Effects of Body Size and Condition on Antipredator Behavior Related to Nuchal Glands in Rhabdophis subminiatus

Abstract. Snakes have a wide range of antipredator behaviors that are often associated with unique morphological modification. Rhabdophis subminiatus (Red-Neck Keelback) is a snake with nuchal glands where toxins sequestered from prey animals are stored that work in conjunction with a set of antipredator behaviors. In this study, we investigated antipredator behavior in this species, particularly behavior that is coordinated with the presence of the nuchal glands. We tested the hypothesis that the nuchal gland-related behavior is exhibited more frequently as snake size increases because larger snakes have had more opportunities to consume toads and acquire toxins. We also examined the effects of sex and body condition on antipredator behavior. All snakes performed body flattening and neck flattening in response to a standardized stimulus, which suggests that these responses are their major antipredator behaviors. However, the results did not support our hypothesis. Snake body size was negatively correlated with the frequency of neck butt, neck flatten, and neck arch. This indicates that the tendency to perform the nuchal gland-related behavior declines as body size increases. There was no significant sexual difference except that females tended to exhibit a higher frequency of flight than males. Furthermore, we found a negative correlation between the frequency of neck butt and body condition. Overall, our study suggests that smaller snakes, particularly those in below-average body condition, depend more on nuchal glands to deter predators.