Body size decline during thermal evolution is only detected at mild temperature

Body size is a key morphological trait that affects physiology and metabolism, as well as other relevant traits such as fertility and mating success. Some evidence points to a trend of shrinking body size with increasing temperature, but this is far from unequivocal. Here, we assess the evolution of body size under a warming environment in experimentally evolved Drosophila subobscura populations from two distinct geographical origins, tested in both ancestral and warming environments. We observed a decrease in body size in the warming populations, but only in the lower-latitude populations and only when tested in the ancestral (control) environment. The absence of a body size response in the warming environment may be owing to a balance between forces promoting thermodynamic stability-leading to a tendency for body size to decrease-and selection for increased reproductive output-leading to an increase in body size. Our findings indicate that body size variation is complex, with genotype-by-environment interactions occurring. This may explain the lack of consistency across studies. This highlights that predictions of body size evolution under climate warming are not straightforward and emphasizes the need for considering intra- and inter-specific variation in future studies.

Mean daily temperatures can predict the thermal limits of malaria transmission better than rate summation

Temperature shapes the distribution, seasonality, and magnitude of mosquito-borne disease outbreaks. Mechanistic models predicting transmission often use mosquito and pathogen thermal responses from constant temperature experiments. However, mosquitoes live in fluctuating environments. Rate summation (nonlinear averaging) is a common approach to infer performance in fluctuating environments, but its accuracy is rarely validated. We measured three mosquito traits that impact transmission (bite rate, survival, fecundity) in a malaria mosquito ( Anopheles stephensi ) across temperature gradients with three diurnal temperature ranges (0, 9 and 12°C). We compared thermal suitability models with temperature-trait relationships observed under constant temperatures, fluctuating temperatures, and those predicted by rate summation. We mapped results across An. stephenesi 's native Asian and invasive African ranges. We found: 1) daily temperature fluctuation significantly altered trait thermal responses; 2) rate summation partially captured decreases in performance near thermal optima, but also incorrectly predicted increases near thermal limits; and 3) while thermal suitability characterized across constant temperatures did not perfectly capture suitability in fluctuating environments, it was more accurate for estimating and mapping thermal limits than predictions from rate summation. Our study provides insight into methods for predicting mosquito-borne disease risk and emphasizes the need to improve understanding of organismal performance under fluctuating conditions.

Seasonal variation of behavioural thermoregulation in a fossorial salamander (Ambystoma maculatum)

Temperature seasonality plays a pivotal role in shaping the thermal biology of ectotherms. However, we still have a limited understanding of how ectotherms maintain thermal balance in the face of varying temperatures, especially in fossorial species. Due to thermal buffering underground, thermal ecology theory predicts relaxed selection pressure over thermoregulation in fossorial ectotherms. As a result, fossorial ectotherms typically show low thermoregulatory precision and low evidence of thermotactic behaviours in laboratory thermal gradients. Here, we evaluated how temperature selection (T sel) and associated behaviours differed between seasons in a fossorial amphibian, the spotted salamander (Ambystoma maculatum). By comparing thermoregulatory parameters between the active and overwintering seasons, we show that A. maculatum engages in active behavioural thermoregulation despite being fossorial. In both seasons, T sel was consistently offset higher than acclimatization temperatures. Thermoregulation differed between seasons, with salamanders having higher T sel and showing greater evidence of thermophilic behaviours in the active compared with the overwintering season. Additionally, our work lends support to experimental assumptions commonly made but seldom tested in thermal biology studies. Ultimately, our study demonstrates that the combination of careful behavioural and thermal biology measurements is a necessary step to better understand the mechanisms that underlie body temperature control in amphibians.

Physiologically-informed predictions of climate warming effects on native and non-native populations of blue catfish

Blue catfish Ictalurus furcatus has been widely introduced throughout the United States to enhance recreational fisheries. Its success in both its native and non-native range, especially in the context of climate change, will be influenced by its thermal performance. We conducted a laboratory experiment to investigate the responses of wild-captured, subadult blue catfish to temperatures ranging from 7 °C to 38 °C. Blue catfish had relatively low standard metabolic rates, indicating low energetic demands, and hence an ability to survive well even during low-food conditions. Metabolic scope and food consumption rate increased with temperature, with metabolic scope peaking at 29.1 °C, and consumption rate peaking at 32 °C. Body condition remained high up to 32 °C, but decreased drastically thereafter, suggesting limitations in maintaining metabolism through food consumption at temperatures >32 °C; blue catfish cannot survive in such habitats indefinitely. Yet, many fish were able to survive temperatures as high as 38 °C for 5 days, suggesting that acute and occasionally chronic heat waves will not limit this species. Using these results, we also predicted the performance of blue catfish under prevailing conditions and under climate warming at seven locations throughout their current range in the U.S. We found that some blue catfish populations in southern and southeastern areas will likely experience temperatures above the optimal temperature for extended periods due to climate change, thus limiting potential habitat availability for this species. But, many non-native populations, especially those in northern areas such as Idaho, North Dakota, and northern California, may benefit from the expected warmer temperatures during spring and fall.

Larval diet impacts black soldier fly (Diptera: Stratiomyidae) thermal tolerance and preference

Thermal tolerance and preference are key parameters impacting agricultural production systems. In this study, the impact of larval diet on black soldier fly thermal tolerance and preference across life-stages and sexes was examined. Larvae were fed either a low-protein high-carbohydrate synthetic diet (i.e., P7C35), a high-protein low-carbohydrate synthetic diet (i.e., P35C7), or the Gainesville diet (i.e., C) as a control and reference. Our results demonstrate that the impacts of larval diet on black soldier fly thermal tolerance and preference could be stage and sex specific. The mean heat knockdown temperatures (HKT) ranged between 46.6 and 47.9 °C. Synthetic diets resulted in greater HKT and the difference decreased form larvae (e.g., ∼1 °C) to adults (e.g., ∼0.2 °C). The mean chill-coma recovery time (CCRT) ranged between 8.3 and 21.6 min. Not much differences were detected between diets, but CCRT became longer from larvae to adults. The mean thermal preference ranged between 13.6 and 29.5 °C. Larvae fed synthetic diets preferred much lower temperatures than the control diet. A bimodal distribution was observed for adults regardless of sex. Differences on body mass, lipid, and protein contents were detected among diets; however, more research should be done before any conclusions can be linked to their thermal traits. These findings highlight the importance of considering the ingredients and nutritional makeup of larval diets when optimizing temperature management protocols for mass production of black soldier flies. Conversely, specific diets can be developed to promote survival under extreme rearing temperatures.

Physiological thermal responses of three Mexican snakes with distinct lifestyles

The impact of temperature on reptile physiology has been examined through two main parameters: locomotor performance and metabolic rates. Among reptiles, different species may respond to environmental temperatures in distinct ways, depending on their thermal sensitivity. Such variation can be linked to the ecological lifestyle of the species and needs to be taken into consideration when assessing the thermal influence on physiology. This is particularly relevant for snakes, which are a very functionally diverse group. In this study, our aim was to analyze the thermal sensitivity of locomotor performance and resting metabolic rate (RMR) in three snake species from central Mexico (Crotalus polystictus, Conopsis lineata, and Thamnophis melanogaster), highlighting how it is influenced by their distinctive behavioral and ecological traits. We tested both physiological parameters in five thermal treatments: 15 °C, 25 °C, 30 °C, 33 °C, and 36 °C. Using the performance data, we developed thermal performance curves (TPCs) for each species and analyzed the RMR data using generalized linear mixed models. The optimal temperature for locomotion of C. polystictus falls near its critical thermal maximum, suggesting that it can maintain performance at high temperatures but with a narrow thermal safety margin. T. melanogaster exhibited the fastest swimming speeds and the highest mass-adjusted RMR. This aligns with our expectations since it is an active forager, a high energy demand mode. The three species have a wide performance breadth, which suggests that they are thermal generalists that can maintain performance over a wide interval of temperatures. This can be beneficial to C. lineata in its cold habitat, since such a characteristic has been found to allow some species to maintain adequate performance levels in suboptimal temperatures. RMR increased along with temperature, but the proportional surge was not uniform since thermal sensitivity measured through Q10 increased at the low and high thermal treatments. High Q10 at low temperatures could be an adaptation to maintain favorable performance in suboptimal temperatures, whereas high Q10 at high temperatures could facilitate physiological responses to heat stress. Overall, our results show different physiological adaptations of the three species to the environments they inhabit. Their different activity patterns and foraging habits are closely linked to these adaptations. Further studies of other populations with different climatic conditions would provide valuable information to complement our current understanding of the effect of environmental properties on snake physiology.

Hydration state does not affect selected body temperature during gravidity or gravidity duration in pythons (Antaresia childreni)

The embryonic development of many ectothermic species are highly sensitive to temperature and typically have a higher thermal optima than do most other physiological processes. Thus, female ectotherms often maintain a higher and more carefully controlled body temperature when she is supporting developing embryos (early development in oviparous species, throughout development in viviparous species). Considering the positive correlation between body temperature and evaporative water loss, this response could potentially exacerbate female water imbalance in water-limited environments, suggesting that female water balance and egg development may be in conflict. Using Children's pythons (Antaresia childreni), we hypothesized that water deprivation reduces thermophily during gravidity. We split reproductive females into two thermal treatments: those provided with a continuously available thermal gradient of 25-45 °C and those kept at a constant 31 °C. We also had seven non-reproductive females that were provided a thermal gradient. Within each thermal treatment group, we alternatingly assigned females to either have or not have water throughout gravidity. We found that reproduction increased female body temperature, but this increase was not affected by water regime. Reproduction also increased plasma osmolality, and lack of water during gravidity exacerbated this effect. We also found that thermal treatment, but not water regime, significantly influenced gravidity duration, with females given a thermogradient having a shorter gravidity duration, likely as a result of having a higher average body temperature than did the females provided constant heat. Finally, we found that females provided water throughout gravidity had greater clutch masses than did females without water. Further research is needed to improve scientific understanding of the interactions among water balance, body temperature, and various physiological performances.

Mosquito population dynamics is shaped by the interaction among larval density, season, and land use

Understanding how variation in key abiotic and biotic factors interact at spatial scales relevant for mosquito fitness and population dynamics is crucial for predicting current and future mosquito distributions and abundances, and the transmission potential for human pathogens. However, studies investigating the effects of environmental variation on mosquito traits have investigated environmental factors in isolation or in laboratory experiments that examine constant environmental conditions that often do not occur in the field. To address these limitations, we conducted a semi-field experiment in Athens, Georgia using the invasive Asian tiger mosquito (Aedes albopictus). We selected nine sites that spanned natural variation in impervious surface and vegetation cover to explore effects of the microclimate (temperature and humidity) on mosquitoes. On these sites, we manipulated conspecific larval density at each site. We repeated the experiment in the summer and fall. We then evaluated the effects of land cover, larval density, and time of season, as well as interactive effects, on the mean proportion of females emerging, juvenile development time, size upon emergence, and predicted per capita population growth (i.e., fitness). We found significant effects of larval density, land cover, and season on all response variables. Of most note, we saw strong interactive effects of season and intra-specific density on each response variable, including a non-intuitive decrease in development time with increasing intra-specific competition in the fall. Our study demonstrates that ignoring the interaction between variation in biotic and abiotic variables could reduce the accuracy and precision of models used to predict mosquito population and pathogen transmission dynamics, especially those inferring dynamics at finer-spatial scales across which transmission and control occur.

Response to von Schmalensee et al

Von Schmalensee et al. present two concerns about our study. While the first stems from a general disagreement about our simulation methodology, the second is a useful observation of a modelling choice we made that affected simulation outcomes, but in ways that do not invalidate our original conclusions.

Methodological artefacts cause counter-intuitive evolutionary conclusions in a simulation study

In their simulation study, Garcia-Costoya et al. (2023) conclude that evolutionary constraints might aid populations facing climate change. However, we are concerned that this conclusion is largely a consequence of the simulated temperature variation being too small, and, most importantly, that uneven limitations to standing variation disadvantage unconstrained populations.

Latitudinal variation in thermal performance of the common coral Pocillopora spp

Understanding how tropical corals respond to temperatures is important to evaluating their capacity to persist in a warmer future. We studied the common Pacific coral Pocillopora over 44° of latitude, and used populations at three islands with different thermal regimes to compare their responses to temperature using thermal performance curves (TPCs) for respiration and gross photosynthesis. Corals were sampled in the local autumn from Moorea, Guam and Okinawa, where mean±s.d. annual seawater temperature is 28.0±0.9°C, 28.9±0.7°C and 25.1±3.4°C, respectively. TPCs for respiration were similar among latitudes, the thermal optimum (Topt) was above the local maximum temperature at all three islands, and maximum respiration was lowest at Okinawa. TPCs for gross photosynthesis were wider, implying greater thermal eurytopy, with a higher Topt in Moorea versus Guam and Okinawa. Topt was above the maximum temperature in Moorea, but was similar to daily temperatures over 13% of the year in Okinawa and 53% of the year in Guam. There was greater annual variation in daily temperatures in Okinawa than Guam or Moorea, which translated to large variation in the supply of metabolic energy and photosynthetically fixed carbon at higher latitudes. Despite these trends, the differences in TPCs for Pocillopora spp. were not profoundly different across latitudes, reducing the likelihood that populations of these corals could better match their phenotypes to future more extreme temperatures through migration. Any such response would place a premium on high metabolic plasticity and tolerance of large seasonal variations in energy budgets.

Thermal ecology shapes disease outcomes of entomopathogenic fungi infecting warm-adapted insects

The thermal environment is a critical determinant of outcomes in host-pathogen interactions, yet the complexities of this relationship remain underexplored in many ecological systems. We examined the Thermal Mismatch Hypothesis (TMH) by measuring phenotypic variation in individual thermal performance profiles using a model system of two species of entomopathogenic fungi (EPF) that differ in their ecological niche, Metarhizium brunneum and M. flavoviride, and a warm-adapted model host, the mealworm Tenebrio molitor. We conducted experiments across ecologically relevant temperatures to determine the thermal performance curves for growth and virulence, measured as % survival, identify critical thresholds for these measures, and elucidate interactive host-pathogen effects. Both EPF species and the host exhibited a shared growth optima at 28 °C, while the host's growth response was moderated in sublethal pathogen infections that depended on fungus identity and temperature. However, variances in virulence patterns were different between pathogens. The fungus M. brunneum exhibited a broader optimal temperature range (23-28 °C) for virulence than M. flavoviride, which displayed a multiphasic virulence-temperature relationship with distinct peaks at 18 and 28 °C. Contrary to predictions of the TMH, both EPF displayed peak virulence at the host's optimal temperature (28 °C). The thermal profile for M. brunneum aligned more closely with that of T. molitor than that for M. flavoviride. Moreover, the individual thermal profile of M. flavoviride closely paralleled its virulence thermal profile, whereas the virulence thermal profile of M. brunneum did not track with its individual thermal performance. This suggests an indirect, midrange (23 °C) effect, where M. brunneum virulence exceeded growth. These findings suggest that the evolutionary histories and ecological adaptations of these EPF species have produced distinct thermal niches during the host interaction. This study contributes to our understanding of thermal ecology in host-pathogen interactions, underpinning the ecological and evolutionary factors that shape infection outcomes in entomopathogenic fungi. The study has ecological implications for insect population dynamics in the face of a changing climate, as well as practically for the use of these organisms in biological control.

Food web trophic control modulates tropical Atlantic reef ecosystems response to marine heat wave intensity and duration

Marine heatwaves (MHWs) are episodes of anomalous warming in the ocean that can last from a few days to years. MHWs have different characteristics in terms of intensity, duration and frequency and generate thermal stress in marine ecosystems. In reef ecosystems, they are one of the main causes of the decreased presence and abundance of corals, invertebrates and fish. The deleterious capacity of thermal stress often depends on biotic factors, such as the trophic control of predators on prey. Despite the evidence of thermal stress and biotic factors affecting individual species, the combined effects of both stressors on entire reef ecosystems are much less studied. Here, using a food web modelling approach, we estimated the rate of change in species' biomass due to different MHW characteristics. Specifically, we modelled the mechanistic link between species' consumption rate and seawater temperature (thermal stressor), simulating species' biomass dynamics for different MHW characteristics under different trophic control assumptions (top-down, mixed trophic control and bottom-up). We find that total reef ecosystem biomass declined by 10% ± 5% under MHWs with severe intensity and a top-down control assumption. The bottom-up control assumption moderates the total ecosystem biomass reduction by 5% ± 5%. Irrespective of the MHW characteristics and the trophic control assumption, the most substantial biomass changes occur among top, mesopredators and corals (5% to 20% ± 10%). We show that reef ecosystems where predators exert top-down control on prey are prone to suffer species abundance declines under strong MHW events. We identify food web trophic control as a crucial driver that modulates the impacts of MHWs. Overall, our results provide a unified understanding of the interplay between abiotic stressors and biotic factors in reef ecosystems under extreme thermal events, offering insights into present baselines and future ecological states for reef ecosystems.

Daily temperature fluctuation interacts with the mean temperature to increase the toxicity of a pyrethroid insecticide in a moth

Climate change complicates ecotoxicology studies because species responses to pesticides depend on temperature. Classically illustrated by the effect of constant laboratory temperatures, a recent review revealed that the toxicity of pesticides is also often increased by daily temperature fluctuations. Here, we investigated the combined effects of daily temperature fluctuation and mean temperature on the toxicity of two insecticides in the moth Spodoptera littoralis. Our study tested the toxicity of chlorpyrifos and deltamethrin on larvae of six experimental groups that crossed three treatments of daily temperature fluctuations (0, 5 or 10 °C) and two treatments of mean temperatures (25 or 33 °C). We showed that daily temperature fluctuation increased larval mortality induced by chlorpyrifos and deltamethrin. However, the response differed between the organophosphorus insecticide chlorpyrifos and the pyrethroid insecticide deltamethrin. The increase in chlorpyrifos toxicity by daily temperature fluctuation did not differ between mean temperatures of 25 and 33 °C. Remarkably, the increase in deltamethrin toxicity by daily temperature fluctuation was dependent on the crossed effects of the amplitude of daily fluctuation and mean temperature. This increase in deltamethrin toxicity occurred with a daily fluctuation of only 5 °C for larvae reared at 25 °C and a daily fluctuation of 10 °C in larvae reared at 33 °C. To confidently quantify the responses of insecticide toxicity to temperature, future ecotoxicology studies will have to evaluate the generality of the interaction between the effects of daily temperature fluctuation and mean temperature.

The cliff edge model of the evolution of schizophrenia: Mathematical, epidemiological, and genetic evidence

How has schizophrenia, a condition that significantly reduces an individual's evolutionary fitness, remained common across generations and cultures? Numerous theories about the evolution of schizophrenia have been proposed, most of which are not consistent with modern epidemiological and genetic evidence. Here, we briefly review this evidence and explore the cliff edge model of schizophrenia. It suggests that schizophrenia is the extreme manifestation of a polygenic trait or a combination of traits that, within a normal range of variation, confer cognitive, linguistic, and/or social advantages. Only beyond a certain threshold, these traits precipitate the onset of schizophrenia and reduce fitness. We provide the first mathematical model of this qualitative concept and show that it requires only very weak positive selection of the underlying trait(s) to explain today's schizophrenia prevalence. This prediction, along with expectations about the effect size of schizophrenia risk alleles, are surprisingly well matched by empirical evidence. The cliff edge model predicts a dynamic change of selection of risk alleles, which explains the contradictory findings of evolutionary genetic studies.

How seasonality influences the thermal biology of lizards with different thermoregulatory strategies: a meta-analysis

Ectotherms that maintain thermal balance in the face of varying climates should be able to colonise a wide range of habitats. In lizards, thermoregulation usually appears as a variety of behaviours that buffer external influences over physiology. Basking species rely on solar radiation to raise body temperatures and usually show high thermoregulatory precision. By contrast, species that do not bask are often constrained by climatic conditions in their habitats, thus having lower thermoregulatory precision. While much focus has been given to the effects of mean habitat temperatures, relatively less is known about how seasonality affects the thermal biology of lizards on a macroecological scale. Considering the current climate crisis, assessing how lizards cope with temporal variations in environmental temperature is essential to understand better how these organisms will fare under climate change. Activity body temperatures (Tb ) represent the internal temperature of an animal measured in nature during its active period (i.e. realised thermal niche), and preferred body temperatures (Tpref ) are those selected by an animal in a laboratory thermal gradient that lacks thermoregulatory costs (i.e. fundamental thermal niche). Both traits form the bulk of thermal ecology research and are often studied in the context of seasonality. In this study, we used a meta-analysis to test how environmental temperature seasonality influences the seasonal variation in the Tb and Tpref of lizards that differ in thermoregulatory strategy (basking versus non-basking). Based on 333 effect sizes from 137 species, we found that Tb varied over a greater magnitude than Tpref across seasons. Variations in Tb were not influenced by environmental temperature seasonality; however, body size and thermoregulatory strategy mediated Tb responses. Specifically, larger species were subjected to greater seasonal variations in Tb , and basking species endured greater seasonal variations in Tb compared to non-basking species. On the other hand, the seasonal variation in Tpref increased with environmental temperature seasonality regardless of body size. Thermoregulatory strategy also influenced Tpref , suggesting that behaviour has an important role in mediating Tpref responses to seasonal variations in the thermal landscape. After controlling for phylogenetic effects, we showed that Tb and Tpref varied significantly across lizard families. Taken together, our results support the notion that the relationship between thermal biology responses and climatic parameters can be taxon and trait dependent. Our results also showcase the importance of considering ecological and behavioural aspects in macroecological studies. We further highlight current systematic, geographical, and knowledge gaps in thermal ecology research. Our work should benefit those who aim to understand more fully how seasonality shapes thermal biology in lizards, ultimately contributing to the goal of elucidating the evolution of temperature-sensitive traits in ectotherms.

How turtles keep their cool: Seasonal and diel basking patterns in a tropical turtle

Behavioural thermoregulation by ectotherms is an important mechanism for maintaining body temperatures to optimise physiological performance. Experimental studies suggest that nocturnal basking by Krefft's river turtles (Emydura macquarii krefftii) in the tropics may allow them to avoid high water temperatures, however, this hypothesis has yet to be tested in the field. In this study, we examined the influence of environmental temperature on seasonal and diel patterns of basking in E. m. krefftii in tropical north Queensland, Australia. Wildlife cameras were used to document turtle basking events for seven consecutive days and nights for each month over a year (April 2020-March 2021). Air and water temperatures were recorded simultaneously using temperature loggers. We used a negative binomial mixed effects model to compare mean basking durations (min) occurring among four environmental temperature categories based on population thermal preference (26 °C): 1) air temperature above and water temperature below preferred temperature; 2) air temperature below and water temperature above preferred temperature; 3) air and water temperatures both above preferred temperature; and 4) air and water temperatures both below preferred temperature. Basking behaviour was influenced significantly by the relationship between air and water temperature. During the day, turtles spent significantly less time basking when both air and water temperatures were above their preferred temperatures. Conversely, at night, turtles spent significantly more time basking when water temperatures were warm and air temperatures were cool relative to their preferred temperature. This study adds to the growing body of work indicating pronounced heat avoidance as a thermoregulatory strategy among tropical reptile populations.

Does heat tolerance actually predict animals' geographic thermal limits?

The "climate extremes hypothesis" is a major assumption of geographic studies of heat tolerance and climatic vulnerability. However, this assumption remains vastly untested across taxa, and multiple factors may contribute to uncoupling heat tolerance estimates and geographic limits. Our dataset includes 1000 entries of heat tolerance data and maximum temperatures for each species' known geographic limits (hereafter, Tmax). We gathered this information across major animal taxa, including marine fish, terrestrial arthropods, amphibians, non-avian reptiles, birds, and mammals. We first tested if heat tolerance constrains the Tmax of sites where species could be observed. Secondly, we tested if the strength of such restrictions depends on how high Tmax is relative to heat tolerance. Thirdly, we correlated the different estimates of Tmax among them and across species. Restrictions are strong for amphibians, arthropods, and birds but often weak or inconsistent for reptiles and mammals. Marine fish describe a non-linear relationship that contrasts with terrestrial groups. Traditional heat tolerance measures in thermal vulnerability studies, like panting temperatures and the upper set point of preferred temperatures, do not predict Tmax or are inversely correlated to it, respectively. Heat tolerance restricts the geographic warm edges more strongly for species that reach sites with higher Tmax for their heat tolerance. These emerging patterns underline the importance of reliable species' heat tolerance indexes to identify their thermal vulnerability at their warm range edges. Besides, the tight correlations of Tmax estimates across on-land microhabitats support a view of multiple types of thermal challenges simultaneously shaping ranges' warm edges for on-land species. The heterogeneous correlation of Tmax estimates in the ocean supports the view that fish thermoregulation is generally limited, too. We propose new hypotheses to understand thermal restrictions on animal distribution.

Plasticity of Gene Expression and Thermal Tolerance: Implications for Climate Change Vulnerability in a Tropical Forest Lizard

AbstractTropical ectotherms are thought to be especially vulnerable to climate change because they have evolved in temporally stable thermal environments and therefore have decreased tolerance for thermal variability. Thus, they are expected to have narrow thermal tolerance ranges, live close to their upper thermal tolerance limits, and have decreased thermal acclimation capacity. Although models often predict that tropical forest ectotherms are especially vulnerable to rapid environmental shifts, these models rarely include the potential for plasticity of relevant traits. We measured phenotypic plasticity of thermal tolerance and thermal preference as well as multitissue transcriptome plasticity in response to warmer temperatures in a species that previous work has suggested is highly vulnerable to climate warming, the Panamanian slender anole lizard (Anolis apletophallus). We found that many genes, including heat shock proteins, were differentially expressed across tissues in response to short-term warming. Under long-term warming, the voluntary thermal maxima of lizards also increased, although thermal preference exhibited only limited plasticity. Using these data, we modeled changes in the activity time of slender anoles through the end of the century under climate change and found that plasticity should delay declines in activity time by at least two decades. Our results suggest that slender anoles, and possibly other tropical ectotherms, can alter the expression of genes and phenotypes when responding to shifting environmental temperatures and that plasticity should be considered when predicting the future of organisms under a changing climate.

Variation in temperature of peak trait performance constrains adaptation of arthropod populations to climatic warming

The capacity of arthropod populations to adapt to long-term climatic warming is currently uncertain. Here we combine theory and extensive data to show that the rate of their thermal adaptation to climatic warming will be constrained in two fundamental ways. First, the rate of thermal adaptation of an arthropod population is predicted to be limited by changes in the temperatures at which the performance of four key life-history traits can peak, in a specific order of declining importance: juvenile development, adult fecundity, juvenile mortality and adult mortality. Second, directional thermal adaptation is constrained due to differences in the temperature of the peak performance of these four traits, with these differences expected to persist because of energetic allocation and life-history trade-offs. We compile a new global dataset of 61 diverse arthropod species which provides strong empirical evidence to support these predictions, demonstrating that contemporary populations have indeed evolved under these constraints. Our results provide a basis for using relatively feasible trait measurements to predict the adaptive capacity of diverse arthropod populations to geographic temperature gradients, as well as ongoing and future climatic warming.

Unexpected behavioural adaptation of yellow fever mosquitoes in response to high temperatures

Temperature is a major ecological driver of mosquito-borne diseases as it influences the life-history of both the mosquito and the pathogen harboured within it. Understanding the mosquitoes' thermal biology is essential to inform risk prediction models of such diseases. Mosquitoes can respond to temperatures by microhabitat selection through thermal preference. However, it has not yet been considered that mosquitoes are likely to adapt to changing temperatures, for example during climate change, and alter their preference over evolutionary time. We investigated this by rearing six cohorts of the yellow fever mosquito Aedes aegypti at two temperatures (24 °C, 30 °C) for 20 generations and used these cohorts to explicitly separate the effects of long-term evolution and within-generation acclimation on their thermal preferences in a thermal gradient of 20-35 °C. We found that warm-evolved mosquitoes spent 31.5% less time at high temperatures, which affects their efficiency as a vector. This study reveals the complex interplay of experimental evolution, rearing temperatures, and thermal preference in Ae. aegypti mosquitoes. It highlights the significance of incorporating mosquito microhabitat selection in disease transmission models, especially in the context of climate change.

Ocean climate and hydrodynamics drive decadal shifts in Northeast Atlantic dinoflagellates

The abundance of large marine dinoflagellates has declined in the North Sea since 1958. Although hypotheses have been proposed to explain this diminution (increasing temperature and wind), the mechanisms behind this pattern have thus far remained elusive. In this article, we study the long-term changes in dinoflagellate biomass and biodiversity in relation to hydro-climatic conditions and circulation within the North Atlantic. Our results show that the decline in biomass has paralleled an increase in biodiversity caused by a temperature-induced northward movement of subtropical taxa along the European shelf-edge, and facilitated by changes in oceanic circulation (subpolar gyre contraction). However, major changes in North Atlantic hydrodynamics in the 2010s (subpolar gyre expansion and low-salinity anomaly) stopped this movement, which triggered a biodiversity collapse in the North Sea. Further, North Sea dinoflagellate biomass remained low because of warming. Our results, therefore, reveal that regional climate warming and changes in oceanic circulation strongly influenced shifts in dinoflagellate biomass and biodiversity.

Fitness under high temperatures is overestimated when daily thermal fluctuation is ignored

Experimental studies on the thermal biology of organisms have become crucial to investigate the impact of climate warming. However, most laboratory studies are carried out under constant temperatures and assume a negligible effect from daily fluctuating temperatures. We tested this assumption on multiple fitness traits of the moth Spodoptera littoralis, and a literature review on insects complements this study. Tests on S. littoralis focused on its optimal and maximal critical temperatures by comparing constant and daily fluctuating temperatures (±5 °C) at mean temperatures of 25, 29 and 33 °C. The nine fitness parameters investigated were influenced by mean temperature. The overall effect was a maximal multiplication rate at 29 °C and a marked decrease under the fluctuating regime at 33 °C. Effects of fluctuating temperatures differed between mean temperatures. Developmental and larval survival rates at 33 °C were lower under the fluctuating thermal regime than under a constant temperature. Our literature review also illustrates that ignoring daily fluctuations based on constant temperatures commonly leads to overestimate fitness traits at high temperatures. Overlooking the experimental bias associated with constant temperatures minimizes the expected impact of climate warming on fitness traits.

Thermal preference of Culicoides biting midges in laboratory and semi-field settings

Biting midges of the genus Culicoides (Diptera: Ceratopogonidae) are hematophagous insects, and some species can transmit a plethora of pathogens, e.g., bluetongue virus and African horse sickness virus, that mainly affect animals. The transmission of vector-borne pathogens is strongly temperature dependent, and recent studies pointed to the importance of including microclimatic data when modelling disease spread. However, little is known about the preferred temperature of biting midges. The present study addressed the thermal selection of field-caught Culicoides with two experiments. In a laboratory setup, sugar-fed or blood-fed midges were video tracked for 15 min while moving inside a 60 × 30 × 4 cm setup with a 15-25 °C temperature gradient. Culicoides spent over double the time in the coldest zone of the setup compared to the warmest one. This cold selection was significantly stronger for sugar-fed individuals. Calculated preferred temperatures were 18.3 °C and 18.9 °C for sugar-fed and blood-fed Culicoides, respectively. The effect of temperature on walking speed was significant but weak, indicating that their skewed distribution results from preference and not cold trapping. A second experiment consisted of a two-way-choice-setup, performed in a 90 × 45 × 45 cm net cage, placed outdoors in a sheltered environment. Two UV LED CDC traps were placed inside the setup, and a mean temperature difference of 2.2 °C was created between the two traps. Hundred-fifty Culicoides were released per experiment. Recapture rates were negatively correlated with ambient temperature and were on average three times higher in the cooled trap. The higher prevalence of biting midges in cooler environments influences fitness and ability to transmit pathogens and should be considered in models that predict Culicoides disease transmission.

Dust storms increase the tolerance of phytoplankton to thermal and pH changes

Aquatic communities are increasingly subjected to multiple stressors through global change, including warming, pH shifts, and elevated nutrient concentrations. These stressors often surpass species tolerance range, leading to unpredictable consequences for aquatic communities and ecosystem functioning. Phytoplankton, as the foundation of the aquatic food web, play a crucial role in controlling water quality and the transfer of nutrients and energy to higher trophic levels. Despite the significance in understanding the effect of multiple stressors, further research is required to explore the combined impact of multiple stressors on phytoplankton. In this study, we used a combination of crossed experiment and mechanistic model to analyze the ecological and biogeochemical effects of global change on aquatic ecosystems and to forecast phytoplankton dynamics. We examined the effect of dust (0-75 mg L-1 ), temperature (19-27°C), and pH (6.3-7.3) on the growth rate of the algal species Scenedesmus obliquus. Furthermore, we carried out a geospatial analysis to identify regions of the planet where aquatic systems could be most affected by atmospheric dust deposition. Our mechanistic model and our empirical data show that dust exerts a positive effect on phytoplankton growth rate, broadening its thermal and pH tolerance range. Finally, our geospatial analysis identifies several high-risk areas including the highlands of the Tibetan Plateau, western United States, South America, central and southern Africa, central Australia as well as the Mediterranean region where dust-induced changes are expected to have the greatest impacts. Overall, our study shows that increasing dust storms associated with a more arid climate and land degradation can reverse the negative effects of high temperatures and low pH on phytoplankton growth, affecting the biogeochemistry of aquatic ecosystems and their role in the cycles of the elements and tolerance to global change.

Oyster larvae used for ecosystem restoration benefit from increased thermal fluctuation

A bottleneck in restoring self-sustaining beds of the European oyster (Ostrea edulis) is the successful development and settlement of larvae to bottom habitats. These processes are largely governed by temperature but a mechanistic understanding of larval performance across ecologically relevant temperatures is lacking. We reared larvae at low (20-21 °C) and high (20-24 °C) fluctuating temperatures and applied short-term exposures of larvae to temperatures between 16 and 33 °C to assess vital rates and thermal coping ranges. Larval thermal preference was between 25 and 30 °C for both rearing treatments which corresponded with optimum temperatures for oxygen consumption rates and locomotion. Larvae had 5.5-fold higher settling success, however, when reared at the high compared to the low fluctuating temperatures. Higher mean and periods of increased temperature, as projected in a future climate, may therefore enhance recruitment success of O. edulis in northern European habitats.

Terrestrial amphibians respond to rapidly changing temperatures with individual plasticity of exploratory behaviour

Terrestrial ectotherms react to acute changes in environmental temperatures by adjusting their behaviour. Evaluating the adaptive potential of these behavioural adjustments requires information on their repeatability and plasticity. We examined behavioural response (exploration) to acute temperature change in two amphibian taxa, alpine (Ichthyosaura alpestris) and smooth (Lissotriton vulgaris) newts. These responses were investigated at both population and individual levels under multiple thermal contexts (dimensions), represented by the direction and range of changing temperature and rearing thermal regimes. Population-level analyses showed species-specific, non-additive effects of direction and range of temperature change on acute thermal reaction norms for exploration, but explained only a low amount (7-23%) of total variation in exploration. In contrast, within- and among-individual variation in acute thermal reaction norm parameters explained 42-50% of total variation in the examined trait. Although immediate thermal responses varied among individuals (repeatability = 0.07 to 0.53), they were largely shaped by environmental contexts during repeated trials. We conclude that these amphibians respond to acute temperature change through individual plasticity of behavioural traits. A repeated-measures approach under multiple thermal contexts will be needed to identify the selective and plastic potential of behavioural responses used by juvenile newts and perhaps other ectotherm taxa to cope with rapidly changing environmental temperatures.

Effects of temperature on metabolic rate during metamorphosis in the alfalfa leafcutting bee

Spring conditions, especially in temperate regions, may fluctuate abruptly and drastically. Environmental variability can expose organisms to temperatures outside of their optimal thermal ranges. For ectotherms, sudden changes in temperature may cause short- and long-term physiological effects, including changes in respiration, morphology, and reproduction. Exposure to variable temperatures during active development, which is likely to occur for insects developing in spring, can cause detrimental effects. Using the alfalfa leafcutting bee, Megachile rotundata, we aimed to determine if oxygen consumption could be measured using a new system and to test the hypothesis that female and male M. rotundata have a thermal performance curve with a wide optimal range. Oxygen consumption of M. rotundata pupae was measured across a large range of temperatures (6-48°C) using an optical oxygen sensor in a closed respirometry system. Absolute and mass-specific metabolic rates were calculated and compared between bees that were extracted from their brood cells and those remaining in the brood cell to determine whether pupae could be accurately measured inside their brood cells. The metabolic response to temperature was non-linear, which is an assumption of a thermal performance curve; however, the predicted negative slope at higher temperatures was not observed. Despite sexual dimorphism in body mass, sex differences only occurred in mass-specific metabolic rates. Higher metabolic rates in males may be attributed to faster development times, which could explain why there were no differences in absolute metabolic rate measurements. Understanding the physiological and ecological effects of thermal environmental variability on M. rotundata will help to better predict their response to climate change.

Temperate species underfill their tropical thermal potentials on land

Understanding how temperature determines the distribution of life is necessary to assess species' sensitivities to contemporary climate change. Here, we test the importance of temperature in limiting the geographic ranges of ectotherms by comparing the temperatures and areas that species occupy to the temperatures and areas species could potentially occupy on the basis of their physiological thermal tolerances. We find that marine species across all latitudes and terrestrial species from the tropics occupy temperatures that closely match their thermal tolerances. However, terrestrial species from temperate and polar latitudes are absent from warm, thermally tolerable areas that they could potentially occupy beyond their equatorward range limits, indicating that extreme temperature is often not the factor limiting their distributions at lower latitudes. This matches predictions from the hypothesis that adaptation to cold environments that facilitates survival in temperate and polar regions is associated with a performance trade-off that reduces species' abilities to contend in the tropics, possibly due to biotic exclusion. Our findings predict more direct responses to climate warming of marine ranges and cool range edges of terrestrial species.

Aerobic metabolic scope mapping of an invasive fish species with global warming

Climate change will exacerbate the negative effects associated with the introduction of non-indigenous species in marine ecosystems. Predicting the spread of invasive species in relation to environmental warming is therefore a fundamental task in ecology and conservation. The Baltic Sea is currently threatened by several local stressors and the highest increase in sea surface temperature of the world's large marine ecosystems. These new thermal conditions can further favour the spreading of the invasive round goby (Neogobius melanostomus), a fish of Ponto-Caspian origin, currently well established in the southern and central parts of the Baltic Sea. This study aims to assess the thermal habitat suitability of the round goby in the Baltic Sea considering the past and future conditions. The study combines sightings records with known physiological models of aerobic performance and sea surface temperatures. Physiological models read these temperatures, at sighting times and locations, to determine their effects on the aerobic metabolic scope (AMS) of the fish, a measure of its energetic potential in relation to environmental conditions. The geographical mapping of the AMS was used to describe the changes in habitat suitability during the past 3 decades and for climatic predictions (until 2100) showing that the favourable thermal habitat in the Baltic Sea has increased during the past 32 years and will continue to do so in all the applied climate model predictions. Particularly, the predicted new thermal conditions do not cause any reduction in the AMS of round goby populations, while the wintertime cold ranges are likely expected to preserve substantial areas from invasion. The results of this research can guide future monitoring programs increasing the chance to detect this invader in novel areas.

Cool shade and not-so-cool shade: How habitat loss may accelerate thermal stress under current and future climate

Worldwide habitat loss, land-use changes, and climate change threaten biodiversity, and we urgently need models that predict the combined impacts of these threats on organisms. Current models, however, overlook microhabitat diversity within landscapes and so do not accurately inform conservation efforts, particularly for ectotherms. Here, we built and field-parameterized a model to examine the effects of habitat loss and climate change on activity and microhabitat selection by a diurnal desert lizard. Our model predicted that lizards in rock-free areas would reduce summer activity levels (e.g. foraging, basking) and that future warming will gradually decrease summer activity in rocky areas, as even large rocks become thermally stressful. Warmer winters will enable more activity but will require bushes and small rocks as shade retreats. Hence, microhabitats that may seem unimportant today will become important under climate change. Modelling frameworks should consider the microhabitat requirements of organisms to improve conservation outcomes.

Preferred temperature in the warmth of cities: Body size, sex and development stage matter more than urban climate in a ground-dwelling spider

Most ectotherms rely on behavioural thermoregulation to maintain body temperatures close to their physiological optimum. Hence, ectotherms can drastically limit their exposure to thermal extremes by selecting a narrower range of temperatures, which includes their preferred temperature (Tpref). Despite evidence that behavioural thermoregulation can be adjusted by phenotypic plasticity or constrained by natural selection, intraspecific Tpref variations across environmental gradients remain overlooked as compared to other thermal traits like thermal tolerance. Here, we analyzed Tpref variation of spider populations found along a gradient of urban heat island (UHI) which displays large thermal variations over small distances. We measured two components of the thermal preference, namely the mean Tpref and the Tpref range (i.e., standard deviation) in 557 field-collected individuals of a common ground-dwelling spider (Pardosa saltans, Lycosidae) using a laboratory thermal gradient. We determined if Tpref values differed among ten populations from contrasting thermal zones. We showed that endogenous factors such as body size or sex primarily determine both mean Tpref and Tpref range. The Tpref range was also linked to the UHI intensity to a lesser extent, yet only in juveniles. The absence of relationship between Tpref metrics and UHI in adult spiders suggests a Bogert effect according to which the ability of individuals to detect and exploit optimal microclimates weakens the selection pressure of temperatures (here driven by UHI) on their thermal physiology. Alternatively, this lack of relationship could also indicate that temperature patterns occurring at the scale of the spiders' micro-habitat differ from measured ones. This study shows the importance of considering both inter-individual and inter-population variations of the Tpref range when conducting Tpref experiments, and supports Tpref range as being a relevant measure to inform on the strength of behavioural thermoregulation in a given population.

Thermal preference of adult mosquitoes (Culicidae) and biting midges (Ceratopogonidae) at different altitudes in Switzerland

Mosquitoes (Diptera: Culicidae) and biting midges (Diptera: Ceratopogonidae) are among the most important vectors of human and veterinary pathogens. For modelling the distribution of these pathogens, entomological aspects are essential, which in turn are highly dependent on environmental factors, such as temperature. In this study, mosquitoes and biting midges were sampled in multiple microclimates at two low (360, 480 meters above sea level, m.a.s.l.) and two high (1250, 1530 m.a.s.l.) altitude locations in Switzerland. Sets of various traps (CO2 -baited CDC, LED-UV, resting boxes, oviposition cups) equipped with dataloggers were placed in transects at five sites with similar vegetation at each location. Only the CDC and the LED-UV traps collected enough insects for analyses. Taxonomic diversity was greater for mosquitoes but lower for biting midges at lower altitudes. Both mosquitoes and biting midges had a thermal preference. Culicoides preferred the traps with warmer microclimate, especially at lower altitudes, whereas mosquito preferences depended on the species, but not on altitude. Relative humidity had a significant positive impact on catches of biting midges but not mosquitoes. To obtain better data on thermal preferences of resting and ovipositing vectors in addition to host seeking individuals, new and improved collecting methods are needed.

Short-term temperature fluctuations increase disease in a Daphnia-parasite infectious disease system

Climate change has profound effects on infectious disease dynamics, yet the impacts of increased short-term temperature fluctuations on disease spread remain poorly understood. We empirically tested the theoretical prediction that short-term thermal fluctuations suppress endemic infection prevalence at the pathogen's thermal optimum. This prediction follows from a mechanistic disease transmission model analyzed using stochastic simulations of the model parameterized with thermal performance curves (TPCs) from metabolic scaling theory and using nonlinear averaging, which predicts ecological outcomes consistent with Jensen's inequality (i.e., reduced performance around concave-down portions of a thermal response curve). Experimental observations of replicated epidemics of the microparasite Ordospora colligata in Daphnia magna populations indicate that temperature variability had the opposite effect of our theoretical predictions and instead increase endemic infection prevalence. This positive effect of temperature variability is qualitatively consistent with a published hypothesis that parasites may acclimate more rapidly to fluctuating temperatures than their hosts; however, incorporating hypothetical effects of delayed host acclimation into the mechanistic transmission model did not fully account for the observed pattern. The experimental data indicate that shifts in the distribution of infection burden underlie the positive effect of temperature fluctuations on endemic prevalence. The increase in disease risk associated with climate fluctuations may therefore result from disease processes interacting across scales, particularly within-host dynamics, that are not captured by combining standard transmission models with metabolic scaling theory.

Climate change is not just global warming: Multidimensional impacts on animal gut microbiota

Climate change has rapidly altered many ecosystems, with detrimental effects for biodiversity across the globe. In recent years, it has become increasingly apparent that the microorganisms that live in and on animals can substantially affect host health and physiology, and the structure and function of these microbial communities can be highly sensitive to environmental variables. To date, most studies have focused on the effects of increasing mean temperature on gut microbiota, yet other aspects of climate are also shifting, including temperature variation, seasonal dynamics, precipitation and the frequency of severe weather events. This array of environmental pressures might interact in complex and non-intuitive ways to impact gut microbiota and consequently alter animal fitness. Therefore, understanding the impacts of climate change on animals requires a consideration of multiple types of environmental stressors and their interactive effects on gut microbiota. Here, we present an overview of some of the major findings in research on climatic effects on microbial communities in the animal gut. Although ample evidence has now accumulated that shifts in mean temperature can have important effects on gut microbiota and their hosts, much less work has been conducted on the effects of other climatic variables and their interactions. We provide recommendations for additional research needed to mechanistically link climate change with shifts in animal gut microbiota and host fitness.

Phenological mismatch affects individual fitness and population growth in the winter moth

Climate change can severely impact species that depend on temporary resources by inducing phenological mismatches between consumer and resource seasonal timing. In the winter moth, warmer winters caused eggs to hatch before their food source, young oak leaves, became available. This phenological mismatch changed the selection on the temperature sensitivity of egg development rate. However, we know little about the fine-scale fitness consequences of phenological mismatch at the individual level and how this mismatch affects population dynamics in the winter moth. To determine the fitness consequences of mistimed egg hatching relative to timing of oak budburst, we quantified survival and pupation weight in a feeding experiment. We found that mismatch greatly increased mortality rates of freshly hatched caterpillars, as well as affecting caterpillar growth and development time. We then investigated whether these individual fitness consequences have population-level impacts by estimating the effect of phenological mismatch on population dynamics, using our long-term data (1994-2021) on relative winter moth population densities at four locations in The Netherlands. We found a significant effect of mismatch on population density with higher population growth rates in years with a smaller phenological mismatch. Our results indicate that climate change-induced phenological mismatch can incur severe individual fitness consequences that can impact population density in the wild.

Weak sex-specific evolution of locomotor activity of Sepsis punctum (Diptera: Sepsidae) thermal experimental evolution lines

Elevated temperatures are expected to rise beyond what the physiology of many organisms can tolerate. Behavioural responses facilitating microhabitat shifts may mitigate some of this increased thermal selection on physiology, but behaviours are themselves mediated by physiology, and any behavioural response may trade-off against other fitness-related activities. We investigated whether experimental evolution in different thermal regimes (Cold: 15 °C; Hot: 31 °C; Intergenerational fluctuation 15/31 °C; Control: 23 °C) resulted in genetic differentiation of standard locomotor activity in the dung fly Sepsis punctum. We assessed individual locomotor performance, an integral part of most behavioral repertoires, across eight warm temperatures from 24 °C to 45 °C using an automated device. We found no evidence for generalist-specialist trade-offs (i.e. changes in the breadth of the performance curve) for this trait. Instead, at the warmest assay temperatures hot-selected flies showed somewhat higher maximal performance than all other, especially cold-selected flies, overall more so in males than females. Yet, the flies' temperature optimum was not higher than that of the cold-selected flies, as expected under the 'hotter-is-better' hypothesis. Maximal locomotor performance merely weakly increased with body size. These results suggest that thermal performance curves are unlikely to evolve as an entity according to theory, and that locomotor activity is a trait of limited use in revealing thermal adaptation.

Phytoplankton life strategies, phenological shifts and climate change in the North Atlantic Ocean from 1850 to 2100

Significant phenological shifts induced by climate change are projected within the phytoplankton community. However, projections from current Earth System Models (ESMs) understandably rely on simplified community responses that do not consider evolutionary strategies manifested as various phenotypes and trait groups. Here, we use a species-based modelling approach, combined with large-scale plankton observations, to investigate past, contemporary and future phenological shifts in diatoms (grouped by their morphological traits) and dinoflagellates in three key areas of the North Atlantic Ocean (North Sea, North-East Atlantic and Labrador Sea) from 1850 to 2100. Our study reveals that the three phytoplanktonic groups exhibit coherent and different shifts in phenology and abundance throughout the North Atlantic Ocean. The seasonal duration of large flattened (i.e. oblate) diatoms is predicted to shrink and their abundance to decline, whereas the phenology of slow-sinking elongated (i.e. prolate) diatoms and of dinoflagellates is expected to expand and their abundance to rise, which may alter carbon export in this important sink region. The increase in prolates and dinoflagellates, two groups currently not considered in ESMs, may alleviate the negative influence of global climate change on oblates, which are responsible of massive peaks of biomass and carbon export in spring. We suggest that including prolates and dinoflagellates in models may improve our understanding of the influence of global climate change on the biological carbon cycle in the oceans.

Seasonal specialization drives divergent population dynamics in two closely related butterflies

Seasons impose different selection pressures on organisms through contrasting environmental conditions. How such seasonal evolutionary conflict is resolved in organisms whose lives span across seasons remains underexplored. Through field experiments, laboratory work, and citizen science data analyses, we investigate this question using two closely related butterflies (Pieris rapae and P. napi). Superficially, the two butterflies appear highly ecologically similar. Yet, the citizen science data reveal that their fitness is partitioned differently across seasons. Pieris rapae have higher population growth during the summer season but lower overwintering success than do P. napi. We show that these differences correspond to the physiology and behavior of the butterflies. Pieris rapae outperform P. napi at high temperatures in several growth season traits, reflected in microclimate choice by ovipositing wild females. Instead, P. rapae have higher winter mortality than do P. napi. We conclude that the difference in population dynamics between the two butterflies is driven by seasonal specialization, manifested as strategies that maximize gains during growth seasons and minimize harm during adverse seasons, respectively.

Temperature preference of sugar- or blood-fed Aedes japonicus mosquitoes under semi-natural conditions

Mosquito-borne diseases pose a major burden on humans and animals. Temperature strongly influences the physiology and life cycle of mosquitoes and also the pathogens they transmit. Thermoregulatory behaviour of mosquitoes has been addressed in a few laboratory studies. Here, we expand such studies by investigating the thermal preference when resting of Aedes japonicus, an invasive and putative vector species of many pathogens, in a semi-field setup during summers in a temperate climate. Blood-fed or sugar-fed Ae. japonicus females were released in the late afternoon in a large outdoor cage containing three resting boxes. The next morning, temperature treatments were applied to the boxes, creating a "cool" (over all experiments around 18 °C), and a "warm" (around 35 °C) microhabitat in addition to an untreated "ambient" (around 26 °C) one. The mosquitoes resting within the three boxes were counted five times, every 2 h between 9h and 17h. The highest proportions of mosquitoes (e.g. up to 21% of blood-fed ones) were found in the cool box while both blood-fed and sugar-fed mosquitoes avoided the warm box. The mean resting temperatures of Ae. japonicus were below the ambient temperatures measured by a nearby meteorological station, and this was more pronounced at higher outdoor temperatures and in blood-fed as compared to sugar-fed mosquitoes. Thus, over all experiments with blood-fed mosquitoes, the calculated average resting temperature was 4 °C below the outdoor temperature. As mosquitoes prefer cooler resting places than temperatures measured by weather stations in summer, models to predict mosquito-borne disease outbreaks need to account for the thermoregulatory behaviour of mosquitoes, especially in the wake of climate change.

Mortality, metabolic rate, and oviposition of Gryllus (Gryllus) assimilis (Fabricius, 1775) (Orthoptera: Gryllidae) females under constant and fluctuating warm temperatures

The global average temperature will increase by up to 5.7 °C, under high greenhouse gas emissions, consequently increasing the frequency of heatwaves, according to recent IPCC forecasts. These especially impacts ectotherms, such as insects, which are the most susceptible animals to changes in environmental temperature, affecting their physiology and reproduction. Thus, we investigated the effects of a 96-h exposure to constant temperatures (CT: 27, 30.5, 34, 39, 41, or 43 °C) and fluctuating temperatures (FT: 27/34 °C, 12/12 h) on the survival, metabolic rate, and oviposition of the female cricket Gryllus (Gryllus) assimilis (Orthoptera: Gryllidae). Mortality, body mass and water content of females and males were quantified and compared. It was found that CT₂₇, CT₃₄ and FT_27/34 do not cause mortality in females of G. (G.) assimilis. CT_30.5 (average temperature between 27 and 34), despite causing mortality of 5.0 ± 3.5%, do not differ from CT₂₇, CT₃₄ or FT_27/34. CT₃₉ causes a mortality of 8.3 ± 5.5%. Estimated lethal temperature for 50% of the population of females (LT_50Temp) is 40 °C, and 43 °C promotes 100% mortality in 96 h. Comparing mortality between sexes, females present higher LT_50Temp and thermotolerance than males. In addition, FT_27/34 and CT₃₄ do not differ in the metabolic rate, but both have higher values than CT₂₇. CT₃₄ strongly reduces oviposition in females, however FT_27/34 does not. We suggest that CT₃₄ reduces oviposition in females in two ways: by affecting the endocrine system related to egg production, or by causing behavioral egg retention, as a strategy to survive thermal stress. Moreover, females had a higher wet body mass and present a lower average weight loss than males. In conclusion, despite females present a higher mortality at temperatures above 39 °C, they are more thermotolerant than males. Furthermore, CT₃₄ is detrimental to the oviposition of G. (G.) assimilis.

Impacts of rising temperatures and water acidification on the oxidative status and immune system of aquatic ectothermic vertebrates: A meta-analysis

Species persistence in the Anthropocene is dramatically threatened by global climate change. Large emissions of carbon dioxide (CO₂) from human activities are driving increases in mean temperature, intensity of heatwaves, and acidification of oceans and freshwater bodies. Ectotherms are particularly sensitive to CO₂-induced stressors, because the rate of their metabolic reactions, as well as their immunological performance, are affected by environmental temperatures and water pH. We reviewed and performed a meta-analysis of 56 studies, involving 1259 effect sizes, that compared oxidative status or immune function metrics between 42 species of ectothermic vertebrates exposed to long-term increased temperatures or water acidification (≥48 h), and those exposed to control parameters resembling natural conditions. We found that CO₂-induced stressors enhance levels of molecular oxidative damages in ectotherms, while the activity of antioxidant enzymes was upregulated only at higher temperatures, possibly due to an increased rate of biochemical reactions dependent on the higher ambient temperature. Differently, both temperature and water acidification showed weak impacts on immune function, indicating different direction (increase or decrease) of responses among immune traits. Further, we found that the intensity of temperature treatments (Δ°C) and their duration, enhance the physiological response of ectotherms, pointing to stronger effects of prolonged extreme warming events (i.e., heatwaves) on the oxidative status. Finally, adult individuals showed weaker antioxidant enzymatic responses to an increase in water temperature compared to early life stages, suggesting lower acclimation capacity. Antarctic species showed weaker antioxidant response compared to temperate and tropical species, but level of uncertainty in the antioxidant enzymatic response of Antarctic species was high, thus pairwise comparisons were statistically non-significant. Overall, the results of this meta-analysis indicate that the regulation of oxidative status might be one key mechanism underlying thermal plasticity in aquatic ectothermic vertebrates.

Climate drives global functional trait variation in lizards

A major challenge in ecology and evolution is to disentangle the mechanisms driving broad-scale variation in biological traits such as body size, colour, thermal physiology traits and behaviour. Climate has long been thought to drive trait evolution and abiotic filtering of trait variation in ectotherms because their thermal performance and fitness are closely related to environmental conditions. However, previous studies investigating climatic variables associated with trait variation have lacked a mechanistic description of the underpinning processes. Here, we use a mechanistic model to predict how climate affects thermal performance of ectotherms and thereby the direction and strength of the effect of selection on different functional traits. We show that climate drives macro-evolutionary patterns in body size, cold tolerance and preferred body temperatures among lizards, and that trait variation is more constrained in regions where selection is predicted to be stronger. These findings provide a mechanistic explanation for observations on how climate drives trait variation in ectotherms through its effect on thermal performance. By connecting physical, physiological and macro-evolutionary principles, the model and results provide an integrative, mechanistic framework for predicting organismal responses to present climates and climate change.

Trade-off between thermal preference and sperm maturation in a montane lizard

Temperature is a key abiotic factor that influences performance of several physiological traits in ectotherms. Organisms regulate their body temperature within a range of temperatures to enhance physiological function. The capacity of ectotherms, such as lizards, to maintain their body temperature within their preferred range influences physiological traits such as speed, various reproductive patterns, and critical fitness components, such as growth rates or survival. Here, we evaluate the influence of temperature on locomotor performance, sperm morphology and viability in a high elevation lizard species (Sceloporus aeneus). Whereas maximal values for sprint speed coincides with field active and preferred body temperature, short-term exposure at the same range of temperatures produces abnormalities in sperm morphology, lower sperm concentration and diminishes sperm motility and viability. In conclusion, we confirmed that although locomotor performance is maximized at preferred temperatures, there is a trade-off with male reproductive attributes, which may cause infertility. As a consequence, prolonged exposure to preferred temperatures could threaten the persistence of the species through reduced fertility. Persistence of the species is favored in environments with access to cooler, thermal microhabitats that enhance reproductive parameters.

Spatiotemporal thermal variation drives diversity trends in experimental landscapes

Temperature is a fundamental driver of species' vital rates and thus coexistence, extinctions and community composition. While temperature is neither static in space nor in time, little work has incorporated spatiotemporal dynamics into community-level investigations of thermal variation. We conducted a microcosm experiment using ciliate protozoa to test the effects of temperatures fluctuating synchronously or asynchronously on communities in two-patch landscapes connected by short or long corridors. We monitored the abundance of each species for 4 weeks-equivalent to ~28 generations-measuring the effects of four temperature regimes and two corridor lengths on community diversity and composition. While corridor length significantly altered the trajectory of diversity change in the communities, this did not result in different community structures at the end of the experiment. The type of thermal variation significantly affected both the temporal dynamics of diversity change and final community composition, with synchronous fluctuation causing deterministic extinctions that were consistent across replicates and spatial variation causing the greatest diversity declines. Our results suggest that the presence and type of thermal variation can play an important role in structuring ecological communities, especially when it interacts with dispersal between habitat patches.

The potential climatic range of spotted lanternfly may be broader than previously predicted

Spotted lanternfly (Lycorma delicatula White) is an invasive planthopper that was introduced to the United States from Asia and readily spreads via human aided means. Three geographically separated populations in the United States (NJ, PA, and WV) were collected and used to assess the effects of fluctuating thermal regimes that included temperatures above or below the upper (Tmax) and lower (Tmin) developmental thresholds, respectively, on nymphal survival and development, and to determine if there was within- and among-population variation in hatch timing and temperature responses of nymphs. Nymphs exposed to temperatures > Tmax and Collapse

Key Words

• climate
• development
• phenology
• survival
• temperature

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MESH Headings Collapse

Grants

• Animal and Plant Health Inspection Service
• Northern Research Station

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Affiliation(s)

Melody A. Keena Northern Research Station, United States Department of Agriculture (USDA) Forest Service, Hamden, CT, United States
George Hamilton Department of Entomology, Rutgers, The State University of New Jersey, New Brunswick, NJ, United States
Devin Kreitman Department of Entomology, Rutgers, The State University of New Jersey, New Brunswick, NJ, United States

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Highly conserved thermal performance strategies may limit adaptive potential in corals

Increasing seawater temperatures are expected to have profound consequences for reef-building corals' physiology. Understanding how demography changes in response to chronic exposure to warming will help forecast how coral communities will respond to climate change. Here, we measure growth rates of coral fragments of four common species, while exposing them to temperatures ranging from 19°C to 31°C for one month to calibrate their thermal-performance curves (TPCs). Our results show that, while there are contrasting differences between species, the shape of the TPCs was remarkably consistent among individuals of the same species. The low variation in thermal sensitivity within species may imply a reduced capacity for rapid adaptive responses to future changes in thermal regimes. Additionally, interspecific differences in thermal responses show a negative relationship between maximum growth and thermal optima, contradicting expectations derived from the classic 'warmer-is-better' hypothesis. Among species, there was a trade-off between current and future growth, whereby most species perform well under current thermal regimes but are susceptible to future increases in temperature. Increases in water temperature with climate change are likely to reduce growth rates, further hampering future coral reef recovery rates and potentially altering community composition.

Developmental Differentiations of Major Maize Stemborers Due to Global Warming in Temperate and Tropical Climates

While many insects are in decline due to global warming, the effect of rising temperatures on crop insect pests is uncertain. A capacity to understand future changes in crop pest populations remains critical to ensure food security. Using temperature-dependent mathematical models of the development of four maize stemborers in temperate and tropical regions, we evaluated the potential impacts of different climate change scenarios on development time. While recognizing the limitations of the temperature-dependent development rate approach, we found that global warming could either be beneficial or detrimental to pest development, depending on the optimal temperature for the development of the species and scenarios of climate change. Expected responses range from null development to 1.5 times faster development than expected today. These results suggest that in the medium term, the studied species could benefit from global warming with an accelerated development, while in the long term, their development could either be delayed or accelerated, which may impact their dynamics with implications on maize cultivation.

Behavioural adaptation to heat stress: Shell lifting of the hermit crab Diogenes deflectomanus

Behavioural responses to heat and desiccation stress in ectotherms are crucial for their survival in habitats where environmental temperatures are close to or even exceed their upper thermal limits. During low tide periods when pools in intertidal sediments heat up, a novel shell lifting behaviour (when hermit crabs crawl out of pools and lift up their shells) was observed in the hermit crab, Diogenes deflectomanus, on tropical sandy shores. On-shore measurements revealed that the hermit crabs left pools and lifted their shells predominantly when pool water exceeded 35.4 °C. Standing on emersed substrates above the pool water, the hermit crabs maintained their body temperatures at 26 - 29 °C, ∼ 10 °C lower than temperatures at which their physiological performances (as measured using heart rate) reached the maximum. This mismatch between preferred body temperatures and temperatures at maximal physiological performance was also observed under a laboratory controlled thermal gradient, where hermit crabs spent more time at 22 - 26 °C as compared to > 30 °C. These behaviours suggest a thermoregulatory function of the shell lifting behaviour, where the hermit crabs can avoid further increase in body temperatures when pools heat up during low tide periods. Such a behavioural decision allows the hermit crabs to be less prone to the strong temporal fluctuation in temperatures experienced during emersion periods on thermally dynamic tropical sandy shores.

Geothermal stickleback populations prefer cool water despite multigenerational exposure to a warm environment

Given the threat of climate change to biodiversity, a growing number of studies are investigating the potential for organisms to adapt to rising temperatures. Earlier work has predicted that physiological adaptation to climate change will be accompanied by a shift in temperature preferences, but empirical evidence for this is lacking. Here, we test whether exposure to different thermal environments has led to changes in preferred temperatures in the wild. Our study takes advantage of a "natural experiment" in Iceland, where freshwater populations of threespine sticklebacks (Gasterosteus aculeatus) are found in waters warmed by geothermal activity year-round (warm habitats), adjacent to populations in ambient-temperature lakes (cold habitats). We used a shuttle-box approach to measure temperature preferences of wild-caught sticklebacks from three warm-cold population pairs. Our prediction was that fish from warm habitats would prefer higher water temperatures than those from cold habitats. We found no support for this, as fish from both warm and cold habitats had an average preferred temperature of 13°C. Thus, our results challenge the assumption that there will be a shift in ectotherm temperature preferences in response to climate change. In addition, since warm-habitat fish can persist at relatively high temperatures despite a lower-temperature preference, we suggest that preferred temperature alone may be a poor indicator of a population's adaptive potential to a novel thermal environment.