RAYMOND HUEY (MCZ) has introduced some new concepts into the study of 
lizard thermoregulation, a field dominated by the belief that careful 
thermoregulation is always beneficial, In particular he has stressed that 
behavioral thermoregulation has associated costs and that in consequence 
it is sometimes advantageous in terms of natural selection to be passive 
to environmental temperatures. 
He has demonstrated this point by studies on a population of Anolis 
cristatellus of Puerto Rico, some members of which live in shaded forest 
and some in a park-like area with scattered trees. He finds that indi- 
viduals in the open do indeed behaviorally thermoregulate, basking in the 
sun in the early and late parts of the day, while shifting to higher shaded 
perches at midday, These anoles maintain high and constant temperatures 
because access to radiant energy is very easy, almost cost-free., Their 
major behavioral reaction is to avoid extreme high temperatures by retreat 
to shaded situations, again an action with minimal energetic cost. 
In contrast, temperatures of animals in the forest were more variable 
and strongly correlated with air temperatures, reflecting the passive 
behavior of forest lizards, These animals would have had to move out of 
their territories to attain the few patches of sun. The energetic cost of 
such action is clearly great, suggesting that thermoregulation may yield 
greater net benefits than passivity only when associated costs are low. 
The same tolerance of low and variable temperatures was found by Huey 
and Webster in Anolis marmoratus of Guadeloupe (see details below). Huey 
and Slatkin are preparing a mathematical model of the cost-benefit relations 
involved in lizard thermoregulation. 
Huey also examined some physiological and behavioral parameters of 
thermoregulation in anoles of the cristatellus group of Puerto Rico. 
Previous work (Rand 1964, Heatwole et al, 1969, Huey and Webster in prep.) 
had shown that the three species form a partially overlapping altitudinal 
series, Where two forms are sympatric, the one with the higher altitudinal 
range invariably occurs in the more shaded habitats. Field work did not 
resolve whether these separations are presently the result of habitat 
exclusion or of thermal preference. To examine this question, Huey measured 
the experimental voluntary maximum temperature tolerated, critical thermal 
maximum, and preferred body temperature of the three species (Table 1). 
These results show that there are distinct behavioral and physiological 
differences among the three species, with gundlachi (high altitude) the 
least thermophilic and the most heat sensitive and cooki (arid lowlands) 
the most thermophilic and the least heat sensitive, These differences 
among sympatric pairs may in part account for habitat separations. 
