Low Cost of Locomotion in Lizards That Are Active at Low Temperatures
16th Nov 2006, 09:50 GMT
The nocturnality hypothesis of K. Autumn and coworkers states that nocturnal geckos have evolved a low energetic cost of locomotion (C min). A low C min increases maximum aerobic speed and partially offsets the decrease in maximum oxygen consumption caused by activity at low nocturnal temperatures. We tested whether a low C min is unique to nocturnal geckos or represents a more general pattern of convergent evolution among lizards that enables nocturnality and/or cold-temperature activity. We measured C min in four carefully selected lizard species from New Zealand (two nocturnal and two diurnal; [FORMULA] individuals per species), including a nocturnal and diurnal gecko (a low C min is a gecko trait and is not related to nocturnality), a nocturnal skink (a low C min is related to being nocturnal), and a diurnal skink active at low temperatures (a low C min is related to being active at low body temperatures). The C min values of the four species measured in this study ([FORMULA] mL O2 g−1 km−1) are lower than those of diurnal lizards from elsewhere, and the values are within or below the 95% confidence limits previously published for nocturnal geckos. A low C min increases the range of locomotor speeds possible at low temperatures and provides an advantage for lizards active at these temperatures. We accepted the hypothesis that nocturnal lizards in general have a low C min and provide evidence for a low C min in lizards from cool-temperate environments. The low C min in lizards living at high latitudes may enable extension of their latitudinal range into otherwise thermally suboptimal habitats.
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