River bank burrowing is innate in native and invasive signal crayfish (Pacifastacus leniusculus) and is driven by biotic and abiotic cues

The behavior of animals can change when they become invasive. Whilst many species demonstrate exaggerations of existing behaviors, signal crayfish (Pacifastacus leniusculus) display a novel burrowing activity in some invaded rivers. Understanding if burrowing is learned or innate is important for modelling the geomorphological effects of invasion into new territories. Mesocosm experiments were undertaken with signal crayfish to investigate the effects of population density, shelter availability, and population provenance on their likelihood to burrow. Crayfish were collected within their native range in the USA; a recently invaded site in the USA; and two well-established invasive populations in the UK-one where burrowing in the field was present, and one population where burrowing in the field was absent. Crayfish from all populations constructed burrows in laboratory experiments. Population density and shelter availability were significant drivers of burrowing. There was no difference in burrowing between the invasive UK populations and the US native population, suggesting that burrowing is an innate, rather than learned, behavior. Therefore, crayfish have the capacity to affect geomorphic processes in any river that they invade, regardless of the source population. However, crayfish from the recently invaded USA river excavated more sediment than crayfish from their native range. These results demonstrate high plasticity of signal crayfish activities and show that innate behavioral strategies not seen in the native range can be activated at invaded sites.