Data from: Evolution of thermal tolerance in multifarious environments

Species extinction rates are many times greater than the direst
predictions made two decades ago by environmentalists, largely because of
human impact. Major concerns are associated with the predicted higher
recurrence and severity of extreme events, such as heat waves. Although
tolerance to these extreme events is instrumental to species survival,
little is known whether and how it evolves in natural populations, and to
what extent it is affected by other environmental stressors. Here, we
study physiological and molecular mechanisms of thermal tolerance over
evolutionary times in multifarious environments. Using the practice of
‘resurrection ecology’ on the keystone grazer Daphnia magna, we quantified
genetic and plastic differences in physiological and molecular traits
linked to thermal tolerance in historical and modern genotypes of the same
population. This population experienced an increase in average temperature
and occurrence of heat waves, in addition to dramatic changes in water
chemistry, over five decades. On genotypes resurrected across the five
decades, we measured plastic and genetic differences in CTmax, body size,
Hb content and differential expression of four heat shock proteins after
exposure to temperature as single stress and in combination with food
levels and insecticide loads. We observed evolution of the critical
thermal maximum and plastic response in body size, HSP expression and Hb
content over time in a warming only scenario. Molecular and physiological
responses to extreme temperature in multifarious environments were not
predictable from the response to warming alone. Underestimating the effect
of multiple stressors on thermal tolerance can lead to wrong estimates of
species evolvability and persistence.