In snakes, only children grow up to be loners

Communication between eggs is key to snake sociability after hatching.

Many reptiles start communicating with their siblings before they even hatch. New research into this behavior reveals that the practice can also affect behavior after hatching: viperine snake eggs incubated in isolation produced snakes that wanted nothing to do with their siblings. Lead author Fabien Aubret tells us more:

ResearchGate: What is embryo communication, and what information is communicated?

Fabien Aubret: Embryo-to-embryo communication can be described as an exchange of information between two or more developing embryos within a nest. It has been described in reptile eggs including birds—yes, birds are reptiles—snakes, lizards, and crocodiles. There is every possibility that such communication may also occur in other egg-laying species such as fish, crustaceans, and insects.

Embryo communication was first invoked as mechanism enabling hatching synchrony in turtles. In this case, the information conveyed relates to how fast the developing embryo is growing and when it is likely to hatch. This ensures they can hatch simultaneously. We know that synchronous hatching is important for small and fragile animals such as lizards, turtles, or snake hatchlings as it reduces their chances of being eaten by a predator—safety in numbers.

RG: How do embryos signal to each other from within the egg?

Aubret: Cues such as sound production, egg vibration, odors, or carbon dioxide levels within the nest have been proposed as potential communication avenues amongst embryos. In turtles and snakes we now know that embryos listen to each other’s heart rates, a very strong indicator of development rates and therefore a trustworthy clue about hatching date.

RG: What was this particular study designed to determine?

Aubret: In this study, we experimentally manipulated clutches of French water snakes (Natrix maura) to allow or prevent communication between embryos. To achieve this, we split clutches—groups of eggs laid at the same time—into two groups and placed them in incubators. One group was incubated as clusters where eggs were in physical contact with each other, the other with single eggs placed in individual goblets where eggs had no physical contact. By preventing physical contact and thus communication between eggs, we could observe the effects of rupturing the alleged bond between sibling eggs on the development rates of embryos, their size at birth, and also their post-natal social behavior.

RG: How did the behavior of the two groups of snakes differ after hatching?

Aubret: Single eggs produced less sociable young snakes than eggs that had been incubated as a cluster. We looked at the time young snakes spent close to their siblings when placed in a plastic box and realized that snakes that came from eggs incubated alone just wanted to leave and go somewhere else!  They were a lot more active and also avoided contacts with their mates. This was a surprising, yet fascinating outcome.

Snakes from egss incubated alone scattered after hatching, while those incubated together clustered.
Snakes from eggs incubated alone (left) scattered after hatching, while those incubated together (right) mostly clustered. Aubret et al. 2016.

RG: What is the significance of these findings?

Aubret: Communal nesting and clustering in egg-laying animals was known to offer a range of advantages; from anti-predatory benefits, maintenance of hydric balance, maintenance of egg positioning, to hatching synchrony. Our study suggested yet another driver for the evolution and maintenance of these reproductive strategies. Egg clustering, and incidentally embryo communication, may foster the establishment of “social bonds” amongst embryos.

RG: Why do you think this happens? How does it help the snakes?

Aubret: It’s a bit early be certain of benefits to individual snakes; but one can imagine that the creation and maintenance of social bonds amongst communally laid eggs may dilute the risks of predation and also provide thermal benefits to the offspring. Alternatively, embryo communication may allow developing embryos to assess the number of siblings within a clutch or communal nesting site. One may imagine that few or no neighboring eggs would be indicative of high predation levels on the eggs, or of a resource poor environment where females were only able to produce few eggs from which rapid dispersal is required. Conversely, a larger clutch may be indicative of relatively safer and resource full environment from which there is no direct advantage to disperse from, given that dispersing snakes are at high risks from predators.

RG: What’s next for this research?

Future studies are needed to address the evolutionary nature of these results, for instance by demonstrating the occurrence of similar single-child syndrome in other taxa, and by assessing the long-term effects of incubation circumstances on dispersal behavior, survival, and overall fitness.

Featured image courtesy of Pescalune Photo.