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.
Bibliographical noteFunding Information:
Funding for this work was provided by the Rosemary Grant Award from the Society for the Study of Evolution, and the UMN Ecology, Evolution, and Behavior Department Travel Grant. Funding was also provided by the American Society of Mammalogists Grant in Aid, and the American Society for Ichthyologists and Herpetologists Gaige Fund Award. EHZ was financed by Biota FAPESP grant #2016/50127-5. Permission for opossum trapping was granted by the State of Minnesota Department of Natural Resources (permit No 16312). This research was conducted in accordance with University of Minnesota's Institutional Animal Care and Use Committee (IACUC # 1303?30464 A), and Instituto Butantan's Comit? de ?tica em Experimenta??o Animal (CEUAIBu) (protocol #8346081018). Special thanks to Miguel Cruz for reagents and invaluable lab mentorship. Thanks to Kristen Wiley at the Kentucky Reptile Zoo, Nicole Zantec and Dan Keyler at UMN for generously sharing reagents and advice. Thanks to the undergraduate and graduate researchers in the Hingst-Zaher Lab at Instituto Butantan with special thanks to Fernanda Pricolli for help in trapping and testing in Brazil. We would like to especially thank Kalena Barros and Silvia Travaglia for their help. We are grateful for the revisions, editing, and advise from Dr. Keith barker and Dr. Georgiana May that were invaluable to this work. We would also like to thank two anonymous reviewers for their careful reading of this manuscript, and for their suggestions which have substantially improved the clarity and presentation of this work.
© 2020 Elsevier Ltd
- C-type lectins
- Platelet aggregation
- Venom resistance