Global biogeographical pattern of swallowtail diversification demonstrates alternative colonization routes in the Northern and Southern hemispheres
Résumé
AIM Swallowtail butterflies (Papilionidae) are a diverse and widespread group of insects that constitute a popular model system for ecological and evolutionary studies. We reconstruct the historical biogeography of Papilionidae to identify the dispersal or vicariance events that best explain their present-day distribution, and test several proposed biogeographical hypotheses about the processes that shape distribution patterns in cosmopolitan groups. LOCATION World-wide, with disjunct elements. METHODS The phylogenetic relationships of 203 swallowtail species were determined by Bayesian inference using DNA data from mitochondrial (COI and COII) and nuclear (EF-1a) genes. Divergence time estimates were inferred using Bayesian relaxed clock approaches. To investigate competing biogeographical hypotheses, geographical range evolution was reconstructed using recently developed approaches: (1) a Bayesian empirical approach to dispersalvicariance analysis that takes phylogenetic uncertainty into account, and (2) a likelihood approach implementing the dispersalextinctioncladogenesis model that uses time-dependent stratified palaeogeographical matrices. RESULTS Our biogeographical results are congruent regardless of the biogeographical approaches or dating estimates used and support the importance of dispersal events in shaping swallowtail distributions. Contrary to common observations for other groups, the origins and diversification of northern taxa are better explained by range expansion through the Bering land bridge than by the Thulean or De Geer routes. We also stress that the seemingly Gondwanan biogeographical pattern in the Southern Hemisphere is more likely to have resulted from multiple, independent, long-distance dispersals than old vicariance events. The role of alternative colonization routes is also demonstrated for Madagascar, which facilitated multiple stepping-stone colonizations from India or Southeast Asia to Africa, and also for South America via the Caribbean land bridge. MAIN CONCLUSIONS Overall, the present geographical distributions of swallowtails can be better explained by dispersal events than by the long-held view of ancient vicariance events. This biogeographical study represents one of the most comprehensive phylogenetic and biogeographical studies on swallowtails. This work highlights the importance of using novel methodological approaches that provide the robust statistical frameworks needed to distinguish between competing biogeographical hypotheses. We emphasize the value of extensive taxonomic coverage for assessing the direction and frequency of supposedly rare events such as the multiple independent colonizations of Madagascar.