statistically detected within Taiwan. Main conclusions: Miocene-Pliocene geological events appear to have contributed disproportionately to diversification in the M. taiwanensis species group. The clear association between geographical area, genetic structure and statistical species delimitation strongly supports an interpretation of allopatric speciation. We advocate comparing our results with those derived from additional study organisms with similar life histories to further explore the Miocene-Pliocene diversification hypothesis.