Assessing cognitive performance in nature: brain size and personality correlates of novel object recognition in nest-guarding male pumpkinseed sunfish

Keith McallisterMaria DolanCaleb J AxelrodBeren W RobinsonFrederic Laberge^*

• Integrative Biology, University of Guelph, Guelph, Ontario, Canada

Studying the factors that determine cognitive performance in animals is difficult to do in natural conditions, but necessary to ensure that the results of laboratory tests are relevant to wild populations. We took advantage of nest fidelity in parental male pumpkinseed sunfish (Lepomis gibbosus) to conduct a novel object recognition (NOR) assay in the field. We evaluated consistent individual differences in behaviour across the object familiarization and test phases of the NOR assay and sampled individuals following assay completion to obtain anatomical measurements, including brain size. We hypothesized that brain size would influence pumpkinseed cognitive ability and determine NOR performance after accounting for individual differences in behaviour. Parental males showed repeatable reactions to nest disturbance and to the presence of objects at the nest periphery between assay phases as well as correlated object investigation behaviours. We found evidence of novel object recognition memory at the level of the population, but it varied widely among individuals. Individual differences in object interactivity did not influence NOR performance, but relative brain mass (corrected for body length) did. Parental male pumpkinseed with relatively larger brains performed poorly in comparison with males with relatively smaller brains. We interpret this negative relationship between brain size and NOR performance in the context of severe energy limitations faced by parental males during reproduction. Namely, that males maintaining energetically costly larger brains are likely functioning at an upper limit without spare resources available to invest in costly learning processes. If true, this finding emphasizes that relationships between brain size and performance on cognitive tests may depend on energy availability and rate of expenditure.