Thermal performance under constant temperatures can accurately predict insect development times across naturally variable microclimates

Comparative life-history responses of lacewings to changes in temperature

Insects play a crucial role in all ecosystems, and are increasingly exposed to higher in temperature extremes under climate change, which can have substantial effects on their abundances. However, the effects of temperature on changes in abundances or population fitness are filtered through differential responses of life-history components, such as survival, reproduction, and development, to their environment. Such differential responses, or trade-offs, have been widely studied in birds and mammals, but comparative studies on insects are largely lacking, limiting our understanding of key mechanisms that may buffer or exacerbate climate-change effects across insect species. Here, we performed a systematic literature review of the ecological studies of lacewings (Neuroptera), predatory insects that play a crucial role in ecosystem pest regulation, to investigate the impact of temperature on life cycle dynamics across species. We found quantitative information, linking stage-specific survival, development, and reproduction to temperature variation, for 62 species from 39 locations. We then performed a metanalysis calculating sensitives to temperature across life-history processes for all publications. We found that developmental times consistently decreased with temperature for all species. Survival and reproduction however showed a weaker response to temperature, and temperature sensitivities varied substantially among species. After controlling for the effect of temperature on life-history processes, the latter covaried consistently across two main axes of variation related to instar and pupae development, suggesting the presence of life-history trade-offs. Our work provides new information that can help generalize life-history responses of insects to temperature, which can then expand comparative demographic and climate-change research. We also discuss important remaining knowledge gaps, such as a better assessment of adult survival and diapause.

Modelling thermal reaction norms for development and viability in Drosophila suzukii under constant, fluctuating and field conditions

Phenological models for insect pests often rely on knowledge of thermal reaction norms. These may differ in shape depending on developmental thermal conditions (e.g. constant vs. fluctuating) and other factors such as life-stages. Here, we conducted an extensive comparative study of the thermal reaction norms for development and viability in the invasive fly, Drosophila suzukii, under constant and fluctuating thermal regimes. Flies, were submitted to 15 different constant temperatures (CT) ranging from 8 to 35 °C. We compared responses under CT with patterns observed under 15 different fluctuating temperature (FT) regimes. We tested several equations for thermal performance curves and compared various models to obtain thermal limits and degree-day estimations. To validate the model's predictions, the phenology was monitored in two artificial field-like conditions and two natural conditions in outdoor cages during spring and winter. Thermal reaction norm for viability from egg to pupa was broader than that from egg to adult. FT conditions yielded a broader thermal breadth for viability than CT, with a performance extended towards the colder side, consistent with our field observations in winter. Models resulting from both CT and FT conditions made accurate predictions of degree-day as long as the temperature remained within the linear part of the developmental rate curve. Under cold artificial and natural winter conditions, a model based on FT data made more accurate predictions. Model based on CT failed to predict adult's emergence in winter. We also document the first record of development and adult emergence throughout winter in D. suzukii. Population dynamics models in D. suzukii are all based on summer phenotype and CT. Accounting for variations between seasonal phenotypes, stages, and thermal conditions (CT vs. FT) could improve the predictive power of the models.

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.

Phenotypic plasticity and the effects of thermal fluctuations on specialists and generalists

Classical theories predict that relatively constant environments should generally favour specialists, while fluctuating environments should be selected for generalists. However, theoretical and empirical results have pointed out that generalist organisms might, on the contrary, perform poorly under fluctuations. In particular, if generalism is underlaid by phenotypic plasticity, performance of generalists should be modulated by the temporal characteristics of environmental fluctuations. Here, we used experiments in microcosms of Tetrahymena thermophila ciliates and a mathematical model to test whether the period or autocorrelation of thermal fluctuations mediate links between the level of generalism and the performance of organisms under fluctuations. In the experiment, thermal fluctuations consistently impeded performance compared with constant conditions. However, the intensity of this effect depended on the level of generalism: while the more specialist strains performed better under fast or negatively autocorrelated fluctuations, plastic generalists performed better under slow or positively autocorrelated fluctuations. Our model suggests that these effects of fluctuations on organisms' performance may result from a time delay in the expression of plasticity, restricting its benefits to slow enough fluctuations. This study points out the need to further investigate the temporal dynamics of phenotypic plasticity to better predict its fitness consequences under environmental fluctuations.

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.

Copper-contaminated soil compromises thermal performance in the springtail Folsomia candida (Collembola)

The widespread agricultural and industrial emissions of copper-based chemicals have increased copper levels in soils worldwide. Copper contamination can cause a range of toxic effects on soil animals and influence thermal tolerance. However, toxic effects are commonly investigated using simple endpoints (e.g., mortality) and acute tests. Thus, how organisms respond to ecological realistic sub-lethal and chronic exposures across the entire thermal scope of an organism is not known. In this study, we investigated the effects of copper exposure on the thermal performance of a springtail (Folsomia candida), regarding its survival, individual growth, population growth, and the composition of membrane phospholipid fatty acids. Folsomia candida (Collembola) is a typical representative of soil arthropods and a model organism that has been widely used for ecotoxicological studies. In a full-factorial soil microcosm experiment, springtails were exposed to three levels of copper (ca. 17 (control), 436, and 1629 mg/kg dry soil) and ten temperatures from 0 to 30 °C. Results showed that three-week copper exposure at temperatures below 15 °C and above 26 °C negatively influenced the springtail survival. The body growth was significantly lower for the springtails in high-dose copper soils at temperatures above 24 °C. A high copper level reduced the number of juveniles by 50 %, thereby impairing population growth. Both temperature and copper exposure significantly impacted membrane properties. Our results indicated that high-dose copper exposure compromised the tolerance to suboptimal temperatures and decreased maximal performance, whereas medium copper exposure partially reduced the performance at suboptimal temperatures. Overall, copper contamination reduced the thermal tolerance of springtails at suboptimal temperatures, probably by interfering with membrane homeoviscous adaptation. Our results show that soil organisms living in copper-contaminated areas might be more sensitive to thermally stressful periods.

Ecological zoning of Euschistus heros in Brazil based on the net reproductive rate at different temperatures and relative-humidity levels

The Neotropical brown stink bug, Euschistus heros (Fabricius, 1798) (Hemiptera: Pentatomidae), is one of the major insect pests in soybean crops, causing severe damage; however, some aspects of its biology that are essential for management remain unknown. To aid in the management of E. heros, the present study investigated the fertility life table of this species at 7 temperatures (18, 20, 22, 25, 28, 30, and 32 ± 1 °C) and 4 relative-humidity levels (30, 50, 70, and 90 ± 10%). Based on the net reproductive rate, R0, we developed an ecological zoning for this pest in Brazil, to identify climatically favorable areas for population growth. Our results indicated that the most favorable range is between 25 and 28 °C and above 70% RH. The ecological zoning indicated that farmers should be more concerned in the northern and Midwest regions, which include the state of Mato Grosso, the largest soybean and corn producer in Brazil. These results provide valuable information, indicating the hotspots most likely to be attacked by the Neotropical brown stink bug.

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.

Thermal Oviposition Performance of the Ladybird Stethorus gilvifrons Preying on Two-Spotted Spider Mites

The ladybird, Stethorus gilvifrons (Mulsant) (Coleoptera: Coccinellidae), is an important predator of two-spotted spider mites, Tetranychus urticae Koch (Acari: Tetranychidae), in southeastern Europe and western and southwestern Asia, such as Iran, India, and Turkey. To enhance forecasting the occurrence and performance of this predator in natural control and improve its usage in biological control, we evaluated and compared four non-linear oviposition models, i.e., Enkegaard, Analytis, Bieri-1, and Bieri-2. The models were validated by using data of age-specific fecundity of female S. gilvifrons at six constant temperatures (15, 20, 25, 27, 30, and 34 °C). All four models provided good fit quality to age-dependent oviposition at 15 to 30 °C (R² 0.67 to 0.94; R²_adj 0.63 to 0.94) but had a poor fit at 34 °C (R² 0.33 to 0.40; R²_adj 0.17 to 0.34). Within temperatures, the best performing models were Bieri-1 (R²), Bieri-2 (R²_adj), and Analytis (RSS) at 15 °C, Bieri-1 at 27 °C, and Analytis at 20, 25, and 30 °C. Analytis was the best suited model across the wide temperature range tested (from 15 to 30 °C). The models presented here allow for prediction of the population dynamics of S. gilvifrons in field and greenhouse crops in temperate and subtropical climates.

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.

Stay in shape: Assessing the adaptive potential of shell morphology and its sensitivity to temperature in the invasive New Zealand mud snail Potamopyrgus antipodarum through phenotypic plasticity and natural selection in Europe

Climate change may force organisms to adapt genetically or plastically to new environmental conditions. Invasive species show remarkable potential for rapid adaptation. The ovoviviparous New Zealand mud snail (NZMS), Potamopyrgus antipodarum, has successfully established across Europe with two clonally reproducing mitochondrial lineages since its arrival in the first half of the 19th century. Its remarkable variation in shell morphology was shown to be fitness relevant. We investigated the effects of temperature on shell morphology across 11 populations from Germany and the Iberian Peninsula in a common garden across three temperatures. We analyzed size and shape using geometric morphometrics. For both, we compared reaction norms and estimated heritabilities. For size, the interaction of temperature and haplotype explained about 50% of the total variance. We also observed more genotype by environment interactions indicating a higher degree of population differentiation than in shape. Across the three temperatures, size followed the expectations of the temperature‐size rule, with individuals growing larger in cold environments. Changes in shape may have compensated for changes in size affecting space for brooding embryos. Heritability estimates were relatively high. As indicated by the very low coefficients of variation for clonal repeatability (CV_A), they can probably not be compared in absolute terms. However, they showed some sensitivity to temperature, in haplotype t more so than in z, which was only found in Portugal. The low CV_A values indicate that genetic variation among European populations is still restricted with a low potential to react to selection. A considerable fraction of the genetic variation was due to differences between the clonal lineages. The NZMS has apparently not been long enough in Europe to accumulate significant genetic variation relevant for morphological adaptation. As temperature is obviously not the sole factor influencing shell morphology, their interaction will probably not be a factor limiting population persistence under a warming climate in Europe.

Advances in understanding the drivers of population spatial synchrony

The causes of spatial synchrony in population dynamics are often elusive. We review how recent advances have enhanced understanding of the causes of the spatial synchrony of insect populations and revealed previously underappreciated complexities in patterns of synchrony. We highlight how regional-scale studies of population genetic structure have helped elucidate the role of dispersal in population synchronization and how novel data-analytic approaches have revealed variation in spatial synchrony across timescales and geographies and the underlying drivers. We also stress the limited current understanding of the impacts of climate change on the spatial synchrony of insect populations and the potential ramifications of these effects for pest management as well as species conservation.

Temperature-sensitive development shapes insect phenological responses to climate change

Phenological shifts vary within and among insect species and locations based on exposure and sensitivity to climate change. Shifts in environmental conditions and seasonal constraints along elevation and latitudinal gradients can select for differences in temperature sensitivity that generate differential phenological shifts. I examine the phenological implications of observed variation in developmental traits. Coupling physiological and ecological insight to link the environmental sensitivity of development to phenology and fitness offers promise in understanding variable phenological responses to climate change and their community and ecosystem implications. A key challenge in establishing these linkages is extrapolating controlled, laboratory experiments to temporally variable, natural environments. New lab and field experiments that incorporate realistic environmental variation are needed to test the extrapolations. Establishing the linkages can aid understanding and anticipating impacts of climate change on insects.

Growth and development of an invasive forest insect under current and future projected temperature regimes

Temperature and its impact on fitness are fundamental for understanding range shifts and population dynamics under climate change. Geographic climate heterogeneity, behavioral and physiological plasticity, and thermal adaptation to local climates make predicting the responses of species to climate change complex. Using larvae from seven geographically distinct wild populations in the eastern United States of the non‐native forest pest Lymantria dispar dispar (L.), we conducted a simulated reciprocal transplant experiment in environmental chambers using six custom temperature regimes representing contemporary conditions near the southern and northern extremes of the US invasion front and projections under two climate change scenarios for the year 2050. Larval growth and development rates increased with climate warming compared with current thermal regimes and tended to be greater for individuals originally sourced from southern rather than northern populations. Although increases in growth and development rates with warming varied somewhat by region of the source population, there was not strong evidence of local adaptation, southern populations tended to outperform those from northern populations in all thermal regimes. Our study demonstrates the utility of simulating thermal regimes under climate change in environmental chambers and emphasizes how the impacts from future increases in temperature can vary based on geographic differences in climate‐related performance among populations.

Irreversible impact of early thermal conditions: an integrative study of developmental plasticity linked to mobility in a butterfly species

Within populations, phenotypic plasticity may allow adaptive phenotypic variation in response to selection generated by environmental heterogeneity. For instance, in multivoltine species, seasonal changes between and within generations may trigger morphological and physiological variation enhancing fitness under different environmental conditions. These seasonal changes may irreversibly affect adult phenotypes when experienced during development. Yet, the irreversible effects of developmental plasticity on adult morphology have rarely been linked to life-history traits even though they may affect different fitness components such as reproduction, mobility and self-maintenance. To address this issue, we raised larvae of Pieris napi butterflies under warm or cool conditions to subsequently compare adult performance in terms of reproduction performance (as assessed through fecundity), displacement capacity (as assessed through flight propensity and endurance) and self-maintenance (as assessed through the measurement of oxidative markers). As expected in ectotherms, individuals developed faster under warm conditions and were smaller than individuals developing under cool conditions. They also had more slender wings and showed a higher wing surface ratio. These morphological differences were associated with changes in the reproductive and flight performances of adults, as individuals developing under warm conditions laid fewer eggs and flew larger distances. Accordingly, the examination of their oxidative status suggested that individuals developing under warm conditions invested more strongly into self-maintenance than individuals developing under cool conditions (possibly at the expense of reproduction). Overall, our results indicate that developmental conditions have long-term consequences on several adult traits in butterflies. This plasticity likely acts on life history strategies for each generation to keep pace with seasonal variations and may facilitate acclimation processes in the context of climate change.

Indications for rapid evolution of trait means and thermal plasticity in range-expanding populations of a butterfly

Currently, poleward range expansions are observed in many taxa, often in response to anthropogenic climate change. At the expanding front, populations likely face cooler and more variable temperature conditions, imposing thermal selection. This may result in changes in trait means or plasticity, the relative contribution of which is not well understood. We, here, investigate evolutionary change in range-expanding populations of the butterfly Pieris mannii, by comparing populations from the core and the newly established northern range under laboratory conditions. We observed both changes in trait means and in thermal reaction norms. Range-expanding populations showed a more rapid development, potentially indicative of counter-gradient variation and an increased cold tolerance compared with core populations. Genotype-environment interactions prevailed in all associated traits, such that the above differences were restricted to cooler environmental conditions. In range-expanding populations, plasticity was decreased in developmental traits enabling relatively rapid growth even under cooler conditions but increased in cold tolerance arguably promoting higher activity under thermally challenging conditions. Notably, these changes must have occurred within a time period of ca. 10 years only. Our results suggest, in line with contemporary theory, that the evolution of plasticity may play a hitherto underestimated role for adaptation to climatic variation. However, rather than generally increased or decreased levels of plasticity, our results indicate fine-tuned, trait-specific evolutionary responses to increase fitness in novel environments.