Lateralization in seven lemur species when presented with a novel cognitive task.

Objectives: Asymmetrical behavior patterns are observed in many animal species, but the potential adaptive significance of lateralization and the evolutionary forces driving it remain unclear. Most laterality studies have focused on a single species, which makes interspecies comparisons difficult. The aim of this study was to examine differences in the strength and direction of lateralization in multiple lemur species when engaged in a standardized, novel cognitive task.

Materials And Methods: We assessed laterality in seven lemur species at the Duke Lemur Center when using a novel puzzle-box. We recorded which hand opened the apparatus door and which hand picked up the food reward. We also recorded whether the mouth was used for either action instead of the hands. We then calculated handedness indices (HI), z-scores, and mouth-use rates.

Results: Overall, 62% of individuals were more lateralized than chance. However, within-genera, there were relatively equal numbers of individuals with a left- or right-hand bias, which resulted in ambipreference at the genus level. The hand a lemur used on its first success in the task predicted its overall HI value, and the strength of lateralization increased as the number of successes increased. Varecia had significantly higher mouth-use rates than all other genera.

Discussion: We found evidence of an individual learning trajectory in which the hand used on a lemur's first success was canalized as the preferred (and lateralized) hand, in support of the "cognitive simplicity" hypothesis. Individual variability in hand preference was high, which is consistent with previous research. Between-genera differences in mouth use appear to reflect species-specific feeding postures and differences in manual dexterity.