Insect Radiations on Islands: Biogeographic Pattern and Evolutionary Process in Hawaiian Insects

Abstract

The spectacular adaptive radiations on the Hawaiian Islands offer the tantalizing possibility of ascertaining the predictability of evolution, especially with regard to how the archipelago’s dynamic geology suggests a priori hypotheses for evolutionary pattern and process. In the past two decades advances in sequencing and phylogenetics have shed new light on the evolution of this model fauna. Here, we provide an overview of recent research on major endemic Hawaiian insect radiations. We find that, in contrast to earlier views, a substantial fraction of Hawaiian insect clades colonized the archipelago prior to the formation of the current high islands (5.1 Ma) and have persisted through one or more rounds of island formation and subsidence prior to the emergence of the current archipelago. Many Hawaiian insect radiations show elements of the progression rule, a null expectation where biogeographic patterns on the phylogeny mirror the chronological sequence of island formation, but few match its predictions exactly. Diversity in most radiations is shaped by a complicated interplay of among-island dispersal and within-island diversification. Finally, we find a positive relationship between clade age and species richness in Hawaiian insects, but with a great deal of variance that is likely explained by aspects of ecology and clade-specific factors.