Evaluation of life-history traits in Folsomia candida exposed to combined repeated mild heat shocks with phenanthrene

Climate change increases the frequency and intensity of extreme weather events. In nature, organisms are often exposed to climatic stressors and contaminants simultaneously, and the effects of contaminants may be modified by climate change and vice versa. Here, the effects of repeated mild heat shocks (0–5 times, 30 °C for 6 h), alone or combined with phenanthrene (PHE) (80 mg kg⁻¹ dry soil), on life-history traits of the springtail Folsomia candida were investigated. The survival, growth, maturation, and reproduction of single juvenile springtails were assessed over a period of 37 days. Increasing number of heat bouts or PHE exposure did not have significant negative effects on overall survival at the termination of the experiment, but the interaction between the two stressors led to complex interactions for the dynamics of survival during the test. Neither body growth nor time to first oviposition was influenced by heat or PHE, but a reduction of egg production with increasing number of heat bouts was observed, and there was an interaction between the two stressors. Further, a trade-off between the number of eggs produced and egg size was observed, indicating that females invested the same amount of energy in reproduction despite exposure to stressful temperature and PHE. These results indicate that egg production (in terms of the number of eggs) was a more sensitive indicator of the combined effects of mild heat shocks and PHE than growth, and there was a trade-off between survival and egg production.