Concerted versus independent evolution and the search for multiple refugia: comparative phylogeography of four forest beetles

Phylogeographic structure and its underlying causes are not necessarily shared among community members, with important implications for using individual organisms as indicators for ecosystem evolution, such as the identification of forest refugia. We used mitochondrial DNA (cox1), Bayesian coalescent ancestral state reconstruction (implemented in BEAST), and ecological niche models (ENMs) to construct geospatial histories for four codistributed New Zealand forest beetles (Leiodidae, Nitidulidae, Staphylinidae, and Zopheridae) to examine the extent to which they have tracked environmental changes together through time. Hindcast ENMs identified potential forest refugia during the Last Glacial Maximum, whereas ancestral state reconstruction identified key geographic connections for each species, facilitating direct comparison of dispersal patterns supported by the data and the time frame in which they occurred. Well-supported geographic state transitions for each species were mostly between neighboring regions, favoring a historical scenario of stepping stone colonization of newly suitable habitat rather than long distance dispersal. No geographic state transitions were shared by all four species, but three shared multiple projected South Island refugia and recent dispersal from the southernmost refugium. In contrast, strongly supported dispersal patterns in the refugia-rich northern South Island suggest more individualistic responses to environmental change in these ecologically similar forest species.