Habitat structural complexity predicts cognitive performance and behavior in western mosquitofish

Urban stream syndrome alters stream habitat complexity. We define habitat complexity as the degree of variation in physical habitat structure, with increasing variation equating to higher complexity. Habitat complexity affects species composition and shapes animal ecology, physiology, behavior, and cognition. We used a delayed detour test to measure whether cognitive processes (motor self-regulation) and behavior (risk-taking) of female Western mosquitofish, Gambusia affinis, varied with habitat structural complexity (low, moderate, and high) that was quantified visually for nine populations. We predicted that motor self-regulation and risk-taking behavior would increase with increasing habitat complexity, yet we found support for the opposite. Lower complexity habitats offer less refuge potentially leading to higher predation pressure and selecting for greater risk-taking by fish with higher motor self-regulation. Our findings provide insight into how habitat complexity can shape cognitive processes and behavior and offers a broader understanding of why some species may tolerate conditions of urbanized environments.