Trait variability of the signal crayfish (Pacifastacus leniusculus) in a recently invaded region reflects potential benefits and trade-offs during dispersal

Rapid range expansion is one of the major attributes of invasion success. During range expansion, dispersing individuals face a novel environment where trade-offs between benefits of reduced conspecific density and pressure from niche competitors may differentially affect life-history traits essential for population growth. In this study, we examined differences in sex ratio, body condition, physiological condition and capacity for energetic investment into reproduction along an actively expanding range of one of the most successful crayfish invaders in Europe, the signal crayfish (Pacifastacus leniusculus). In the examined invasive range, signal crayfish faces competition by a native crayfish, Astacus leptodactylus. By comparing measured parameters between invasion fronts and invasion core sites, we analyzed whether the potential benefits of dispersal to areas with low conspecific density are outweighed by the competitive pressure from a native crayfish. Caught signal crayfish of both sexes from invasion fronts were in a better body condition compared to those from the invasion core, while females from invasion fronts also exhibited better energetic status of hepatopancreas and gonads. At the same time, A. leptodactylus from the contact zones at invasion fronts were in poorer body condition compared to those outside the invaded range. Thus, interspecific competition at invasion fronts affected the native A. leptodactylus more strongly than the signal crayfish, which still benefited from the reduced conspecific density in the presence of a competitor. This study highlights the importance of examining trait variability as invader advances its range, since a shift between the rate of population growth and counteracting pressure from other niche competitors could represent one of the crucial determinants of a lag between establishment and expansion of invasive species.