Do Toxin-Sequestering Snakes Recognize Their Own Nuchal Gland Toxin Reserve? Insights From Rhabdophis subminiatus

Abstract

Many animals with chemical defenses adjust their behavior depending on their toxin reserves. However, little is known about whether toxin-sequestering animals can directly monitor the amount of stored toxins. We investigated this question in the rednecked keelback (Rhabdophis subminiatus), which stores bufadienolides sequestered from toads in specialized integumentary organs called nuchal glands. We experimentally compared defensive behaviors before and after depletion of gland contents through mechanical extraction. Toxin depletion was confirmed by a significant reduction in both the mass and coloration of the extracted fluid. Across 23 individual snakes, no significant differences were observed in the frequency of defensive behaviors, including nuchal gland–related displays, between the full-toxin and toxin-depleted conditions. These results suggest that R. subminiatus does not directly recognize the current toxin reserve in its nuchal glands. Instead, toxin recognition in this genus may occur indirectly through factors related to feeding experience on toxin sources. Our findings provide new insight into the mechanisms and evolution of chemical defense regulation in toxin-sequestering snakes.