For over 50 years, the great tit (Parus major) has been a model species for research in evolutionary, ecological and behavioural research; in particular, learning and cognition have been intensively studied. Here, to provide further insight into the molecular mechanisms behind these important traits, we de novo assemble a great tit reference genome and whole-genome re-sequence another 29 individuals from across Europe. We show an overrepresentation of genes related to neuronal functions, learning and cognition in regions under positive selection, as well as increased CpG methylation in these regions. In addition, great tit neuronal non-CpG methylation patterns are very similar to those observed in mammals, suggesting a universal role in neuronal epigenetic regulation which can affect learning-, memory- and experience-induced plasticity. The high-quality great tit genome assembly will play an instrumental role in furthering the integration of ecological, evolutionary, behavioural and genomic approaches in this model species.

The design of artificial nestboxes for the study of secondary hole-nesting birds: a review of methodological inconsistencies and potential biases. Acta Ornithol. 45: 1-26.

Sperm cells are highly vulnerable to free radicals, and sperm quality and male fertility are critically affected by oxidative stress. Recently, sexual ornaments, particularly carotenoid-based colourful traits, have been proposed to depend on a male's capacity to resist oxidative stress, and thus to signal sperm quality. We conducted an experimental test of this hypothesis on great tits Parus major, in which adults are sexually dichromatic in carotenoid-based breast plumage. We report the first evidence that ornaments and sperm quality may be linked through oxidative stress. When experimentally subjected to oxidative stress resulting from increased workload, less colourful males suffered a greater reduction in sperm motility and swimming ability, and increased levels of sperm lipid peroxidation compared to more colourful males. Moreover, the level of sperm lipid peroxidation was negatively correlated with sperm quality. Finally, carotenoid supplementation increased sperm quality of less colourful males, suggesting that pale males are deficient in carotenoid antioxidants.

Maternal yolk androgens can promote growth and competitive abilities of nestling birds but are also suggested to increase susceptibility to parasites or suppress immune function. We tested the hypothesis that females exposed to ectoparasites during egg formation will adjust the content of androgens in the yolk. We predicted that when anticipating high levels of parasitism, females deposit (i) less androgens into all eggs of their clutch and (ii) smaller amounts of androgens in eggs late in the laying sequence to facilitate brood reduction.In a field experiment we exposed female great tits (Parus major) to hen fleas (Ceratophyllus gallinae), or kept them free of ectoparasites prior to egg laying. We collected the eggs and measured yolk concentrations of androstenedione (A4), testosterone (T) and 5α-dihydrotestosterone (DHT) by radioimmunoassay. Among clutches, eggs of ectoparasite-exposed females contained significantly less A4 and tended to contain less T, whereas DHT content was unaffected. Within clutches, content of A4 and T increased significantly with laying order whereas DHT content significantly decreased. These patterns were unaffected by ectoparasites.In summary, our results provide no evidence for hormone-based facilitation of brood reduction under ectoparasite exposure but support the hypothesis that females exposed to ectoparasites reduce levels of T and its precursor A4 in yolk and might thereby reduce the negative effects of parasites on offspring.

Summary1. Predation risk is known to influence behaviour and development, especially in breeding animals. Mothers may be selected to transfer information about the intensity of such risk to their offspring through maternal effects and thus influence their development. 2. Here, we test for this maternal effect via manipulation of perceived predation risk by exposing great tit females before and during ovulation to stuffed models and sounds of either a predator bird (sparrowhawk -Accipiter nisus) or of a non-predatory control (song thrush -Turdus philomelos) in their environment. Offspring of exposed mothers were then raised by foster parents subjected to no treatment in order to separate maternal effects from effects during post-hatching parental care. 3. Nestlings of mothers under increased predator density were smaller than those of control mothers yet showed higher growth rates of the wings. Additionally, first-year recruits from the predator treatment had longer wings at maturity. 4. This maternal effect may be a passive consequence of higher circulating stress hormone levels in mothers. The accelerated wing growth during the nestling stage may be a result of compensatory growth. 5. Alternatively, the accelerated wing growth, coupled with the longer wings at maturity, suggest that the maternal response to the environmental risk may be adaptive since lower weight and bigger wings are a selective advantage for predator evasion. In this case the maternal effect probably influences the distribution of resources to different growth functions in offspring. 6. We show for the first time through an environmental rather than a direct hormonal manipulation, that predation risk may elicit adaptive maternal effects in birds.