Evolutionary time traveling in a changing world reveals ‘ecological surprises’

Twenty-five years ago, the Convention on Biological Diversity predicted over 30% of species extinction by 2100 because of human activities. Current evidence on species extinction exceeds this startling prediction. Major concerns are associated with the predicted higher recurrence and severity of extreme events as well as with the unpredictability of multifarious environments on biodiversity.
Using the practise of ‘resurrection ecology’ on the keystone grazer Daphnia magna, we study mechanisms of response to multiple anthropogenic stressors through evolutionary time. Using common garden experiments on resurrected populations, we test the impact of temperature as single stressor and in combination with food levels and insecticide loads on life history traits. Further, we measure trade-offs between constitutive and induced thermal tolerance in presence of warming alone and in combination with biotic and abiotic stress. This is done by quantifying genetic and plastic differences in critical thermal maximum (CTmax), body size, haemoglobin (Hb) content and heat shock proteins (HSP) expression between historical and modern genotypes of the same population that experienced increase in average temperature and occurrence of heat waves, in addition to dramatic changes in water chemistry over five decades.
We show that populations’ response to warming combined with biotic or abiotic stress on life history traits is not predictable from the effect of warming alone. We also reveal that in presence of warming alone, D. magna shows a positive correlation between constitutive and induced thermal tolerance mediated by evolutionary differences in the critical thermal maximum (CTmax). However, when warming co-occurs with other stressors (e.g. food stress) this positive correlation is disrupted, likely due to trade-offs imposed by multiple stressors. These results show that underestimating the effect of multiple stressors on thermal tolerance and using temperature as proxy for species response to global change can lead to wrong estimates of species evolvability and persistence