Interactions between developmental and adult acclimation have distinct consequences for heat tolerance and heat stress recovery

Evidence for transient deleterious thermal acclimation in field recapture rates of an invasive tropical species, Bactrocera dorsalis (Diptera: Tephritidae)

Knowing how environmental conditions affect performance traits in pest insects is important to improve pest management strategies. It can be informative for monitoring, but also for control programs where insects are mass-reared, and field-released. Here, we investigated how adult thermal acclimation in sterile Bactrocera dorsalis affects dispersal and recapture rates in the field using a mark-release-recapture method. We also considered how current abiotic factors may affect recapture rates and interact with thermal history. We found that acclimation at 20 or 30 °C for 4 d prior to release reduced the number of recaptures in comparison with the 25 °C control group, but with no differences between groups in the willingness to disperse upon release. However, the deleterious effects of acclimation were only detectable in the first week following release, whereafter only the recent abiotic conditions explained recapture rates. In addition, we found that recent field conditions contributed more than thermal history to explain patterns of recaptures. The two most important variables affecting the number of recaptures were the maximum temperature and the average relative humidity experienced in the 24 h preceding trapping. Our results add to the handful of studies that have considered the effect of thermal acclimation on insect field performance, but notably lend support to the deleterious acclimation hypothesis among the various hypotheses that have been proposed. Finally, this study shows that there are specific abiotic conditions (cold/hot and dry) in which recaptures will be reduced, which may therefore bias estimates of wild population size.

Warming during embryogenesis induces a lasting transcriptomic signature in fishes

Exposure to elevated temperatures during embryogenesis can influence the plasticity of tissues in later life. Despite these long-term changes in plasticity, few differentially expressed genes are ever identified, suggesting that the developmental programming of later life plasticity may occur through the modulation of other aspects of transcriptomic architecture, such as gene network organisation. Here, we use network modelling approaches to demonstrate that warm temperatures during embryonic development (developmental warming) have consistent effects in later life on the organisation of transcriptomic networks across four diverse species of fishes: Scyliorhinus canicula, Danio rerio, Dicentrarchus labrax, and Gasterosteus aculeatus. The transcriptomes of developmentally warmed fishes are characterised by an increased entropy of their pairwise gene interaction networks, implying a less structured, more 'random' set of gene interactions. We also show that, in zebrafish subject to developmental warming, the entropy of an individual gene within a network is associated with that gene's probability of expression change during temperature acclimation in later life. However, this association is absent in animals reared under 'control' conditions. Thus, the thermal environment experienced during embryogenesis can alter transcriptomic organisation in later life, and these changes may influence an individual's responsiveness to future temperature challenges.

The role of body mass in limiting post heat-coma recovery ability in terrestrial ectotherms

Under global warming, animal species show shrinking body size responses, cascading deep changes in community structure and ecosystem functions. Although the exact physiological mechanisms behind this phenomenon remain unsolved, smaller individuals may benefit from warming climate more than larger ones. Heat-coma, a physiological state with severe consequences on locomotion ability, is often considered as an "ecological death" scenario under which individuals are unable to escape and exposed to predation, further heat injury, and other hazards. Species are expected to increasingly encounter heat-coma temperature thresholds under warming climate, and body size may be an important trait for thermoregulation in particular for ectotherms. The relationship between heat-coma and shrinking body size remains, however, unclear. Yet, recovery after short-term heat-coma is possible, but little is known about its importance in thermal adaptation and how organismal size correlates with post heat-coma recovery. Here, using ants as a model system, we firstly examined the fate of heat-comatose individuals under field conditions to quantify the ecological benefits of post heat-coma recovery. Then, we quantified ants' recovery ability after heat-coma using a dynamic thermal assay in the laboratory and asked if thermal resilience varies between species with different body mass. Our results confirm that heat-coma represents an inherent ecological death where individuals failed to recover from coma suffer strong predation pressure. Additionally, following phylogenetic signals inclusion, organisms with small mass were more likely to recover, supporting the temperature-size rule in thermal adaptation and recent studies showing a decrease in body size composition of ectotherm community under warmer climatic conditions. Body size as a fundamental trait in ecology thus affects ectotherm survival under thermal stress, which may drive species body size adaptations and community composition under future warming scenarios.

Stress tolerance is influenced by artificial light at night during development and life-history strategy

Artificial light at night (ALAN) is increasingly prevalent worldwide, but life-history strategy may mitigate the costs of ALAN for animals. Yet, interactions among ALAN, life-history strategy and tolerance to climate-related stressors are unknown. We determined if developmental ALAN exposure (1) affects development, (2) affects adult phenotype, including heat and desiccation tolerance, and (3) affects and/or interacts with life-history strategy. We used the variable field cricket (Gryllus lineaticeps) because its geographic range is increasingly exposed to ALAN, heat, and drought conditions, and it exhibits different life-history strategies (flight-capability versus flight-incapability). ALAN affected adult phenotype, with positive effects on body mass (and size) and female reproductive investment, and a negative effect on heat tolerance. Life-history strategy also affected stress tolerance; flight-incapable females had greater heat tolerance and their desiccation tolerance was improved by ALAN exposure. Key features of environmental change (i.e. exposure to ALAN, heat and drought) may favor some life-history strategies over others.

Temperature-dependent plasticity mediates heart morphology and thermal performance of cardiac function in juvenile Atlantic salmon (Salmo salar)

In many fishes, upper thermal tolerance is thought to be limited in part by the heart's ability to meet increased oxygen demands during periods of high temperature. Temperature-dependent plasticity within the cardiovascular system may help fishes cope with the thermal stress imposed by increasing water temperatures. In this study, we examined plasticity in heart morphology and function in juvenile Atlantic salmon (Salmo salar) reared under control (+0°C) or elevated (+4°C) temperatures. Using noninvasive Doppler echocardiography, we measured the effect of acute warming on maximum heart rate, stroke distance, and derived cardiac output. A 4°C increase in average developmental temperature resulted in a>5°C increase in the Arrhenius breakpoint temperature for maximum heart rate and enabled the hearts of these fish to continue beating rhythmically to temperatures approximately 2°C higher than control fish. However, these differences in thermal performance were not associated with plasticity in maximum cardiovascular capacity, as peak measures of heart rate, stroke distance, and derived cardiac output did not differ between temperature treatments. Histological analysis of the heart revealed that while ventricular roundness and relative ventricle size did not differ between treatments, the proportion of compact myocardium in the ventricular wall was significantly greater in fish raised at elevated temperatures. Our findings contribute to the growing understanding of how the thermal environment can affect phenotypes later in life and identifies a morphological strategy that may help fishes cope with acute thermal stress.