Variable stressor exposure shapes fitness within and across generations

Environmental variation has long been considered a key driver of evolutionary change, predicted to shape different strategies, such as genetic specialization, plasticity, or bet-hedging to maintain fitness. However, little evidence is available with regards to how the periodicity of stressors may impact fitness across generations. To address this gap, I conducted a reciprocal split-brood experiment using the freshwater crustacean, Daphnia magna, and an ecologically relevant environmental stressor, ultraviolet radiation (UVR). I exposed one group to constant and another group to fluctuating UVR conditions. Despite receiving the same dose of UVR, the first experimental generation displayed significant treatment-by-genotype interactions with respect to survival and reproductive output, as well as a delayed reproductive maturity under fluctuating UVR conditions. In the following experimental generation individuals exposed to fluctuating UVR exhibited higher fitness than those in a constant ..., , , # Data from: Variable stressor exposure shapes fitness within and across generations

[https://doi.org/10.5061/dryad.m63xsj4cw](https://doi.org/10.5061/dryad.m63xsj4cw)

## Description of the data and file structure

To address how the variations of an environmental stressor may affect the life history of *Daphnia*, I quantified longevity, reproductive maturity, as defined by the first day at which eggs were visible in the brood pouch 52, and total reproductive output over each individual´s lifetime. Every individual was checked each day at the same time (±0.5 h). In order to take into account also the offspring’s ‘fitness’, I repeated this design for a second generation using a split brood design. Specifically, I took the first, third, fifth, and seventh broods forward to the next generation as to maximize the number of individuals in generation G4.

To assess UV in natural environments, data was collected via lowering a UV sensitive probe through the water column during the middle of ...,