Thermoregulatory behaviour of gravid and non‐gravid female grass snakes (Natrix natrix) in a thermally limiting high‐latitude environment

Abstract

All else being equal, ectotherms should maintain body temperatures (T b s) favourable for temperature-sensitive biological functions, such as digestion and locomotion. Physical environments in the temperate zone are often thermally variable, however, thus making it difficult to maintain optimum T b s. Radiotelemetry and a semi-natural enclosure were used to monitor T b s of grass snakes Natrix natrix at Canterbury, Kent, U.K. Operative temperatures (T e s) were measured using snake models (copper-pipe models) placed in a variety of microhabitats to determine availability of thermoregulatory opportunities. A modification of Huey & Slatkin's (1976) regression model, piecewise regression, was used to evaluate thermoregulatory behaviour. Grass snakes could achieve high mean T b s (> 30 • C) most often during midday (08:00-20:00), but only for 55-61% of the study period. Overall, non-gravid snakes maintained higher and less variable mean daytime T b s than gravid snakes. From piecewise regression, it was determined that grass snakes initiated thermoregulation at a T e of 38.44 • C, corresponding to a T b of 27.7 • C. Three main conclusions can be drawn from this study: (1) thermoregulatory opportunities for grass snakes were limited; (2) nonetheless, when conditions were sufficiently warm, there was clear evidence that grass snakes could thermoregulate; (3) contrary to expectation, gravid females actually maintained lower and more variable T b s than non-gravid females. The consequences of these thermoregulatory patterns for the fitness of snakes have yet to be determined.

Does gestation or feeding affect the body temperature of the golden lancehead, Bothrops insularis (Squamata: Viperidae) under field conditions?

“…Nonetheless, while this response holds for some snakes species (e.g. BROWN & WEATHERHEAD 2000, LADYMAN et al 2003 including tropical ones (LUISELLI & AKANI 2002, CHIARAVIGLIO 2006, it is absent in others (SANDERS & JACOB 1981, ISAAC & GREGORY 2004. For B. insularis we found that the T b of gravid females conformed to the general relationship between T b and T e , which indicates no change in thermoregulatory behaviour.…”

Sex, season, and time of day interact to affect body temperatures of the Giant Gartersnake

“…It would therefore be informative to examine intersexual differences in T b in March and April to further examine this hypothesis. In a similar manner, normal embryonic development is dependent on temperature (Lillywhite, 1987), and females may thermoregulate to achieve high T b to aid embryonic development during the summer gestation period (Charland, 1995;Gregory et al, 1999;Isaac and Gregory, 2004;Kapfer et al, 2008). Thermoregulatory behavior has a strong influence on the duration of gestation and fitness of offspring in viviparous squamates (Shine and Harlow, 1993;Lourdais et al, 2004); therefore, natural selection may act upon females to thermoregulate precisely while gravid (Shine and Harlow, 1993).…”

“…For example, maternal temperature during different stages of development affects the number of body segments, developmental rate, and the incidence of stillbirths in the Aspic Viper (Vipera aspis; Lourdais et al, 2004). If thermoregulation to high T b has associated costs, such as increased predation risk (Huey and Slatkin, 1976;Peterson, 1987;Charland, 1995;Isaac and Gregory, 2004), reduced T b may be an adaptive response when fitness benefits of reproductive activity are not imperative. Alternatively, differing T b may be a consequence of differences in behavior, rather than causing differences in behavior.…”

Thermal Biology of Reproduction in Female Eastern Foxsnakes (Elaphe gloydi)

“…Whereas changes in thermoregulatory behavior attributable to reproductive condition have been well documented for viviparous snake species (e.g., Graves and Duvall, 1993;Charland, 1995;Dorcas and Peterson, 1998;Brown and Weatherhead, 2000), the subject has been investigated to a lesser extent in oviparous taxa (e.g., Blouin-Demers and Weatherhead, 2001a;Isaac and Gregory, 2004). This disparity is due at least partly to the relatively shorter period of egg retention in oviparous species, with the consequent effect of making changes in thermoregulatory behavior (e.g., increased basking) less amenable to casual observation or quantification.…”