Thermal adaptations in lizard muscle function.

This study was undertaken to investigate thermal adaptations in muscle contractile properties in closely-related lizards with different preferred body temperatures (PBT). The species examined all belong to the Sphenomorphus group of Australian skinks (Scincidae: Lygosominae). Preferred body temperatures are conservative at the generic level as follows: Ctenotus, 35 degrees C; Sphenomorphus, 30 degrees C; Eremiascincus, 25 degrees C. Contractile properties of the fast glycolytic portion of the iliofibularis muscle were measured. Translational adaptations are evident in several isometric factors, including tetanic tension (Po), twitch tension (Pt), twitch time to peak tension (TPT), and twitch half-relaxation time (1/2 RT). Capacity adaptations are not evident in rates of tetanic tension development (dPo/dt) or in maximal velocities of isotonic shortening (Vmax). Rotational adaptations are not evident in any contractile properties. Thermal limits on upper response temperatures are about 5 degrees C warmer in Ctenotus than in the more cryophilic species, indicative of resistance adaptation in muscle performance. Despite these adaptive shifts, there is little indication that muscle functional capacities are optimized or equalized at PBT in these lizards.