Hatchling vocalizations and beneficial social interactions in subterranean nests of a widespread reptile

Signals are fundamental to communication, and theory suggests signals may evolve to coordinate cooperation on complex tasks. Several recent studies have demonstrated that hatchling turtles vocalize within the subterranean nest cavity, and these vocalizations are hypothesized to promote hatching synchrony and coordinate emergence from subterranean nests (social facilitation hypothesis). Here we test assumptions and predictions of the social facilitation hypothesis in the snapping turtle, Chelydra serpentina, a species with a broad distribution. First, we demonstrate that C. serpentina hatchlings have a vocal repertoire: we identified six types of vocalizations in a simulated nest environment, with one vocalization type occurring before egg pipping and all six types occurring in the 24 h following egg pipping and hatching. We found that Simpson's diversity was greater for vocalizations during the hatching stage compared to the emergence stage and was minimal during the prepipping stage. Second, we manipulated egg burial depth (shallow or deep) and sociality (presence or absence of siblings) in a 2 x 2 factorial design. We found that eggs in the social treatment hatched earlier and lost less mass while emerging from the nest, underlining a likely energetic benefit to hatchlings emerging with siblings versus emerging alone. Third, we tested a subhypothesis of the social facilitation hypothesis, which is that embryos cue hatching in response to hatchling vocalizations. However, vocalization playback to late-stage (prepipping) embryos did not alter pipping date relative to controls. Our combined results provide some support for the social facilitation hypothesis: there are likely energetic benefits to group emer-gence, embryos in a group hatch earlier, but earlier group hatching is not cued by vocalizations per se. Our study contributes to a growing literature on the adaptive significance of sociality in reptiles and helps disentangle the proximate drivers of vocalizations in hatchling turtles. (c) 2022 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.

Automated summary

Signals are important for communication in animals, and recent studies have shown that hatchling turtles vocalize to coordinate hatching and emergence. This study investigated the social facilitation hypothesis in snapping turtles and found evidence supporting the hypothesis. Hatchlings exhibited a vocal repertoire, and group emergence resulted in earlier hatching and reduced mass loss. However, vocalizations did not directly cue group hatching. This study contributes to the understanding of sociality in reptiles and the proximate factors driving vocalizations in hatchling turtles.