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Revisiting the Great American Biotic Interchange through analyses of amphitropical bees



The Great American Biotic Interchange (GABI) is zoogeographic event characterized by the exchange of taxa between North and South America, typically associated with the rise of the Isthmus of Panama in the late Pliocene. Recent geologic evidence suggests the connections between North and South America may be much older, and that the interchange of organisms between the two continents could have therefore happened much earlier than 3 Ma. Most of the research investigating the GABI has come from tropical vertebrate taxa; little work has been done on invertebrates or on non-tropical species. To investigate how the GABI shaped the distribution of arid-adapted species, particularly those with amphitropical distributions (i.e. taxa found in South and North American xeric regions yet absent from the tropics), we examine the historical biogeography of the bee genus Diadasia using a hypothesis of Diadasia phylogenetic relationships. Nuclear and mitochondrial genetic loci are used to reconstruct a phylogeny of Diadasia, which is then used to estimate divergence dates and reconstruct ancestral area relationships. Our analyses suggest the divergence between North and South American Diadasia species occurred between 20.5 and 15 Ma, long before the formation of the Isthmus of Panama. This study is the first to show a Miocene connection for an amphitropically-distributed insect group. It suggests that the biotic connection between continents is more complicated than previously thought and may have initiated long before the late Pliocene.