Diversity and diversification of New Caledonian Eumolpinae (Coleoptera: Chrysomelidae)

Abstract

New Caledonia is a biodiversity hotspot with exceptionally high species richness and endemism, resulting from a long history of isolation. Despite its appeal for evolutionary and biogeographic research, there is a very deficient taxonomic knowledge for most Neocaledonian organisms, particularly invertebrate groups, which hinders the general knowledge about evolution in this remote archipelago. In this study, we aim to assess species richness and diversification patterns of New Caledonian leaf beetles using a molecular phylogenetic approach and focusing on the worldwide distributed subfamily Eumolpinae, which currently comprises 59 described species endemic to New Caledonia. An extensive sampling was conducted in 57 localities across the main island and three additional samples were available from three surrounding islands. A total of 800 specimens were sorted to morphospecies and sequenced for two mitochondrial markers (cox1 and rrnS). DNA-based species delimitation was performed using the Generalised Mixed Yule-Coalescent model, which estimated 110 independently evolving entities, largely coinciding with morphospecies designation. Sample-based species accumulation curves indicated that sampling was far from complete. Incidence-based species estimators suggested that the expected total number of New Caledonian Eumolpinae could double the number of observed species, or quadruple the number of the currently described species. Molecular dating inferred a root age of 45-32 Mya, incompatible with a vicariant origin of this fauna in the Late Cretaceous fragmentation of Gondwana, but fitting the postulated re-emergence time of New Caledonia in the Oligocene following a period of island submersion. A significant slow-down in diversification rates through time, detected using the gamma statistic and model-based diversification analyses, also supports this scenario. In summary, our results support the recent origin of local endemics as proposed for other endemic insects and point towards a remarkable undiscovered diversity of New Caledonian Eumolpinae and the urgent need to increase our survey efforts.