Only child syndrome in snakes: Eggs incubated alone produce asocial individuals.

Egg-clustering and communal nesting behaviours provide advantages to offspring. Advantages range from anti-predatory benefits, maintenance of moisture and temperature levels within the nest, preventing the eggs from rolling, to enabling hatching synchrony through embryo communication. It was recently suggested that embryo communication may extend beyond development fine-tuning, and potentially convey information about the quality of the natal environment as well as provide an indication of forthcoming competition amongst siblings, conspecifics or even heterospecifics. Here we show that preventing embryos from communicating not only altered development rates but also strongly influenced post-natal social behaviour in snakes. Clutches of water snakes, Natrix maura, were split evenly into half-clutches and incubated as (1) clusters (i.e. eggs in physical contact with each other) or (2) as single eggs placed in individual goblets (i.e. no physical contact amongst sibling eggs). Single incubated eggs produced less-sociable young snakes than their siblings that were incubated in a cluster: the former were more active, less aggregated and physically contacted each other less often than the latter. Potential long-term effects and evolutionary drivers for this new example of informed dispersal are discussed.