Who bites more: ecology of cannibalism in Salamandra salamandra

Fire salamander (Salamandra salamandra) generally uses slightly lentic epigean habitats as breeding sites. Nevertheless, where accessibility for adults is possible, deposition in hypogean environment is not infrequent. These sites are characterized by more constant environmental features, scarce availability of preys and nearly total absence of predators. Aim of this study has been to evaluate how provenience from such different environment populations and predator presence influence the typical intraspecific predation attitude of fire salamander larvae. For this purpose newborn larvae were collected from hypogean and epigean sites situated in an area within Como and Lecco districts (Lombardy, northern Italy). Subsequently collected individuals have been equally subdivided in three groups and exposed for a 45-day rearing period to three different predation risk conditions: predator absence; constant predator presence, but no direct contact; cyclical short-time exposition to predator with direct contact. The selected predator was a Cordulegaster bidentata larva, a dragonfly species commonly associated to S. salamandra epigean depositional sites, but almost absent in the hypogean environment. Under no circumstances predation has been permitted. In order to assess fire salamander larva aggressiveness ethological tests have been carried out, measuring the number of attacks performed by the focal individual to other non-treated newborn larvae (called ‘prey larvae’). Behavioural tests had been conducted before and after the rearing period. Moreover size differences between focal larvae and prey larvae have been taken into account. Results, obtained on the basis of linear mixed model statistical analysis, have shown a significant influence of larvae origin on their aggressiveness. In particular hypogean larvae exhibited a greater number of attacks towards prey larvae. On the other hand the number of cannibalistic interactions has not been affected by different rearing conditions, while it has been significantly positively influenced by size differences between focal and prey larva. These findings suggest that larval intraspecific predation in fire salamander is considerably affected by the habitat of origin and the size-structure of the population.