Origins of old lineages in New Caledonia: A geologically informed test of the island-hopping hypothesis

Aim: Although New Caledonia (NC) is now considered an oceanic island that emerged ca. 60 Ma, a few terrestrial clades are significantly older, raising the question of the origin of these groups. Classically, old lineages on more recent islands are hypothesized to originate through a process of hopping on now-vanished islands (i.e., island-hopping hypothesis) or other territories. We aim to test this hypothesis by studying a group of cockroaches with several lineages found in NC. Location: New Caledonia, New Zealand, Australia. Taxon: Insects: Blattodea. Methods: We generated a dated phylogeny for blattid cockroaches (Blattidae and Tryonicidae) using Bayesian inference along with fossil calibrations. We reviewed studies on the palaeogeography of the Southwest Pacific region, including hypotheses about the existence of yet-to-be-discovered past islands, and constructed biogeographical tests accordingly. We computed ancestral area estimation under different models in BioGeoBEARS (DEC, BAYAREALIKE, DIVALIKE, with or without +J) to test the role of an island-hopping hypothesis in the establishment of NC blattid fauna. Results: We find divergence times older than 60 Ma for two NC clades. We show that these 'old' endemic lineages can partially be explained by indirect dispersal from Australia or New Zealand through now disappeared islands. Alternative hypotheses suggest multiple independent colonizations of NC from Antarctica or Australia. Main Conclusions: Our results indicate that island-hopping may explain the presence of old groups in NC. The island-hopping hypothesis is nonetheless only supported for a period-area from which geological evidence is ambiguous. Our work highlights both the fruitful interactions between geology and biogeography and the underlying difficulties. The multiple colonization events inferred for NC provide additional insights into the composite nature of NC biota.