Does Prey Matter? Geographic Variation in Antipredator Responses of Hatchlings of a Japanese Natricine Snake (Rhabdophis Tigrinus)

Rhabdophis tigrinus, which typically forages on toads, has unusual nuchal glands on its dorsal neck region containing secretions chemically comparable to cardiac steroids found in toads. R. tigrinus also has several peculiar antipredator displays involving the neck region. If the nuchal gland secretions of R. tigrinus are derived from toads obtained as prey, populations of R. tigrinus that have not eaten toads over an evolutionary time scale would be expected to lose antipredator displays related to the nuchal glands. We found that laboratory-hatched R. tigrinus from a small toad-free island exhibited displays related to nuchal glands less frequently and flight responses more frequently than hatchling snakes from areas sympatric with toads. These results are consistent with the hypothesis of the dietary origin of the nuchal gland secretions and also support the genetic origin of the behavioral differences between the populations.