Thermal strategies and energetics in two sympatric colubrid snakes with contrasted exposure

Abstract

The thermoregulatory strategy of reptiles should be optimal if ecological costs (predation risk and time devoted to thermoregulation) are minimized while physiological benefits (performance efficiency and energy gain) are maximized. However, depending on the exact shape of the cost and benefit curves, different thermoregulatory optima may exist, even between sympatric species. We studied thermoregulation in two coexisting colubrid snakes, the European whipsnake (Hierophis viridiflavus, Lacépède 1789) and the Aesculapian snake (Zamenis longissimus, Laurenti 1768) that diverge markedly in their exposure, but otherwise share major ecological and morphological traits. The exposed species (H. viridiflavus) selected higher body temperatures (approximately 30 degrees C) than the secretive species (Z. longissimus, approximately 25 degrees C) both in a laboratory thermal gradient and in the field. Moreover, this difference in body temperature was maintained under thermophilic physiological states such as digestion and molting. Physiological and locomotory performances were optimized at higher temperatures in H. viridiflavus compared to Z. longissimus, as predicted by the thermal coadaptation hypothesis. Metabolic and energetic measurements indicated that energy requirements are at least twice higher in H. viridiflavus than in Z. longissimus. The contrasted sets of coadapted traits between H. viridiflavus and Z. longissimus appear to be adaptive correlates of their exposure strategies.

Maternal influences on early development: preferred temperature prior to oviposition hastens embryogenesis and enhances offspring traits in the Children’s python, Antaresia childreni

“…The impact of chamber treatment on snake body temperature was first validated using physical models made from rubber tubes filled with water (Lelièvre et al, 2010), reproducing the thermal characteristics of the study species (correlation coefficient0.95).…”

Trophic niche overlap in two syntopic colubrid snakes (Hierophis viridiflavus and Zamenis longissimus) with contrasted lifestyles

“…Indeed, digestion duration is shorter in H. viridiflavus owing to its higher body temperature in the field. In a previous study (Lelièvre et al, 2010a), we found that transit duration at the preferred body temperature of each species was 2.75 ± 1.26 days in Z. longissimus vs. 1.50 ± 0.55 days in H. viridiflavus. Consequently, prey should remain detectable for almost twice as long in Z. longissimus.…”

“…These two species strongly differ in thermal adaptations (Lelièvre et al, 2010a) and thus provide a good opportunity to investigate the relationship between thermal strategy and dietary strategy. We documented a significant increase in the proportion of snakes captured with prey in the stomach, and in the total number of snake captures over the study period.…”

“…Z. longissimus shows strong morphological and behavioural similarities (constricting abilities, semi-arboreal, highly secretive) to ratsnakes (Naulleau, 1984;Burbrink and Lawson, 2007). These two species differ in their range of preferred body temperature (T set ): H. viridiflavus is thermophilic (T set 27.5-31 • C) whereas Z. longissimus prefers cooler temperature (T set 21.5-25.5 • C; Lelièvre et al, 2010a). We conducted our study at the Centre d'Études Biologiques de Chizé in Western France (46 • 07 N; 00 • 25 O).…”

“…These two species are appropriate models to examine the link between lifestyle and dietary habits because they are of similar size, but illustrate two distinct ecological orientations in snakes ("racer" versus "ratsnake"; see materials and methods for details on terminology). H. viridiflavus is a very active snake that selects higher body temperatures and exhibits higher energetic requirements than the elusive Z. longissimus (Lelièvre et al, 2010a(Lelièvre et al, , 2011. We expected that the difference in energy requirements should translate into dietary differences.…”