Cognitive individual differences are key in the network of trait covariance

Individual differences in cognition are widespread across animal taxa, and despite progress in identifying possible mechanisms shaping evolution and maintenance of this variation, significant gaps in our understanding persist. A crucial but often overlooked factor is the covariation between cognitive traits and traits from other domains, which can impose evolutionary constraints and drive indirect selection, shaping cognitive variance. To explore this factor, the present study investigated the covariation between cognitive, behavioral, physiological, and life-history traits in a wild-caught fish, the tench (Tinca tinca). We focused on 5 cognitive traits: motor lateralization, visual lateralization, spatial learning, cognitive flexibility, and memory. These cognitive traits were interrelated, with for instance, faster learners exhibiting lower cognitive flexibility. Additionally, cognitive traits correlated with several behavioral and physiological traits. Using a network analysis, we demonstrated the relevance of cognitive variance in the relationship among traits. Visual lateralization was central in the network, connecting subnetworks including behavioral and physiological traits. Memory was strongly linked to physiological traits. Last, spatial learning, cognitive flexibility, and visual lateralization were the traits with the highest impact in the whole network. Overall, our study not only highlights the complex associations between cognitive, behavioral and physiological, but also underscores the critical role of cognition in these relationships. This finding supports the idea that the evolution and maintenance of cognitive variance are both influenced by, and exert remarkably influence on, the variation in other traits.