Life cycle and behavioural traits of Dikerogammarus villosus (Sowinsky, 1894) (Amphipoda, Gammaridae) colonising an artificial fresh water basin in Tuscany (central Italy)

The water amphipod Dikerogammarus villosus (Sowinsky, 1894) has colonised many rivers and water basins in central Europe and is rapidly reaching southern Europe. It was found in northern Italy in 2006 and in central Italy in 2008. In this last area it has colonised the recent artificial basin of Bilancino (Mugello Valley, Florence), currently being the only and abundant amphipod species in the lake. This new population offered a good opportunity to study the life cycle and behaviour of such unpopular species (called killer shrimp because of its aggression), with the aim of better understanding the mechanisms of survival and diffusion of water gammarids. For about one year and a half, bimonthly samplings were carried out in different points of the lake to study the life cycle and identify the most suitable populations for behavioural experiments. On this species experiments were carried out in the natural context to verify sun and landscape orientation and in the laboratory to analyse the response to a black boundary, direct light and substrate slope. The populations from the different points had a comparable structure and development, even if subjected to variations linked to the local features of the lake’s bottom. The response to the black boundary (simulating a predator or a refuge) was not significant, while a significant reaction of avoidance of a direct artificial light and a significant preference for the basin bottom (downslope) were observed. No specific responses were identified where the behaviour was strictly linked to the environment colonised (orientation to the sun and natural landscape). A lack of fine-tuned adaptations was expected in this species that has colonised a variety of environments, confirming comparable results on the physiology of this species, such as adaptation to wide ranges of temperature, salinity and oxygen levels.