Geographic differences in the phenology of gonadal development and moult, but not of egg laying, are genetically based in a small songbird

To forecast how fast populations can adapt to climate change, it is essential to determine the evolutionary potential of different life-cycle stages under selection. In birds, timing of gonadal development and moult are primarily regulated by photoperiod, while laying date is highly phenotypically plastic to temperature. We tested whether geographic variation in phenology of these life-cycle events between populations of great tits (Parus major) has a genetic basis, indicating that contemporary genetic adaptation is possible. We carried out a common garden experiment in which we bred first- and second-generation pairs in captivity originating from eggs from Gotland (Sweden) and Hoge Veluwe (Netherlands), two populations that showed different temperature sensitivity of laying date in a recent meta-analysis. We recorded the phenology of egg-laying, moult and gonadal size in early spring. We found no significant differences in laying date between the populations, but they did differ in mou..., Setting up common garden experiment
Birds: In the spring of 2021, freshly laid, unincubated eggs were transported from eight populations to the NIOO: La Rouvière (France), Boshoek (Belgium), Wytham Woods (England), Gotland (Sweden) and four Dutch populations (Hoge Veluwe, Vlieland, Oosterhout and Liesbos). The eggs were then taken to a Dutch population (Bennekomse Bos, lat: 52,003; long: 5,708) where they were placed in foster nests for incubating and early parental care.  At 10 days post-hatching, these chicks were transported to the Netherlands Institute of Ecology and hand raised, following procedures as outlined in [1]. They were blood sampled and based on their genotypes (using five microsatellite regions Pma-TGAn33, PmaC25, PmaTAGAn71, PmaGAn27 and PmaD10 [2]) and that of the potential parents, they were assigned to a family following a standard protocol [3].
For a number of these populations there were severe problems leading to very low numbers of chicks (see Appendix 1 for more..., , # Geographic differences in the phenology of gonadal development and moult, but not of egg laying, are genetically based in a small songbird

[https://doi.org/10.5061/dryad.zkh1893k8](https://doi.org/10.5061/dryad.zkh1893k8)

## Description of the data and file structure

To study to what extent geographic variation in laying date in great tits has a genetic basis, we carried out a two-generation common garden experiment in which we bred great tits that originated from eggs retrieved from two populations that in the Bailey et al. (2002, Nature Communications) analysis showed different temperature sensitivity. Such a common garden approach can show that there are genetic differences underlying this difference in sensitivity, as the confounding effects of different environments that shape the phenotype, as it occurs in the wild, are lifted. Such local adaptation would demonstrate that evolution has occurred over time, providing insights into the potential for genetic adaptation in current...