Contemporary taxonomic work on New Caledonian Eumolpinae (Chrysomelidae) has revealed their high species richness in this Western Pacific biodiversity hotspot. To estimate total species richness in this community, we used rapid DNA-based biodiversity assessment tools, exploring mtDNA diversity and phylogenetic structure in a sample of 840 specimens across the main island. Concordance of morphospecies delimitation with units delimited by phenetic and phylogenetic algorithms revealed some 98-110 species in our sample, twice as many as currently described. Sample-based rarefaction curves and species estimators using these species counts doubled this figure (up to 210 species), a realistic estimate considering taxonomic coverage, local endemism, and characteristics of sampling design, amongst others. New Caledonia, compared with larger tropical islands, stands out as a hotspot for Eumolpinae biodiversity. Molecular dating using either chrysomelid specific rates or tree calibration using palaeogeographical data dated the root of the ingroup tree (not necessarily a monophyletic radiation) at 38.5Mya, implying colonizations after the Cretaceous breakage of Gondwana. Our data are compatible with the slowdown in diversification rates through time and are also consistent with recent faunal origins, possibly reflecting niche occupancy after an initial rapid diversification. Environmental factors (e.g. soil characteristics) seemingly played a role in this diversification process. © 2013 The Linnean Society of London.

This study was possible thanks to funds provided by the Committee for Research and Exploration of the National Geographic Society (grant no. 8380-07), and a travel grant from the Percy Sladen Memorial Fund of the Linnean Society. The work benefited also from the support of the Juan de la Cierva Programme (Spanish Ministry of Science, Technology and Innovation) to the first author, and the Fundación BBVA to the other authors. The Spanish National Institute for Bioinformatics and the IBE's IT team helped in the set-up for parallelization of processes. Fieldwork was carried out under the special authorization n° 6024-626 2008/DENV/SMT from the Direction de l'Environment (Noumea, New Caledonia) to our host in New Caledonia.

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