Functional and physiological resistance of crayfish to amphibian toxins: tetrodotoxin resistance in the white river crayfish (Procambarus acutus)

Freshwater crayfish are reported to consume early life-history stages of a number of toxic amphibians. Although previous research indicates toxic amphibians are palatable to crayfish, the potential toxicity associated with consumption of toxic prey has been poorly described. We sought to characterise the supposed tetrodotoxin (TTX) resistance of freshwater crayfish, which have been observed to eat the eggs and larvae of toxic Taricha Gray, 1850 newts. White river crayfish (Procambarus acutus (Girard, 1852)) consumed 7.7 +/- 4.0 Rough-skinned Newt (Taricha granulosa (Skilton, 1849)) eggs (mean +/- SD) when offered 10 eggs in controlled feeding trials. Eggs were determined to contain a concentration of 1239 +/- 571 ng (mean +/- SD) of TTX. A dose-response assay was then performed to compare ingested doses with physiological TTX resistance. Crayfish were highly susceptible to TTX when administered as an intramuscular injection; TTX doses of 0.1 mass-adjusted mouse units were lethal to 100% of P. acutus crayfish. We established that while crayfish were capable consumers of highly toxic newt eggs, these decapods did not demonstrate physiological resistance to TTX. These findings suggest that crayfish have some functional resistance that renders them capable of consuming TTX-bearing prey despite a lack of physiological resistance to TTX.