Epigenetic mechanisms can alter gene expression without a change in the nucleotide sequence and are increasingly recognized as important mechanisms that can generate phenotypic diversity. Most of our current knowledge regarding the origin and role of epigenetic variation comes from research on plants or mammals, often in controlled rearing conditions. Epigenetic research on birds in their natural habitats is still in its infancy, but is needed to answer questions regarding the origin of epigenetic marks and their role in phenotypic variation and evolution. Here we review the potential for studying epigenetic variation in natural bird systems. We aim to provide insights into (1) the origin of epigenetic variation, (2) the relationship between epigenetic variation and trait variation, and (3) the possible role of epigenetic variation in adaptation to changing environments. As there is currently little research on epigenetics in wild birds, we examine how findings on other taxa such as plants and mammals relate to birds. We also examine some of the pros and cons of the most commonly used methods to study patterns of DNA methylation in birds, and suggest some topics we believe need to be addressed to develop the field of wild avian epigenetics further. Zusammenfassung Anwendung von Epigenetik an freilebenden VögelnEpigenetische Mechanismen sind in der Lage die Aktivität eines Gens zu beeinflussen ohne die DNA-Sequenz zu veränderen und werden zunehmend als wichtige Mechanismen erkannt um phänotypische Diversität generieren zu können. Der größte Teil unseres derzeitigen Wissens über den Ursprung und die Rolle epigenetischer Variationen stammt aus der Erforschung von Pflanzen oder Säugetieren, oft unter kontrollierten Aufzuchtbedingungen. Die epigenetische Forschung an Vögeln in ihren natürlichen Lebensräumen steckt noch in den Kinderschuhen, ist jedoch erforderlich, um Fragen zur Herkunft der epigenetischen Merkmale und ihrer Rolle bei der Variation und Evolution des Phänotyps zu beantworten. Hier untersuchen wir das Potenzial zur Untersuchung der epigenetischen Variation in natürlichen Vogelsystemen. Wir möchten Einblicke geben in Communicated by M. Wink.

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.

No abstract

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.

No abstract