The heritability of spatial memory and caching behaviour in a food-storing bird.

Research examining how cognitive traits evolve in the wild has focussed on finding evidence of the 'Darwinian holy trinity'- consistent individual variation in cognitive performance that is linked to fitness and has a heritable component. In food-storing birds, there is growing evidence of selection for more accurate spatial memory performance. However, for selection to act on variation in spatial memory performance, it must also have a genetic component. In this study, we used Bayesian animal models to evaluate the heritability of memory performance in a spatial reference memory task in a population of wild toutouwai (North Island robin, Petroica longipes). We also estimated the heritability of variation in measures of the caching behaviour that spatial memory theoretically underpins. We found little evidence of heritability in either spatial memory performance or caching measures, as credible intervals were large with lower bounds close to zero. This result could suggest that individual variation in memory performance and caching behaviour may be primarily due to non-genetic factors. For example, variation in toutouwai spatial memory could be shaped largely by the cognitive demands of altering caching decisions in response to cache theft risk. In this scenario, the underlying mechanisms determining and linking spatial memory and caching behaviour would need to be reconsidered. Alternatively, the large credible intervals for our heritability estimates may be an artefact of small sample size. Therefore, to progress our understanding of how cognition evolves, it is crucial to establish long-term studies in the wild to collect cognitive performance data from as many individuals as possible over successive generations, with the goal of increasing the reliability of heritability estimates.