Temperature Effects on Anti‐Predator Behaviour in Rhabdophis tigrinus, a Snake with Toxic Nuchal Glands

Abstract

Many contextual factors affect the anti‐predator behaviour of animals. In ectotherms, in which most physiological activities depend on body temperature, ambient temperature is one of the most important of these factors. We examined the effects of temperature on the anti‐predator behaviour of an ectotherm, the Japanese grass snake (Rhabdophis tigrinus). This species has a large repertoire of anti‐predator behavioural responses. Among these responses are several anti‐predator displays that appear to be unique to this species and perhaps others in a small group of closely related species possessing nuchal glands containing toxic secretions that may be derived from their toxic toad diet. Snakes were tested at room temperatures of 14, 22 and 30°C with order of temperatures balanced. A long wand modified to simulate initial contact by a predator was used as the stimulus. Snakes exhibited rather passive responses (neck flatten, body flatten, neck arch and immobile) more frequently at low temperatures, and fled more frequently at high temperatures. The dorsal facing posture, a characteristic posture directed against the stimulus, was observed more frequently at low temperatures. Threatening, assertive responses such as strike were rarely observed. These results showed that R. tigrinus shifts its anti‐predator behaviour from multiple passive responses to active flight responses with increasing temperature. This snake species thus appears to rely more on its nuchal glands as a predator deterrent at low ambient temperatures. Consistent individual variation was also observed, and its adaptive and causal bases are discussed.

Young fire ant workers feign death and survive aggressive neighbors

“…Variation in the initiation and duration of anti-predatory death feigning is correlated with environmental factors such as temperature, threat type, and threat intensity, as well as demographic factors such as age, sex, reproductive state, and feeding history (Holmes 1906;Acheampong and Mitchell 1997;Mori and Burghardt 2001;King and Leaich 2006). In some cases, variation in the duration of feigning death is heritable and adaptive (Sazima 1974;Sargent and Eberhardt 1975;Prohammer and Wade 1981;Arduino and Gould 1984;Miyatake et al 2004;Honma et al 2006;Ohno and Miyatake 2007).…”

Comparative experimental tests of natricine antipredator displays, with special reference to the apparently unique displays in the Asian genus, Rhabdophis

“…Another ophidian antipredator behavior that may be associated with a unique morphological feature is a suite of responses, including arching of the neck and butting with the neck, observed only for the Asian natricine snake, Rhabdophis tigrinus tigrinus (Fukada 1961;Mutoh 1983;Mori et al 1996; Burghardt 2000, 2001). These responses seem to be associated with the presence of unusual organs called nuchal glands (Fukada 1961;Mori et al 1996;Mori and Burghardt 2001), a series of paired glands embedded under the dorsal skin of the neck region (Nakamura 1935;Smith 1938). The glands, which are ontogenetically of mesodermal origin (Fukada 1958), have no duct, but the skin covering the glands is relatively thin and easily broken under pressure, causing release of the secretion.…”

“…Because factors such as temperature, type of stimulus, and method of testing can affect the antipredator responses of snakes, however (Burghardt and Schwartz 1999), negative evidence must be carefully evaluated. Previous studies of R. tigrinus demonstrated that physical contact on the neck region is the most effective stimulus for eliciting the above displays (Mori et al 1996;Mori and Burghardt 2001), but this type of stimulus has not been typically used in experiments on other natricine snakes. To confirm the absence or presence of this behavior in snakes, we therefore used a standardized experimental method in a diverse sample of Old World and New World species that do not have the nuchal glands.…”

Thermoregulation is the pits: use of thermal radiation for retreat site selection by rattlesnakes

“…Gvozdik, 2002), and predator avoidance (e.g. Mori and Burghardt, 2001). The ability to locate favorable microsites efficiently minimizes these constraints while maximizing time spent at optimal body temperatures (Huey, 1991).…”