Hatch or wait? A dilemma in reptilian incubation

Abstract

Animals often form groups to reduce the risk of predation through the per capita dilution of their individual predation risk. The advantages of grouping also influence the timing of reproduction in many species. In particular, synchrony in the timing of births may have evolved as a predator‐avoidance strategy as it dilutes the risk of predation upon vulnerable newborn and naive young. Eggs of an Australian freshwater turtle, Emydura macquarii, can hatch synchronously despite developmental asynchrony among eggs of a clutch and hatchlings have a reduced predation risk by emerging from the nest as a group. Developmental asynchrony within clutches was induced to reflect natural nests by dividing clutches and incubating them at either 25°C or 30°C. Some eggs were then reunited with their clutch‐mates and hatching occurred synchronously in some of these groups. In groups where synchronous hatching did not occur, less advanced eggs still hatched earlier than the normal incubation period. Synchrony occurred because the less advanced eggs hatched up to five days earlier than the control embryos. We conclude that the less advanced embryos within a clutch either accelerate their development or hatch prematurely to ensure synchrony of hatching and hatchling group formation may facilitate emergence from the nest and dilute predation risk.

Locusta migratoria (Orthoptera: Acrididae) embryos monitor neighboring eggs for hatching synchrony

“…Embryo-embryo communication within a clutch is known in vertebrates, including birds and reptiles (Colbert et al 2010, Doody 2011, Spencer et al 2001, Vergne and Mathevon 2008, Vince 1966. In snakes, developing embryos use heart beats emanating from neighboring eggs as a clue for their metabolic level, to synchronize development and ultimately hatching (Aubret et al 2016).…”

“…For embryo-embryo communication in vertebrates, cues such as sound production, egg vibration, increase in heart rates, odors, or carbon dioxide levels within the nest have been proposed as potential communication signals (Spencer et al 2001, Aubret et al 2016. In S. gregaria, synchronous hatching is observed when the eggs are incubated in a mass, but not when separated (Nishide and Tanaka 2016).…”

Synchronous activity lowers the energetic cost of nest escape for sea turtle hatchlings

“…Because all eggs within a clutch experience a similar incubation temperature, they hatch almost synchronously with their clutch mates, and at least some species are able to stimulate the hatching of clutch mates if the process has not already begun (Spencer et al, 2001). Synchronous hatching within a clutch results in incidental association among clutch mates and allows simultaneous digging activity of individual hatchlings.…”

Temperature-Dependent Sex Determination in Vertebrates

“…In some cases warm temperatures increase metabolic costs by an amount actually sufficient to retard growth (Porter and Tracy 1974). For example, O'Steen (1998) and Spencer et al (2001) found that cool-incubated turtles compensated by growing faster than warm-incubated turtles, and Rhen and Lang (1995) found that warm-incubated lizards grew more slowly. Letcher and Bengtson (1993) and Johnston et al (2001) report that fish given equivalent rations grow slower when maintained at warmer temperatures.…”