Incubation temperature and energy expenditure during development in loggerhead sea turtle embryos

Abstract

The choice of a suitable nest habitat by oviparous reptiles that deposit eggs into a nest and provide no subsequent parental care is likely to play a major role in the survival of the offspring. In particular variations in nest temperature may influence the rate at which embryos utilise their yolk energy. The effects of nest temperature on total energy use are however complex. High temperatures may advance development and shorten the time to hatching, thereby reducing energy use, but they also stimulate metabolic rate increasing energy use. The net effect of temperature on total energy demands is therefore uncertain. Oxygen consumption (VO 2) and carbon dioxide production (VCO 2) were measured by open-flow respirometry during the incubation of loggerhead sea turtle eggs at three temperatures (27.6, 30.0 and 31.8 °C). At each temperature, VO 2 and VCO 2 showed a peak followed by a decline to hatching. Incubation temperature was negatively related to incubation duration and positively related to the maximum metabolic rate of the embryos. Peak VO 2 was 74.8 ml/egg/day at 27.6 °C, 91.9 ml/egg/day at 30.0 °C, and 97.9 ml/egg/day at 31.8 °C. Peak VO 2 occurred closer to hatching in eggs incubated at higher temperatures. Total energy expenditure was greatest at the lowest incubation temperature and lowest at the highest temperature. Total VO 2 and VCO 2 were 1777 ml/egg and 1226 ml/egg, respectively, at 27.6 °C, 1680 ml/egg and 1235 ml/egg at 30.0 °C, and 1613 ml/egg and 1191 ml/egg at 31.8 °C. Using the actual RQ values, this corresponds to a cost of development of 34,963 J/egg at 27.6 °C, 33,403 J/egg at 30.0 °C, and 32,107 J/egg at 31.8 °C. At all temperatures, the calculated respiratory quotient values did not suggest that yolk substrates were oxidised proportionately, but more likely indicated their sequential use. Nest temperatures may play a key role in energy use, with cooler temperature nests increasing the overall energy demands placed on developing embryos.