Lemurs are celebrated as a textbook example of adaptive radiation. Since colonizing Madagascar, more than 100 lemur species have evolved to fill a wide variety of ecological niches on the island. However, recent work suggests that lemurs do not exhibit one of the classic hallmarks of adaptive radiations: explosive speciation rates that decline over time. Here, we explore this idea using a phylogenomic dataset with broad taxonomic sampling of strepsirrhine primates (lemurs and their neglected sister group, the lorisiforms of Asia and continental Africa). We find higher rates of speciation in lemurs compared to lorisiforms, and while we confirm that lemurs did not experience an early burst of speciation after colonizing Madagascar, we surprisingly identify three independent bursts of speciation approximately 15 million years ago that underly much of lemur diversity. We demonstrate that the lemur clades with exceptionally high diversification rates are correlated with higher rates of gene flow. In light of the extinction crisis currently facing strepsirrhine primates, with approximately 95 percent of species being threatened with extinction, this phylogenomic study offers a new explanation for the exceptional primate diversity of Madagascar and reveals patterns of speciation, extinction, and gene flow that will be important for conservation decisions going forward.
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