Resolving biological impacts of multiple heat waves: interaction of hot and recovery days

Abstract

Heat waves are increasing with global warming and have more dramatic biological effects on organisms in natural and agricultural ecosystems than mean temperature increase. However, predicting the impact of future heat waves on organisms and ecosystems is challenging because we still have a limited understanding of how the different components that characterize heat waves interact. Here we take an experimental approach to examine the individual and combine consequences of two important features that characterize heat waves: duration of successive hot days and recovery days between two hot spells. Specifically we exposed individuals of a global agricultural pest, the aphid Sitobion avenae to different heat wave scenarios by factorially manipulating the number of extreme hot days versus normal days and altered which period individuals experienced first in their life cycle. We found that effects of heat waves were driven by a delicate balance of damage during hot periods versus repair during normal periods. Increasing the duration of hot days in heat waves had a negative effect on various demographic rates and life‐time fitness of individuals, but magnitude of this effect was typically contingent on the temporal clustering of hot periods. Importantly, this interaction effect indicates that changes in the temporal distribution of extreme hot versus normal days can strongly alter the performance of organisms and dynamics of populations even when the total number of hot days during a given period remains unchanged. Together, these results emphasize the importance of accounting for the temporal distribution and quantitative patterns of extreme temperature events for predicting their consequences of natural and agricultural ecosystems.

Effect of short-term high-temperature exposure on the life history parameters of Ophraella communa

“…communa has a large thermal tolerance plasticity. These high survival rates may relate to recovery from heat injury during the cooler period between high temperatures or insufficient damage to affect survival 38 , which is common in insects 38 , 39 . It is believed that recovery times between high temperatures can allow injuries to be repaired, as aphids were shown to exhibit higher protein and osmolyte levels in a repeated exposure treatment compared to a prolonged exposure treatment group 39 .…”

Antioxidant Responses of Ragweed Leaf Beetle Ophraella communa (Coleoptera: Chrysomelidae) Exposed to Thermal Stress

“…The effects of heat stress on insects depend on the frequency, amplitude, and duration of the stress ( Ma et al, 2018 ), and the sex and developmental stage of the insect ( Enriquez and Colinet, 2017 ). It is reported that the frequency, intensity, and length of heat hot days will increase in the short- and in the long-term ( Ma et al, 2018 ).…”

“…The effects of heat stress on insects depend on the frequency, amplitude, and duration of the stress ( Ma et al, 2018 ), and the sex and developmental stage of the insect ( Enriquez and Colinet, 2017 ). It is reported that the frequency, intensity, and length of heat hot days will increase in the short- and in the long-term ( Ma et al, 2018 ). As an overlapping-generation species with a relatively short generation period ( Zhou et al, 2010 ), any developmental stage or the whole generation of O. communa might encounter phasic high-temperature stress.…”

“…Therefore, 40, 42, and 44°C for 3 h per day were selected, the treatment of 28°C was considered as control ( Zhou et al, 2010 ). The exposure periods continue for 3–5 (one developmental stage) or over 20 (one generation) days based on the developmental periods of different developmental stages of O. communa (4.0 days for the egg, 7.6 days for the larva, and 6.0 days for the pupa) earlier recorded at a constant high temperature (32°C) in laboratory ( Zhou et al, 2010 ) and the number of hot days (daily maximum temperature ≥ 40°C) at present and in the near future in China ( Zhang et al, 2015b ; Ma et al, 2018 ). The high-temperature exposures for each treatment were performed separately in environmental chambers (PRX-450D, Ningbo Haishu Safe Experimental Equipment Co., Ltd., Zhejiang, China) at 28 (control), 40, 42, or 44 ± 1°C, with a relative humidity of 70 ± 5%, a photoperiod of 14:10 (L:D) h ( Zhou et al, 2010 ), and a light intensity of 12,000 lx for 3 h daily.…”

“…Insects have an optimal temperature range to which their biological functions are best adapted; over this range, insects might suffer physiological costs and fitness decrease ( Jerbi-Elayed et al, 2015 ). Climate change has led to an increase in the frequency, intensity, and length of extreme high temperatures around the globe and this trend is expected to continue ( Ma et al, 2018 ). In many parts of China, summer daily maximum temperatures in the field often exceed 40°C for several hours, and the number of such hot days has also increased in the last few years ( Zhang et al, 2015b ).…”