Most organisms organise their daily activities through circadian (i.e. day/night) clocks, which in turn are entrained to environmental information such as light. Circadian clocks allow organisms to anticipate daily events and are ubiquitous in nature. They “tick” at different rates in different individuals, thus showing variation in their properties, such as period length, which is highly heritable. But evolution of clocks is only possible if this variation is also associated with fitness differences. Currently, however, selection on clocks under natural conditions remain poorly understood, for this we need to study ‘wild clocks’.
We study the selection and evolution of circadian clocks in wild birds via measurements of rhythms in the wild and in the laboratory (using the chronobiology laboratory) and combine this information with pedigree, genomics and fitness data from our long-term populations. We also carry out experimental manipulations such as expose animals to distinct light schedules to test for causal effects.
The VENI project of Barbara Tomotani uses the process of urbanization as a natural experiment to test the prediction that by dramatically changing the environment, cities expose organisms to profoundly distinct selective pressures compared to their natural environment and select distinct clock properties. She measures individuals collected in cities and forests and carry out a large-scale common-garden study to separate genetic and environmental effects (using our climate controlled aviaries).
In her PhD project, Aurelia Strauss investigates the selection pressure on circadian systems in wild birds as well as the consistency of individual time-keeping between years and within pedigrees. Further, the performance of different chronotypes in response to environmental conditions will be examined. To study this, Aurelia records body temperature cycles and chronotypes of a wild Great Tit (Parus major) population on the island of Vlieland (NL) which has been subject to systematic long-term breeding studies. Thus, detailed data on pedigree and fitness in relation to phenotype can be used to quantify patterns of inheritance. Extreme early and late chronotypes will be experimentally tested for corresponding differences in circadian rhythms in captivity.