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Summary: Phylogenetic patterns of nocturnality and physiological capacity in
geckos. Kellar Autumn and Robert J. Full. Dept. of Integrative Biology,
Univ. of California, Berkeley 94720.
Nocturnal lizards provide an excellent model system in which to study
the effects of a substantial evolutionary shift in environment. Lizards are
ancestrally diurnal and the majority of lizard species, genera, and fami-
lies have remained diurnal. Nocturnality requires activity at body temper-
atures (Tb) 10-30ĄC lower than does diurnality. Because ectotherms are
profoundly affected by changes in body temperature, this is potentially a
major obstacle to nocturnal activity. Optimality theory predicts the coad-
aptation of thermal optima and activity temperatures. However, we have
shown that nocturnality imposes a thermal handicap which constrains
growth rate and endurance to submaximal levels. Physiologically, activ-
ity at low temperature reduces the maximal rate of oxygen consumption
( ), and therefore the maximum aerobic speed, which in turn reduc-
es endurance capacity. Frog-eyed geckos are active with an average Tb
of 15ĄC, yet have a thermal optimum for of 35ĄC. Data from sev-
eral gecko species shows that these nocturnal lizards have excellent fuel
economy (Cmin 1/2 to 1/3 that of phylogenetically comparable diurnal liz-
ards of similar mass) which partially offsets the thermal handicap. Yet,
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