Complex inter-island colonization and peripatric founder speciation promote diversification of flightless Pachyrhynchus weevils in the Taiwan–Luzon volcanic belt

Aim: We investigated the spatial and temporal patterns of diversification among colourful and flightless weevils, the Pachyrhynchus orbifer complex, to test the stepping-stone hypothesis of colonization across the Taiwan–Luzon volcanic belt. Location: Southeast Asia. Methods: The phylogeny of the P. orbifer complex was reconstructed from a multi-locus data set of mitochondrial and nuclear genes using maximum likelihood in RAxML and Bayesian inference in MRBAYES. Likelihood-based tests in CONSEL were used to evaluate alternative tree topologies. Divergence times were estimated in beast based on a range of mutation rates. Ancestral range and biogeographical history were reconstructed using Bayesian binary MCMC (BBM) methods in RASP and in BioGeoBEARS. Demographic histories were inferred using the extended Bayesian skyline plot (EBSP). Species boundaries were tested using BPP. Results: The phylogeny of the P. orbifer complex indicated strong support for seven reciprocally monophyletic lineages grouped by current island boundaries (Camiguin, Fuga, Dalupiri, Calayan, Babuyan, Orchid and Yaeyama Islands), except for a sister Green + Itbayat lineage. Complex and stochastic colonization of P. orbifer was inferred to have involved both northward and southward directions with short- and long-distance dispersal events, which are strongly inconsistent with the strict stepping-stone hypothesis. Divergence time estimates for all extant island lineages (<1 Myr of Middle Pleistocene) are much more recent than the geological ages (22.4–1.7 Myr) and subaerial existence (c. 3 Myr) of the islands. The statistically delimited seven cryptic species imply that the diversity of Pachyrhynchus from small peripheral islands continues to be largely under-estimated. Main conclusions: The non-linear, more complex spatial and temporal settings of the archipelago and stochastic dispersal were probable key factors shaping the colonization history of the P. orbifer complex. Speciation of the P. orbifer complex may have occurred only between islands, indicating that peripatric speciation through the founders of stochastic dispersals was the major evolutionary driver.