Contrasting effects of heat pulses on different trophic levels, an experiment with a herbivore-parasitoid model system

Abstract

Under predicted global climate change, species will be gradually exposed to warmer temperatures, and to a more variable climate including more intense and more frequent heatwaves. Increased climatic variability is expected to have different effects on species and ecosystems than gradual warming. A key challenge to predict the impact of climate change is to understand how temperature changes will affect species interactions. Herbivorous insects and their natural enemies belong to some of the largest groups of terrestrial animals, and thus they have a great impact on the functioning of ecosystems and on the services these ecosystems provide. Here we studied the life history traits of the plant-feeding insect Plutella xylostella and its specialist endoparasitoid Diadegma semiclausum, when exposed to a daily heat pulse of 5 or 10°C temperature increase during their entire immature phase. Growth and developmental responses differed with the amplitude of the heat pulse and they were different between host and parasitoid, indicating different thermal sensitivity of the two trophic levels. With a +5°C heat pulse, the adult parasitoids were larger which may result in a higher fitness, whereas a +10°C heat pulse retarded parasitoid development. These results show that the parasitoid is more sensitive than its host to brief intervals of temperature change, and this results in either positive or negative effects on life history traits, depending on the amplitude of the heat pulse. These findings suggest that more extreme fluctuations may disrupt host-parasitoid synchrony, whereas moderate fluctuations may improve parasitoid fitness.

Thermal plasticity potentially mediates the interaction between host Chilo partellus Swinhoe (Lepidoptera: Crambidae) and endoparasitoid Cotesia flavipes Cameron (Hymenoptera: Braconidae) in rapidly changing environments

“…Hence, the parasitoid may suffer more fitness costs and mortality as a consequence of repeated exposure to stressful conditions in nature, relative to its host C. partellus. 51,6 Acclimation to high temperature generally increased CT max in C. partellus and C. flavipes, consistent with the findings of previous studies on Ceratitis species, 32,50 Drosophilids 22 and Nezara species. 30 Mechanisms for improving CT max may comprise up-regulation of HSPs, consequently minimizing aggregation of denatured proteins following heat stress.…”

“…) shows that the parasitoid is more likely to survive under stressful high‐temperature conditions (≥35 °C) than its larval host (≥41 °C). Hence, the parasitoid may suffer more fitness costs and mortality as a consequence of repeated exposure to stressful conditions in nature, relative to its host C. partellus …”

“…As a consequence of global change, resistance to temperature stress in insects may be altered, with some organisms emerging ‘winners’ while others suffer harmful effects . Such alterations are found at different trophic levels, and are more common for herbivore parasitoid systems that show differential thermal sensitivity at different trophic levels . Insects employ a diverse range of morphological, physiological, and behavioral adaptations, or a combination of these mechanisms, to counter adverse climate conditions .…”

“…4 Such alterations are found at different trophic levels, and are more common for herbivore parasitoid systems that show differential thermal sensitivity at different trophic levels. 5,6 Insects employ a diverse range of morphological, physiological, and behavioral adaptations, or a combination of these mechanisms, to counter adverse climate conditions. 7,8 Physiologically, insects are known to survive extreme temperature variation through phenotypic plasticity, the ability of the same genotype to produce variable phenotypes in heterogeneous environments.…”

Mechanisms structuring host–parasitoid networks in a global warming context: a review

“…Global warming could modify host and parasitoid population dynamics (Jeffs & Lewis, 2013) by altering life-history traits such as developmental time, life span and winter diapause, for both hosts and parasitoids (Hance, 2007;Schreven et al, 2017;Tougeron et al, 2018). As host-parasitoid trophic interactions are typically specialised, and hosts and parasitoids often respond differently, this could disrupt phenological synchrony between hosts and parasitoids (Visser & Both, 2005;Klapwijk et al, 2010;Dyer et al, 2013).…”