Research
Coevolution is a phenomenon that has been central to evolutionary biology since its beginnings, when biologists and naturalists began to recognize that patterns of adaptation and counter adaptation produce reciprocal changes in phenotype akin to an arms race. The best studied examples of these arms races include obligate mutualisms, host-pathogen models, and predator prey systems. However, the difficulty in demonstrating a truly reciprocally evolving interaction distinct from plastic or pre-adapted interactions has been problematic since the birth of the field. Only recently has it become possible to characterize coevolution at the molecular level, where changes in one protein affect changes in other, interacting proteins. Still, while new research has revealed important insights, empirical examples of molecular coevolution remain scarce, and this process has yet to be characterized by reciprocal functional and molecular changes in both interacting partners. This leaves a significant chasm in our understanding of the molecular basis of coevolutionary interactions, and how observed molecular changes translate into functional shifts in the co-adaptive landscape. Much of my work focuses on elucidating whether systems which appear to be coevolving at the macroscopic scale are truly exhibiting reciprocal molecular and functional change, and further discerning the tempo and mode of that change.
Bothrops jararaca. Photo by Márcio Cabral de Moura
http://tinyurl.com/q65ckmj
Opossums and Vipers
Members of the South American marsupial family Didelphidae are not only resistant to snake venom but also attack and eat pit-vipers with impunity, exhibiting no behavioral precautions while subduing these dangerous snakes. In particular, several members of this tribe are known to prey upon Bothrops jararaca, a South American pit viper. Bothrops jararaca venom is known to contain a C-type-lectin (CTL) protein, Botrocetin, which specifically targets vWF (von Willebrand factor), and causes excessive systemic bleeding. Resistant opossums combat many types of venom proteins with proteinase inhibitors, but they also show accelerated evolution at the vWF- botrocetin binding site (vWF A1 subunit) when compared to non-resistant species (Jansa and Voss 2011).This is potentially an adaptive response to botrocetin, and may prevent Botrocetin from being active against these species.
Didelphis virginiana
photo by Gary Owens http://tinyurl.com/puvp9ac
I am currently running physiological and biochemical assays to understand the potential coevolutionary relationship between Didelphids and their venomous prey, by focusing on the interaction between vWF and Botrocetin-type venom components. Utilizing a wide breadth of techniques from molecular biology to biophysics, I aim to understand how these proteins interact, and how coevolution might have shaped their physiological and kinetic properties.
I am also using phylogenetic tools to reconstruct ancestral proteins states of vWF and Botrocetin-like venom proteins. Using modern techniques, it is now possible not only to examine ancestral sequences in silica, but also to express these proteins in vitro and test their biochemical and physiological functions as they once existed.
Photo credit: Fort Wayne Children's Zoo
Honey Badgers and Cobras
The Honey Badger (Mellivora capensis) is an African mustelid which is also known to regularly prey upon venomous snakes, in particular, the Cape Cobra. These snake are known to contain venom with potent neurotoxins, called alpha-neurotoxins. The muscular nicotinic acytlecholine receptor (nACHr) is targeted by these alpha-neurotoxins. Some mammals have evolved venom-resistant nAChRs that no longer bind these toxins. Using a comparative phylogenetic analysis of mammalian nAChR sequences, we found that honey badgers, hedgehogs, and pigs have independently acquired functionally equivalent amino acid replacements in the toxin-binding site of this receptor. In venom-resistant mongooses, different replacements are present at these same sites but prevent toxin binding through a different mechanism. I am interested in understanding the ecological drivers of convergence events such as this. I am also interested in understanding the gross physiological consequences of these adaptive changes, as well as the influence of constraint upon these adaptive changes.
The Honey Badger (Mellivora capensis) is an African mustelid which is also known to regularly prey upon venomous snakes, in particular, the Cape Cobra. These snake are known to contain venom with potent neurotoxins, called alpha-neurotoxins. The muscular nicotinic acytlecholine receptor (nACHr) is targeted by these alpha-neurotoxins. Some mammals have evolved venom-resistant nAChRs that no longer bind these toxins. Using a comparative phylogenetic analysis of mammalian nAChR sequences, we found that honey badgers, hedgehogs, and pigs have independently acquired functionally equivalent amino acid replacements in the toxin-binding site of this receptor. In venom-resistant mongooses, different replacements are present at these same sites but prevent toxin binding through a different mechanism. I am interested in understanding the ecological drivers of convergence events such as this. I am also interested in understanding the gross physiological consequences of these adaptive changes, as well as the influence of constraint upon these adaptive changes.