Synchronous hatching is widespread among oviparous taxa. However, the adaptive significance of this phenomenon is unclear, as are the cues mediating hatching synchrony. We took a comparative approach and experimentally tested for synchronous hatching in two freshwater turtles with different life histories (Apalone spinifera and Graptemys geographica). We also aimed to disentangle the cues and mechanisms facilitating any synchronisation and explored its potential costs. For each species, we incubated eggs of different ages and from different mothers in two conditions—in direct contact with other eggs, or physically isolated but able to receive acoustic or chemical cues. We found evidence of hatching synchrony in A. spinifera, but not in G. geographica. Apalone spinifera eggs of different ages that developed in-contact hatched together, implicating mechanical cues. Younger eggs that were incubated in isolation also synchronised with in-contact eggs, which also implicates acoustic or chemosensory cues. Hatchling yolk sac size and mass were similar among treatments. Overall, A. spinifera exhibits hatching synchrony and there was no evidence of developmental costs. The lack of hatching synchrony in G. geographica may reflect their different life-history strategy, as this species can overwinter in the nest after hatching. Clutch effects explained a large and significant proportion of variance in both hatching date and incubation duration in both turtle species. Future research on hatching synchrony should control for these potentially confounding clutch effects. Variation in hatching or emergence synchrony among freshwater turtles raises questions about the selective forces that favour evolution of this behaviour.
Many freshwater turtles hatch from their eggs together—but how do they coordinate? We identified that if eggs of Spiny Softshell turtles develop in contact with each other, the eggs hatch together. But, Northern Map turtles do not synchronise hatching, possibly because of an important difference in their ecology—Northern Map turtles overwinter within their nest. Variable occurrence of hatching synchrony across turtle species may reflect different egg structures and/or overwintering behaviour. Research testing for the presence of hatching synchrony typically incubates less and more advanced siblings together. But we found that clutch effects explained a large and significant proportion of variance in both hatching date and incubation duration, which highlights the need to consider and control for these effects moving forward. Our study provides a promising experimental framework to study hatching synchrony that controls for clutch effects.
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We thank Anne and Ric MacArthur and the staff of Rondeau Provincial Park for logistical support during the project. Stephanie Chan, Rebecca Novack, Yehong Shi and Juliana Skuza assisted with care of the eggs during incubation. This study was supported in part by the Government of Ontario and Wildlife Preservation Canada. The initial manuscript was much improved by comments from Dr Sean Doody and an anonymous reviewer.
Collection of eggs for ex situ incubation was conducted for the recovery of the target population, and was funded by the Government of Ontario (Species at Risk Stewardship Fund grant SAR-00094) and by Wildlife Preservation Canada.
All applicable international, national and/or institutional guidelines for the use of animals were followed. This research was authorised under ESA Registry (M-102-4775033319), a Fish and Wildlife Scientific Collector’s Authorization, a Protected Areas Research Authorization, and an approved Animal Care Protocol (16-291) from the Government of Ontario.
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The authors declare they have no conflict of interest.
The datasets generated during and analysed in the current study are available in from Open Source Framework (OSF) at https://osf.io/mganf/.
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Riley, J.L., Hudson, S., Frenette-Ling, C. et al. All together now! Hatching synchrony in freshwater turtles. Behav Ecol Sociobiol 74, 58 (2020). https://doi.org/10.1007/s00265-020-2800-y
- Apalone spinifera
- Clutch effects
- Developmental plasticity
- Embryonic communication
- Graptemys geographica
- Parental effects