Biogeography and evolution of widespread leafcutting ants, ata spp. (formicidae, attini)

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Solomon, Scott Even, 1979-

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Leafcutter ants (Atta spp.) are Neotropical herbivores that play important ecological roles, but are also notorious pests, causing millions of dollars in annual damage to agriculture across their range. Three species, A. cephalotes, A. sexdens, and A. laevigata, stand out as the most widespread and economically important. Two studies were conducted using these three species to better understand their biogeography and evolutionary history. First, using a maximum entropy niche-based modeling approach, locality information for these three species was used to (1) accurately describe the current geographic range of each species, (2) determine what factors limit their respective ranges, and (3) identify areas where each species is capable of becoming established. By comparing the model's predictions with published records and targeted surveys, a more accurate picture of the current ranges of each species was obtained. Areas in which a species does not currently occur, but that are predicted to be suitable, may reveal the ecological factors limiting the spread of these species. Such areas may also represent potential sites for invasion by these ants, with potentially devastating results. Second, these species were used to test the leading biogeographic hypotheses on the origins of high Amazonian diversity, an issue that remains unresolved despite much research. The hypotheses are the riverine barrier, Pleistocene refugia, and marine incursion hypotheses, each of which has been tested almost exclusively on vertebrates. A comparative, molecular phylogeographic approach was combined for the first time with paleodistribution modeling for the last glacial maximum to test these hypotheses on an insect. All analyses rejected the predictions of the riverine barrier hypothesis for each species. Tests of gene tree topology could not reject the refugia hypothesis for A. sexdens, while population-genetic and historical demography analyses failed to reject both the refugia and marine incursion hypotheses for all three species. However, coalescent-based estimates of population divergences for each species suggest that current population structure formed recently, suggesting that Miocene marine incursions have not promoted diversification in these species. Therefore, of the hypotheses examined, only the Pleistocene refugia hypothesis can explain the current population structure of Amazonian leafcutter ants.



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