Climate warming and the agonistic behaviour of invasive crayfishes in E urope

Summary Climate warming often leads to shifts in the strength and sign of agonistic interactions among species, which in turn may change their distribution ranges. Notwithstanding the ubiquity of this phenomenon, there is scant literature about how interspecific agonistic behaviour changes with altered thermal regime, especially for invasive species such as three widespread N orth A merican crayfishes in E urope ( O rconectes limosus , P rocambarus clarkii and P acifastacus leniusculus ). We conducted a laboratory study to analyse some descriptors of agonistic behaviour in fighting dyads of similarly sized males of the three species' combinations, both at 20 °C (the current maximum water temperature in the study area, central F rance) and 27 °C (the maximum expected in the next 80 years under the more pessimistic IPCC greenhouse gas emission scenario). The results showed significantly different responses to warming by the three crayfishes. At 27 °C, O. limosus spent more time motionless and P . leniusculus was more often the subordinate, independent of the opponent. On the contrary, the agonistic strategy of P . clarkii did not change with temperature: when engaged in fighting, this species outcompeted both O . limosus and P . leniusculus . Caution should be taken when extrapolating laboratory studies to the field, but these results, combined with outputs of previous modelling exercises, suggest that European catchments will become dominated by P . clarkii with climate warming. Ultimately, this might lead to impoverished biodiversity, simplified food webs and altered ecosystem services.