Final Report Summary - E-RESPONSE (Evolutionary responses to a warming world: physiological genomics of seasonal timing) Climate change is strongly impacting seasonal timing but the shift in timing is unequal for species at different places in the food chain. This leads to natural selection on timing and a response to this selection is needed so that species can adapt to their warming world. This makes a better understanding of the potential for micro-evolution of timing in natural populations essential. But seasonal timing is the outcome of a complicated cascade of physiological mechanisms that start with the interaction between genes and the environment, leading to temporal patterns in RNA expression. To understand micro-evolution in timing, we thus need to unravel the genetics of the physiological mechanism underlying timing. For this highly integrated eco-evo-devo project we study the great tit (Parus major), an ecological and evolutionary model species for that we developed state-of-the-art genomic tools. A powerful tool to study the causes and consequences of genetic variation in timing of reproduction is to develop selection lines for egg laying date. We created such selection lines of early and late reproducing birds using genomic, rather than phenotypic, selection. This technique is used in animal breeding but had never been used for a wild species. After three generations we measured the birds laying dates in the breeding aviaries as well as in climate controlled aviaries and found that indeed the selection worked and that the birds from the late line laid later in aviaries than the early line. As a final test for the response to selection on laying date, eggs that formed the fourth generation of selection were taken to the wild and were placed in nests of foster parents. The chicks fledged and some returned to breed in the following years, when we could document their laying dates. Indeed, also in the wild, the early selection line birds laid earlier than the late selection line birds and it is thus clear that the genomic selection worked to create two lines of great tits which differed in their laying dates. To unravel how selection has altered the birds’ physiology we measured key components of the physiological mechanism at the central, peripheral and egg production levels, focussing on RNA expression patterns in birds, kept in climate controlled aviaries, that were repeatedly samples throughout the breeding season. The mRNA expression levels were measured using qPCR for a set of candidate genes associated with timing of reproduction and using RNAseq, analysing all genes, for samples pooled for three females. We found the differences between time points, and early and late laying females, exclusively in ovary and liver, showing that fine-tuning of seasonal timing of breeding, and thereby the opportunity for adaptation in the neuroendocrine system, is regulated mostly downstream in the neuro-endocrine system.As a unique next step, selection line birds have been introduced into a wild population to assess the fitness of these extreme phenotypes. Eggs from the fourth generation of selection were taken to wild foster parents and fledged in the wild. About 5% of the fledged offspring come back to breed and from these we can obtain laying dates and get a measure of their breeding success. Preliminary analysis show that indeed early line birds have a higher fitness than late line birds but only when additional data in 2020 and 2021 are collected (of birds already released in the wild) a more definite analysis can be done. There is however no reason to assume that the fitness differences as observed between early and late laying birds in our wild population are not causal and hence we use these data from our long-term population study to show that the expected and observed rate of micro-evolution in laying date due to climate change is very slow. It is thus possible to select for earlier timing of reproduction using genomic selection and that also in the wild such a response to selection is possible. This will have to work via genetic changes downstream in the physiological cascade underlying laying-date (the liver and gonads). However, these genetic changes will be slow, too slow to keep up with the rapid climate change that we are observing. It is therefore crucial to reduce the rate of climate change, as also agreed in the Paris treaty, as otherwise the rate of adaptation will fall short of the rate of change, which will have consequences for biodiversity.
