title: Is there more than one way to skin a newt? Convergent toxin resistance in snakes is not due to a common genetic mechanism.
abstract: Convergent evolution of tetrodotoxin (TTX) resistance, at both the phenotypic and genetic levels, characterizes coevolutionary arms races between amphibians and their snake predators around the world, and reveals remarkable predictability in the process of adaptation. Here we examine the repeatability of the evolution of TTX resistance in an undescribed predator-prey relationship between TTX-bearing Eastern Newts (Notophthalmus viridescens) and Eastern Hog-nosed Snakes (Heterodon platirhinos). We found that that local newts contain levels of TTX dangerous enough to dissuade most predators, and that Eastern Hog-nosed Snakes within newt range are highly resistant to TTX. In fact, these populations of Eastern Hog-nosed Snakes are so resistant to TTX that the potential for current reciprocal selection might be limited. Unlike all other cases of TTX resistance in vertebrates, H. platirhinos lacks the adaptive amino acid substitutions in the skeletal muscle sodium channel that reduce TTX binding, suggesting that physiological resistance in Eastern Hog-nosed Snakes is conferred by an alternate genetic mechanism. Thus, phenotypic convergence in this case is not due to parallel molecular evolution, indicating that there may be more than one way for this adaptation to arise, even among closely related species.
authors.affiliation: Department of Biology, University of Nevada Reno, Reno, NV, USA.
authors.forename: C R
authors.initials: CR
authors.lastname: Feldman
authors.affiliation: Department of Biology, Utah State University, Logan, UT, USA.
authors.forename: A M
authors.initials: AM
authors.lastname: Durso
authors.affiliation: Department of Biology, Utah State University, Logan, UT, USA.|Department of Biology, Utah State University, Uintah Basin, Vernal, UT, USA.
authors.forename: C T
authors.initials: CT
authors.lastname: Hanifin
authors.affiliation: Department of Biological Sciences, University of Notre Dame, Notre Dame, IN, USA.
authors.forename: M E
authors.initials: ME
authors.lastname: Pfrender
authors.affiliation: Department of Biological Sciences, State University of New York-Cortland, Cortland, NY, USA.
authors.forename: P K
authors.initials: PK
authors.lastname: Ducey
authors.affiliation: Department of Biology, California State University Bakersfield, Bakersfield, CA, USA.
authors.forename: A N
authors.initials: AN
authors.lastname: Stokes
authors.affiliation: New York State Department of Environmental Conservation, Albany, NY, USA.
authors.forename: K E
authors.initials: KE
authors.lastname: Barnett
authors.affiliation: Mountain Lake Biological Station and Department of Biology, University of Virginia, Charlottesville, VA, USA.
authors.forename: E D
authors.initials: ED
authors.lastname: Brodie
authors.affiliation: Department of Biology, Utah State University, Logan, UT, USA.
authors.forename: E D
authors.initials: ED
authors.lastname: Brodie
mesh_terms: D000220:Adaptation, Biological / Q000235:genetics; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000818:Animals; D005075:Biological Evolution; D017812:Colubridae / Q000235:genetics* / Q000502:physiology; D005838:Genotype; D008969:Molecular Sequence Data; D062553:NAV1.4 Voltage-Gated Sodium Channel / Q000235:genetics; D009518:New York; D010641:Phenotype; D011235:Predatory Behavior; D012455:Salamandridae; D013779:Tetrodotoxin; D014768:Virginia
chemical_list: D062553:NAV1.4 Voltage-Gated Sodium Channel; D013779:Tetrodotoxin