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The oryzomyine rodent Euryzoryzomys russatus is endemic to the Atlantic Forest of South America, where it inhabits mostly pristine humid forests. Previous phylogeographical studies performed with limited sample sizes indicated that rivers and climatic oscillations might have driven the diversification of this species. Here, we used a more comprehensive database to revisit the phylogeography and demographic history of E. russatus. Our phylogenetic inferences and haplotype network recovered four groups within E. russatus , each of which diversified between 0.33 and 0.60 Mya. These groups are mostly allopatric and are structured latitudinally along the Atlantic Forest. We did not detect any genetic break related to the major river drainages. Species distribution models recovered similar suitable areas for E. russatus in the present and past times, suggesting stability in the geographical range during the Pleistocene. The most pronounced change was the expansion of suitable areas onto the emerged continental shelf during the Last Glacial Maximum. Demographic analyses showed evidence of population expansion during periods of lowered seal levels, especially for the haplogroup associated with the Serra do Mar forest refuge. Therefore, our results failed to support the hypothesis of riverine barriers and suggest that the diversification of E. russatus is explained better by forest refugial processes. [ABSTRACT FROM AUTHOR]

Opossums in the clade Didelphini are well known to be resistant to snake venom due to endogenous circulating inhibitors which target metalloproteinases and phospholipases. However, the mechanisms through which these opossums cope with a variety of other damaging venom proteins are unknown. A protein involved in blood clotting (von Willebrand Factor) has been found to have undergone rapid adaptive evolution in venom-resistant opossums. This protein is a known target for a subset of snake venom C-type lectins (CTLs), which bind it and then induce it to bind platelets, causing hemostatic disruption. Several amino acid changes in vWF unique to these opossums could explain their resistance; however, experimental evidence that these changes disrupt venom CTL binding was lacking. We used platelet aggregation assays to quantify resistance to a venom-induced platelet response in two species of venom-resistant opossums (Didelphis virginiana, Didelphis aurita), and one venom-sensitive opossum (Monodelphis domestica). We found that all three species have lost nearly all their aggregation response to the venom CTLs tested. Using washed platelet assays we showed that this loss of aggregation response is not due to inhibitors in the plasma, but rather to the failure of either vWF or platelets (or both) to respond to venom CTLs. These results demonstrate the potential adaptive function of a trait previously shown to be evolving under positive selection. Surprisingly, these findings also expand the list of potentially venom tolerant species to include Monodelphis domestica and suggest that an ecological relationship between opossums and vipers may be a broader driver of adaptive evolution across South American marsupials than previously thought., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

The geological record of South American mammals is spatially biased because productive fossil sites are concentrated at high latitudes. As a result, the history of mammalian diversification in Amazonia and other tropical biomes is largely unknown. Here we report diversification analyses based on a time-calibrated molecular phylogeny of opossums (Didelphidae), a species-rich clade of mostly tropical marsupials descended from a Late Oligocene common ancestor. Optimizations of habitat and geography on this phylogeny suggest that (1) basal didelphid lineages inhabited South American moist forests; (2) didelphids did not diversify in dry-forest habitats until the Late Miocene; and (3) most didelphid lineages did not enter North America until the Pliocene. We also summarize evidence for an Early- to Middle-Miocene mass extinction event, for which alternative causal explanations are discussed. To the best of our knowledge, this study provides the first published molecular-phylogenetic evidence for mass extinction in any animal clade, and it is the first time that evidence for such an event (in any plant or animal taxon) has been tested for statistical significance. Potentially falsifying observations that could help discriminate between the proposed alternative explanations for didelphid mass extinction may be obtainable from diversification analyses of other sympatric mammalian groups., (© 2013 The Author(s). Evolution © 2013 The Society for the Study of Evolution.)