Joint estimation of divergence time and trait evolution in a newly delineated island species flock

Rapid adaptive radiations are generally thought to occur soon after a lineage invades a region offering high levels of ecological opportunity. However, more examples of adaptive radiation are needed if we wish to comprehensively understand their dynamics outside of a handful of exceptional examples. Here, we present a novel case of an island species flock of freshwater fishes with a radically different tempo of adaptation history compared to many popular evolutionary model systems. Using a highly resolved phylogenomic dataset combined with simultaneous Bayesian estimation of divergence times and trait-based speciation and extinction models, we show that the New Zealand Gobiomorphus gudgeons comprise a monophyletic assemblage, but surprisingly, the radiation did not fully occupy freshwater habitats and explosively speciate until more than ten million years after the lineage invaded the islands. Our results challenge the notion that clades always rapidly exploit ecological opportunities in the absence of competing lineages.