Abstract

Synchronous hatching occurs in many reptiles that lay multi-egg clutches, but this phenomenon and its potential environmental cues are poorly documented for species that lay their eggs singly, such as Anolis lizards. We tested for a circadian hatching rhythm in 196 Brown Anole (Anolis sagrei) eggs maintained in social isolation under a 12 : 12 L : D photoperiod with constant temperature and humidity. Hatching occurred exclusively in the morning and was approximately normally distributed around the transition from dark to light, with most (94%) eggs hatching ±1 hour from the onset of light. Hatching times differed significantly between sexes, such that most males hatched after the onset of light (71%), whereas only half of all females hatched after the onset of light (52%). That a substantial proportion of eggs (38% across sexes) hatched in the dark suggests circadian entrainment to photoperiod, rather than a direct behavioral response to light. Whether this reflects a natural circadian rhythm of hatching or an artifact of increased light exposure in our artificial incubation environment is presently unknown. If this circadian rhythm of hatching is a natural phenomenon, then its potential fitness benefits (e.g., optimal timing for predator avoidance, prey detection, water balance, or thermoregulation) warrant further attention.