Behavioral trait (co)variances and plasticity in response to turbidity in wild zebrafish (Danio rerio)

The unpredictability of the environment can shape not only the mean behavioral expression but also the structure of behavioral variance within wild populations. Yet, empirical tests integrating individual variation, trait covariances, and correlated plasticities across ecologically relevant gradients remain rare, particularly those aimed at phenotype integration. Using wild zebrafish, we examined how long-term exposure to turbidity and immediate changes in water clarity influence behavioral means, individual (co)variances, and plasticity integration across three coping behaviors - activity, aggression, and boldness. Adult fish were conditioned in clear and turbid water for a month, followed by repeated behavioral tests in clear as well as in turbid water. Individuals that were maintained in clear or turbid water for a month showed substantial variation in their behavioral adjustments when exposed to perturbations in the water-clarity. Mean behaviors changed primarily in response to immediate change in water turbidity and trial repetition, not long-term conditioning. However, conditioning strongly altered individual variance structure; turbid-conditioned individuals showed reduced consistency across testing waters, indicating greater behavioral flexibility under sensory uncertainty. The only evidence to behavioral syndromes was between activity and boldness [r=-0.379] among clear-conditioned treatment, whereas within-individual correlations between aggression and boldness were prominent in turbid-conditioned fish. Despite substantial variation in behavioral plasticity, we detected no among-individual correlations in plasticity across traits. Together, these results demonstrate that turbidity modulates multi-scale behavioral variation, influencing how traits covary and integrate within individuals, and highlight how environmental unpredictability shapes flexibility in coping strategies.