Learning is negatively associated with strength of left/right paw preference in wild grey squirrels (Sciurus carolinensis)

Abstract

Cerebral laterality, via hemispheric specialisation, has been evidenced across the animal kingdom and linked to cognitive performance in a number of species. Previously it has been suggested that cognitive processing is more efficient in brains with stronger hemispheric differences in processing, which may be the key fitness benefit driving the evolution of laterality. However, evidence supporting a positive association between cognitive performance and lateralization is mixed: data from studies of fish and birds show a positive relationship whereas more limited data from studies of mammals suggest a weak or even negative relationship, suggesting the intriguing possibility of a mammal/non-mammal divide in the nature of this relationship. Here, we report an empirical test examining the relationship between lateralization and cognitive performance in wild grey squirrels (Sciurus carolinensis) by measuring left/right paw preference as a behavioural assay of cerebral lateralization and learning speed as an assay of cognitive efficiency. We carried out a motor-based laterality test using a reaching paradigm and measured learning speed on a problem-solving task. In accordance with the suggestion of a mammal/non-mammal divide, we found a negative relationship between strength of paw preference and performance on the learning task. We discuss this finding in light of niche-specific adaptations, task-specific demands and cognitive flexibility.

Keywords: Cognition; Comparative cognition; Laterality; Lateralization; Learning; Paw preference.

Fig. 1

Schematic representation of the tube apparatus showing relevant dimensions

Fig. 2

Top: BF2E uses a paw to reach into the tube. Bottom: BABC performs an unsuccessful head attempt

Fig. 3

Laterality index scores for each squirrel. Dashed line shows mean value. Increased colour saturation indicates stronger lateralization, with blue indicating right-paw bias, red left-paw bias and grey ambidexterity

Fig. 4

Individual learning curves for each squirrel. Solid lines in the foreground show the fitted curve for each squirrel from a logistic regression modelling the proportion of paw attempts in each bout of ten trials, with the raw data shown as dots and connecting lines in the background. Dashed lines indicate predicted performance beyond the observed trials (based on extrapolation of the logistic curve). Colours for each squirrel correspond to those in Fig. 3

Fig. 5

Relationship between strength of laterality (AMB-LI) and predicted performance in bout 25 (as predicted from the learning curves in Fig. 4). Colours for each squirrel correspond to those in Fig. 3