Evol Ecol Res 19: 477-486 (2018) Full PDF if your library subscribes.
Cerebral lateralization and quantity discrimination abilities
in the threespine stickleback (Gasterosteus aculeatus)
Marion Mehlis-Rick, Timo Thünken, Markus Krings*, Simon Käfer# and Ingolf P. Rick
Institute for Evolutionary Biology and Ecology, University of Bonn, Bonn, Germany
Correspondence: I.P. Rick, Institute for Evolutionary Biology and Ecology, University of Bonn, An der Immenburg 1, 53121 Bonn, Germany. email: email@example.com
Background: The preferential use of one side of the body during behavioural activities (i.e. behavioural lateralization) is a consequence of functional cerebral asymmetries and can be found throughout the animal kingdom.
Hypothesis: Lateralization provides a selective advantage by conferring greater cognitive abilities on the organism.
Organism: Threespine stickleback (Gasterosteus aculeatus).
Methods: We gave individual fish the choice between two shoals differing in group size. We used the following numerical contrasts: 1 vs. 2 (small number/small ratio), 1 vs. 3 (small number/large ratio), 5 vs. 10 (large number/small ratio), and 5 vs. 15 (large number/large ratio). We manipulated eye availability by covering the fish’s right eye (left-monocular), covering the fish’s left eye (right-monocular), or leaving both eyes uncovered (binocular) during the choice trials. We measured the proportion of time the test fish spent in front of each of the two stimulus shoals.
Results: Sticklebacks generally preferred to shoal with the larger group. This preference was stronger at larger ratios. Quantity discrimination was not significantly restricted by monocular vision. In fact, left-monocular fish even tended to perform better than binocular conspecifics independent of contrast. Furthermore, when we separated the data by contrast, we found a significant effect of eye availability on shoaling preferences for the 5 vs. 10 contrast, i.e. fish with monocular vision performed similarly (right-monocular) or again better (left-monocular) at quantity discrimination compared with individuals that had both eyes uncovered. In comparison, eye occlusion had no significant effect on quantity discrimination in the other three contrasts (1 vs. 2, 1 vs. 3, and 5 vs. 15).
Conclusion: We found that cerebral lateralization is linked to certain numerical skills, which are of adaptive significance in different contexts, including shoaling, foraging, and predator avoidance.
Keywords: cerebral lateralization, cognitive abilities, Gasterosteus aculeatus, numerical contrasts, quantity discrimination, shoaling behaviour, threespine stickleback.
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