Resistance of neonates and field-collected garter snakes (Thamnophis spp.) to tetrodotoxin

Prior studies of tetrodotoxin ( TTX) resistance in garter snakes ( Thamnophis spp.) have used laboratory-reared neonates as subjects, but the use of field-caught individuals would reduce cost and effort. We compared estimates of TTX resistance in field-caught and laboratory- born garter snakes. We found that a mass-adjusted dose of TTX administered to field-caught garter snakes produces an estimate of a population 50% dose that is comparable and unbiased with respect to those previously reported using laboratory- born neonates. Dose-response curves estimated for three field-caught populations closely matched the curves estimated from neonate data. The method was tested using populations with levels of TTX resistance ranging between approximately 5 - 90 mass-adjusted mouse units for their respective 50% doses. The technique of using field-caught snakes as test subjects provides larger genetically independent data sets that are more easily obtained. Our results indicate that changes in mass during development parallel ontogenetic shifts in TTX resistance.