The aggressive personality of an introduced fish affects foraging behavior in a polymorphic newt

The study of personality has aroused much interest and has provided insight into the understanding of animal behavior. Nevertheless, the study of the ecological consequences of personality is a newer field that could shed light on cases of alien species introductions. The goldfish (Carassius auratus) is frequently introduced worldwide and affects the abundance of newts, having an especially negative impact on an alternative phenotype, the paedomorph, which maintains larval traits at the adult stage, unlike the other phenotype, the metamorph, which has undergone metamorphosis. We experimentally assessed the impact of goldfish on the foraging behavior of both phenotypes of palmate newts (Lissotriton helveticus). More particularly, we assessed fish personality by analyzing the foraging activity and the aggressiveness toward newts, and newt personality by analyzing individual difference in boldness. In the presence of fish, fewer newts foraged than in their absence, and paedomorphs were more affected than metamorphs. We found strong personality differences in fish and fewer newts foraged in the presence of a more aggressive fish. Newts differed in boldness, but fish aggressiveness remains a key factor to explain newt behavior. Studying behavioral interactions between native and alien species helps to understand the mechanisms of coexistence and exclusion and why different phenotypes might be affected differently by the same threat. To a great extent, not only the presence of fish alters the foraging opportunities of newts but also the personality of the invader; integrating personality patterns of invaders is therefore a key to understanding the ecological consequences of alien species introduction.