Was the Ctenotus Adaptive Radiation Driven by Evolution of Thermoregulation?
Huey and Bennett (1987) and Garland et al. (1991) examined the influence of phylogeny on coadaptation of thermal physiology in some Australian skinks, including several species of Ctenotus. Their work, plus Greer’s (1980) comments, suggest that most, but not all, Ctenotus display appreciably higher body temperatures than related skinks. Apparently, acquisition of this “key innovation” (Simpson 1953, Futuyma 1986; Nitecki 1990) allowed Ctenotus to become active diurnal lizards and to radiate to fill many new niches. An alternative hypothesis is that aridification itself has allowed these lizards to diversify (see H 6). Huey and Slatkin (1976) analyzed costs and benefits of lizard thermoregulatory tactics, and identified the slope of the regression of body temperature against ambient environmental temperature as a useful inverse measure of the degree of passivity in regulation of body temperature. On such a plot of active body temperature versus ambient temperature, a slope of one indica
