The imprints left by historical contingency on marsupials' life-history traits

Historical contingency may lead to distinct evolutionary imprints in early-isolated taxonomic groups. Here, we used comparative phylogenetics to unravel biogeographical imprints left by distinct historical contingencies on the evolutionary patterns of life-history traits of an iconic group, currently separated by ocean-wide distance: the marsupials. Australasian and New World marsupial communities share a common ancestry but were subjected to different biogeographic histories: while the Australasian community was effectively isolated from other faunas since disruption of land bridges with Antarctica, the evolution of New World marsupials was affected by the Great American Biotic Interchange. Contrary to our expectations, the exuberant diversity of life-history traits on Australasian marsupials did not exhibit evidence of early bursts of evolution, as expected on adaptive radiations. That surprising result is probably related to the assumptions of the ecological opportunities scenario - sensu Simpson (Tempo and mode in evolution, Columbia University Press, New York, 1994), which are hard to be met in continental scales. On the other hand, New World marsupials showed patterns of evolution consistent with niche conservatism, possibly due to the constraining effect of biotic interactions on niche evolution. Therefore, biotic interactions seem to have the limited evolution of New World life-history traits, whereas Australasian marsupials diverged into spectacular forms, though in a gradual and constant rate. The distinct biogeographic histories of the New World and Australasian marsupials thus provide a unifying explanation for the divergence patterns found in their life-history traits.