Selected Body Temperature and Thermoregulatory Behavior in the Sit-and-Wait Foraging Lizard Pseudocordylus melanotus melanotus

Abstract

We investigated the thermoregulatory abilities and behavior of Pseudocordylus melanotus melanotus (Drakensberg crag lizard) in terms of the relationship between the operative temperature (T e ), selected temperature (T sel ), set-point range (T set ) and field active body temperature (field T sel ), exposure to low temperature, body posture and activity. The T e range for P. m. melanotus was about 58 C (23.20 C in winter to 54.94 C in summer). In a laboratory thermal gradient, in a setting that is independent of ecological costs or thermal constraints, lizards maintained T set (defined as the interquartile range of T sel , after Hertz et al., 1993) between 29.00 6 0.36 C and 31.78 6 0.16 C in winter and 29.61 6 0.28 C and 32.47 6 0.18 C in summer. The mean T sel was 30.08 6 0.14 C in winter and 30.99 6 0.11 C in summer. In the field, however, lizards achieved significantly lower T b , which suggests that the thermal environment limited the T b that lizards were able to achieve. Lizards were active for significantly longer and selected significantly higher T b in summer than in winter. During winter, lizards spent a significant amount of time at T b below their lower critical limiting temperature (defined by loss of righting). The most frequently assumed body postures in summer were those where the head or body were raised, whereas, in winter, lizards usually lay with head and body flat on the rock substrate. We suggest that these differences reflect the physiological requirements of the lizards: Head-up postures in sit-and-wait foragers are consistent with scanning for prey while head-down postures are likely motivated by thermoregulatory needs. It is clear that P. m. melanotus can thermoregulate efficiently, but the T b maintained may be constrained by the range of T e available to the lizards in their natural environment. Pseudocordylus m. melanotus currently appears to be geographically constrained by low environmental temperatures at the edge of its range. Should global warming become a reality in southern Africa, this species could inadvertently benefit by occupying new habitat that was previously unavailable because of thermal constraints.

Feeding ecology of the common sun skink,Eutropis multifasciata(Reptilia: Squamata: Scincidae), in the plains of central Vietnam

“…For most reptile species inhabiting tropical regions, fewer animals are captured during the wet season compared to the dry season (Reilly et al 2007;McConnachie et al 2009;Vitt and Caldwell 2009). In this study, we collected relatively equal proportions in both dry (87 stomachs) and wet (74 stomachs) seasons, with a relatively equal proportion between the sexes (75 stomachs in females and 86 stomachs in males).…”

An evaluation of daily, seasonal and population-level variation in the thermal preference of a group-living lizard, Ouroborus cataphractus (Sauria: Cordylidae)

“…is more common (Patterson and Davies, 1978;Firth and Belan, 1998;McConnachie, Alexander and Whiting, 2009;Clusella-Trullas and Chown, 2014). Seasonal variation in Tp may counteract seasonal increases in thermoregulatory costs, since Tp may shift towards the prevalent envi ronmental temperatures (e.g.…”

“…Seasonal variation in Tp may counteract seasonal increases in thermoregulatory costs, since Tp may shift towards the prevalent envi ronmental temperatures (e.g. increase 7p dur ing summer) (Diaz and Cabezas-Diaz, 2004;McConnachie, Alexander and Whiting, 2009). Such shifts are facilitated through acclimati zation (reversible phenotypic/physiological plasticity) which alters the biochemical reac tion rates of temperature dependent processes, changing the optimum biological temperatures and hence Tp (Seebacher, 2005).…”

“…Few researchers have explored thermal pref erence in cordylids (Wheeler, 1986;Skin ner, 1991;Lailvaux, Alexander and Whiting, 2003;Clusella-Trullas et al, 2007;Janse van Rensburg, 2009;McConnachie, Alexander and Whiting, 2009). Recently Sinervo et al (2010), without referring to particular species, tabled the Tp of cordylids as 27.8°C-33.8°C (31.5 ± 0.82°C).…”

“…Recently Sinervo et al (2010), without referring to particular species, tabled the Tp of cordylids as 27.8°C-33.8°C (31.5 ± 0.82°C). Seasonal variation in Tp has been stud ied only in Pseudocordylus melanotus melanotus (McConnachie, Alexander and Whiting, 2009), and population level variation of 7p re mains unexplored for any cordylid. Clusella-Trullas et al (2007) reported that Tp estimates obtained for several cordylid species using laboratory thermal gradients that lacked retreat sites showed low individual repeatabil ity across experimental days (Clusella-Trullas et al, 2007).…”