Meeting Abstract

S7-2.1  Sunday, Jan. 6  Egging each other on: embryonic communication in a nest maintains circadian rhythms of heart rate in turtles? LOUDON, FK; SPENCER, R-J*; University of Western Sydney, Australia

Amniotic eggs provide model organisms to explore the embryonic development of endogenous physiological circadian rhythms without the influence of maternal biorhythms. Recent studies have demonstrated that embryonic turtles within the nest respond to the developmental status of siblings by increasing both heart and metabolic rates, independent of temperature. A first step to understanding the physiological mechanisms underpinning this form of communication within a nest of ectothermic organisms is to develop profiles of embryonic heart rates at different temperatures throughout incubation. We developed daily embryonic heart rate profiles of embryonic freshwater turtles in different group sizes, under constant temperature and lighting conditions to determine if circadian rhythms exist and at what stage of embryogenesis they become established. Murray River turtle eggs were incubated in darkness at constant temperatures (26C and 30C) in groups of six or individually and heart rates were monitored at 6hr intervals over 24-48 hrs every seven days throughout incubation. Circadian heart rate rhythms were detected at week four of incubation and were maintained until hatching in on species. Heart rates throughout the day varied by up to 20% at constant temperatures over a 24h period and were not related to time of day. Circadian rhythms of heart rate were not as developed sympatric species that do not hatch synchronously. This study established that endogenous circadian rhythms of heart rate are established early during embryogenesis and suggests biotic cues from siblings within a nest (eg. changes in heart rate) may be as important as external environmental cues (eg. temperature) for establishing developmental rates and coordinating hatching and emergence from the nest.