Life History Responses of Four Invasive Crayfish Species Under Prolonged Suboptimal Temperatures.

Biological invasions are strongly shaped by temperature, especially in poikilothermic organisms, where thermal regimes influence life-history traits, thereby determining both their competitive potential and geographic distribution. However, comparative evidence on how suboptimal thermal conditions modulate interactions among co-occurring invasive species remains scarce. We experimentally compared the growth, survival, and reproductive performance of the invasive parthenogenetic marbled crayfish Procambarus virginalis with three widespread North American crayfish invaders in Europe: the spiny-cheek crayfish Faxonius limosus, the signal crayfish Pacifastacus leniusculus, and the red swamp crayfish Procambarus clarkii. Experiments were conducted under prolonged suboptimal temperature conditions (∼16°C over 45 weeks), followed by a short-term temperature increase (∼20°C). Across three independent laboratory trials, we assessed species performance in single-species and mixed-species stocks. Despite reduced absolute growth rates at low temperature, marbled crayfish rapidly compensated for their initially smaller size and outperformed spiny-cheek crayfish in growth and survival. In contrast, marbled crayfish were consistently suppressed when co-occurring with the larger and more aggressive red swamp crayfish, whereas interactions with signal crayfish resulted in temporary growth advantages but ultimately size convergence. Survival patterns reflected a combination of size asymmetries, behavioral dominance, and intraspecific aggression, with marbled crayfish exhibiting notably high survival in single-species stocks across all trials. Reproductive development was strongly temperature-constrained. While marbled crayfish readily formed glair glands and ovulated eggs at 16°C, successful hatching occurred only after the temperature was raised. Our results demonstrate that suboptimal thermal conditions do not eliminate competitive asymmetries among invasive crayfish but instead reshape invasion outcomes in species-specific ways. These findings highlight the marbled crayfish's capacity to persist and interact competitively even in colder environments, with important implications for invasion dynamics under ongoing climate change.