Artificial selection for reversal learning reveals limited repeatability and no heritability of cognitive flexibility in great tits (Parus major).

Cognitive flexibility controls how animals respond to changing environmental conditions. Individuals within species vary considerably in cognitive flexibility but the micro-evolutionary potential in animal populations remains enigmatic. One prerequisite for cognitive flexibility to be able to evolve is consistent and heritable among-individual variation. Here we determine the repeatability and heritability of cognitive flexibility among great tits (Parus major) by performing an artificial selection experiment on reversal learning performance using a spatial learning paradigm over three generations. We found low, yet significant, repeatability (R = 0.15) of reversal learning performance. Our artificial selection experiment showed no evidence for narrow-sense heritability of associative or reversal learning, while we confirmed the heritability of exploratory behaviour. We observed a phenotypic, but no genetic, correlation between associative and reversal learning, showing the importance of prior information on reversal learning. We found no correlation between cognitive and personality traits. Our findings emphasize that cognitive flexibility is a multi-faceted trait that is affected by memory and prior experience, making it challenging to retrieve reliable values of temporal consistency and assess the contribution of additive genetic variation. Future studies need to identify what cognitive components underlie variation in reversal learning and study their between-individual and additive genetic components.

The epigenetics of animal personality.

Animal personality, consistent individual differences in behaviour, is an important concept for understanding how individuals vary in how they cope with environmental challenges. In order to understand the evolutionary significance of animal personality, it is crucial to understand the underlying regulatory mechanisms. Epigenetic marks such as DNA methylation are hypothesised to play a major role in explaining variation in phenotypic changes in response to environmental alterations. Several characteristics of DNA methylation also align well with the concept of animal personality. In this review paper, we summarise the current literature on the role that molecular epigenetic mechanisms may have in explaining personality variation. We elaborate on the potential for epigenetic mechanisms to explain behavioural variation, behavioural development and temporal consistency in behaviour. We then suggest future routes for this emerging field and point to potential pitfalls that may be encountered. We conclude that a more inclusive approach is needed for studying the epigenetics of animal personality and that epigenetic mechanisms cannot be studied without considering the genetic background.

Species- and size-related differences in dopamine-like immunoreactive clusters in the brain of Nasonia vitripennis and N. giraulti.

An extreme reduction in body size has been shown to negatively impact the memory retention level of the parasitic wasp Nasonia vitripennis. In addition, N. vitripennis and Nasonia giraulti, closely related parasitic wasps, differ markedly in the number of conditioning trials required to form long-term memory. These differences in memory dynamics may be associated with differences in the dopaminergic neurons in the Nasonia brains. Here, we used dopamine immunoreactivity to identify and count the number of cell bodies in dopaminergic clusters of normal- and small-sized N. vitripennis and normal-sized N. giraulti. We counted in total a maximum of approximately 160 dopaminergic neurons per brain. These neurons were present in 9 identifiable clusters (D1a, D1b, D2, D3, D4a, D4b, D5, D6 and D7). Our analysis revealed that N. giraulti had fewer cells in the D2 and D4a clusters but more in D4b, compared with normal-sized N. vitripennis. In addition, we found fewer cells in the D5 and D7 cluster of small-sized N. vitripennis compared to normal-sized N. vitripennis. A comparison of our findings with the literature on dopaminergic clusters in the fruit fly Drosophila melanogaster and the honey bee Apis mellifera indicates that clusters D2, D3 and D5 may play a role in memory formation in Nasonia wasps. The results from both the species comparison and the size comparison are therefore of high interest and importance for our understanding of the complex intricacies that underlie the memory dynamics of insects.