Transgenerational response to early spring warming in Daphnia

Temperature and photoperiod regulate key fitness traits in plants and animals. However, with temperature increase due to global warming, temperature cue thresholds are experienced at shorter photoperiods, disrupting the optimal seasonal timing of physiological, developmental and reproductive events in many species. Understanding the mechanisms of adaptation to the asynchrony between temperature and photoperiod is key to inform our understanding of how species will respond to rapid environmental change. Here, we studied the transgenerational mechanisms of responses of the cyclical parthenogen Daphnia magna to different photoperiod lengths co-occurring with warm temperature, thereby assessing the impact of earlier spring warming on fitness. Daphnia uses temperature and photoperiod cues to time dormancy and to switch between sexual and asexual reproduction. Moreover, its life cycle offers the opportunity to measure the relative contribution of plastic and genetic responses to environmental change across generations and over evolutionary time. We use transgenerational common garden experiments on three populations ‘resurrected’ from a biological archive experiencing temperature increase over five decades. Our results suggest that D. magna has the potential to evolve in response to early spring warming via a complex interaction between plastic and genetic mechanisms. The results also suggest a positive maternal effect in presence of matching environments between parental and offspring generation.