Browsing by Author "Verberk, Wilco C. E. P."

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    Intraspecific variation of heat tolerance in a model ectotherm: The role of oxygen, cell size and body size
    (2023) Leiva, Félix P.; Santos, Mauro; Rezende Landaeta, Enrico; Verberk, Wilco C. E. P.
    Virtually all aspects of the biology of ectotherms are size-and temperature-dependent. Aerobic metabolism is often proposed to explain such relationships, with oxygen limitation setting limits to heat tolerance and constraining growth. However, experimental tests of the role of oxygen in heat tolerance have yielded mixed results, suggesting that oxygen limitation may be important only in certain contexts and on certain time scales but not others. Here, using thermal death time curves, which incorporate the intensity and duration of heat stress, we quantify the ability to survive heat stress in multiple inbred lines of Drosophila melanogaster, under normal and low oxygen conditions. The lines were selected to differ markedly in body size and cell size, as these traits have been hypothesised to shape thermal tolerance via their effects on oxygen supply and demand. Low oxygen condition markedly reduced survival time across inbred lines, especially when flies were exposed to prolonged, mild heat stress. Variations in heat tolerance among lines were partly related to cell size and body size differences, especially under chronic exposure to high temperatures, under hypoxia and in flies that exhibit larger cell size, supporting the idea that differences in cell size affect the oxygen supply and demand via differences in surface area to volume ratio. Because differences in heat tolerance were manifested at different timescales, our results underscore the need to close the gap between responses to acute timescales, typically employed in laboratory studies, and chronic timescales, which are ecologically more relevant.
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    Long-term forecast of thermal mortality with climate warming in riverine amphipods
    (2023) Verberk, Wilco C. E. P.; Hoefnagel, K. Natan; Peralta-Maraver, Ignacio; Floury, Mathieu; Rezende, Enrico L.
    Forecasting long-term consequences of global warming requires knowledge on thermal mortality and how heat stress interacts with other environmental stressors on different timescales. Here, we describe a flexible analytical framework to forecast mortality risks by combining laboratory measurements on tolerance and field temperature records. Our framework incorporates physiological acclimation effects, temporal scale differences and the ecological reality of fluctuations in temperature, and other factors such as oxygen. As a proof of concept, we investigated the heat tolerance of amphipods Dikerogammarus villosus and Echinogammarus trichiatus in the river Waal, the Netherlands. These organisms were acclimated to different temperatures and oxygen levels. By integrating experimental data with high-resolution field data, we derived the daily heat mortality probabilities for each species under different oxygen levels, considering current temperatures as well as 1 and 2? warming scenarios. By expressing heat stress as a mortality probability rather than a upper critical temperature, these can be used to calculate cumulative annual mortality, allowing the scaling up from individuals to populations. Our findings indicate a substantial increase in annual mortality over the coming decades, driven by projected increases in summer temperatures. Thermal acclimation and adequate oxygenation improved heat tolerance and their effects were magnified on longer timescales. Consequently, acclimation effects appear to be more effective than previously recognized and crucial for persistence under current temperatures. However, even in the best-case scenario, mortality of D. villosus is expected to approach 100% by 2100, while E. trichiatus appears to be less vulnerable with mortality increasing to 60%. Similarly, mortality risks vary spatially: In southern, warmer rivers, riverine animals will need to shift from the main channel toward the cooler head waters to avoid thermal mortality. Overall, this framework generates high-resolution forecasts on how rising temperatures, in combination with other environmental stressors such as hypoxia, impact ecological communities.