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
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, behavioural 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.
