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Keywords:

  • synchronous hatching;
  • turtle;
  • C. longicollis;
  • heart rate;
  • embryonic development;
  • egg

Abstract

Assessing environmental cues to coordinate birth or hatching has implications for both immediate and future survival. Predators may ultimately drive early or synchronous birth or hatching, because group formation allows neonate swamping of predators and reduces the impact of prey switching when large groups of neonates emerge from a nest. Turtles often emerge from the nest as a group, but temperature differences between the top and bottom of a nest are significant, making synchronous hatching difficult. The mechanisms of synchronous hatching in turtles are not consistent; with eggs hatching prematurely in one species, and another species displaying accelerated embryonic development, whereby embryos respond to the developmental rates of their siblings to hatch at similar developmental stages. If predation ultimately drives two disparate mechanisms of synchronous hatching, the physiological mechanisms behind synchronous, or early hatching, may be less developed in solitary nesting species, or species with smaller clutch sizes. I tested the hatching behavior of the Australian turtle, Chelodina longicollis, which has small clutch sizes and nests in isolation up to 1 km from water. I established developmental asynchrony within a clutch and used time to pipping to determine whether early or delayed hatching occurred. I also assessed heart rates throughout incubation to monitor changes in development. Synchronous or early hatching did not occur in C. longicollis and embryos did not adjust their rates of development in response to more or less advanced sibs within a clutch. Thus, environmental cues that are related to sibling developmental rates and hatching and which influence hatching times in other species do not affect embryonic development in C. longicollis. These results support the group formation theory for synchronous or early hatching in species that nest at communal areas, or species with large clutch sizes.