Increasing temperature reduces decision accuracy by shifting speed-accuracy trade-offs in slower individuals

Cognitive responses are linked to consistent individual behavioural variation, but the potential impact of warming on this relationship remains unexplored. Within species, individuals show consistent behavioural differences that correlate with cognitive responses. Central to this are speed-accuracy trade-offs, where faster individuals typically make more errors than slower individuals. Because warming shifts ectotherms towards faster behavioural phenotypes, we tested whether elevated temperatures reduce accuracy. We measured decision-making in paradise fish (Macropodus opercularis) using a plus-maze task with differentially rewarded chambers, following a 15-day training period. Each fish was tested repeatedly across four non-extreme thermal conditions. We quantified accuracy (entering the rich reward chamber first) and latency (time to enter any chamber). Slower individuals achieved significantly higher accuracy than faster individuals, consistent with cognitive styles expectations. Warming, however, caused slower fish to become faster and less accurate, with a 62% reduction in their accuracy advantage between 23.4°C and 24.5°C, converging on the performance of constitutively faster individuals. Inhibitory control did not vary with temperature, suggesting that moderate warming affects accuracy through decision speed rather than direct effects on inhibitory control. These findings reveal a subtle mechanism by which climate warming may constrain cognitive diversity and adaptive flexibility in ectotherms.