Does nocturnal activity prolong gecko longevity?

Abstract

The majority of lizard clades are ancestrally and predominantly diurnal. The only major taxon in which most species are nocturnal is the Gekkota (geckos and pygopodids). As ectothermic thermoregulators, lizard metabolic rates are highly temperature dependent, and diurnal lizards therefore demonstrate higher metabolic rates than nocturnal ones. Furthermore, exposure to solar radiation is thought to reduce ectothermic longevity by increasing both metabolic costs and the rate of accumulating harmful mutations through UV radiation (UVC specifically). In being nocturnal, ectothermic species may reduce their intrinsic mortality rates and thus live longer. To test this hypothesis, we collected literature data on the maximum longevities of 740 lizard species, of which 185 are geckos. We examined whether geckos live longer than other lizards, and whether activity time affects gecko longevity. While geckos live relatively long for lizards of their size, their activity time was found to be unrelated to longevity, contradicting our predictions. We suggest that diurnal species may have evolved higher resistance to UV radiation via thicker, more keratinized skin. Elevated metabolic rates do not automatically equate with faster aging. Mortality through extrinsic causes (e.g., predation) may impose much stronger selective pressures than intrinsic causes.