The freeze-avoiding mountain pine beetle (Dendroctonus ponderosae) survives prolonged exposure to stressful cold by mitigating ionoregulatory collapse.

Insect performance is linked to environmental temperature, and surviving through winter represents a key challenge for temperate, alpine and polar species. To overwinter, insects have adapted a range of strategies to become truly cold hardy. However, although the mechanisms underlying the ability to avoid or tolerate freezing have been well studied, little attention has been given to the challenge of maintaining ion homeostasis at frigid temperatures in these species, despite this limiting cold tolerance for insects susceptible to mild chilling. Here, we investigated how prolonged exposure to temperatures just above the supercooling point affects ion balance in freeze-avoidant mountain pine beetle (Dendroctonus ponderosae) larvae in autumn, mid-winter and spring, and related it to organismal recovery times and survival. Hemolymph ion balance was gradually disrupted during the first day of exposure, characterized by hyperkalemia and hyponatremia, after which a plateau was reached and maintained for the rest of the 7-day experiment. The degree of ionoregulatory collapse correlated strongly with recovery times, which followed a similar asymptotical progression. Mortality increased slightly during extensive cold exposures, where hemolymph K+ concentration was highest, and a sigmoidal relationship was found between survival and hyperkalemia. Thus, the cold tolerance of the freeze-avoiding larvae of D. ponderosae appears limited by the ability to prevent ionoregulatory collapse in a manner similar to that of chill-susceptible insects, albeit at much lower temperatures. Based on these results, we propose that a prerequisite for the evolution of insect freeze avoidance may be a convergent or ancestral ability to maintain ion homeostasis during extreme cold stress.

Geographic variation in larval cold tolerance and exposure across the invasion front of a widely established forest insect.

Under global climate change, high and low temperature extremes can drive shifts in species distributions. Across the range of a species, thermal tolerance is based on acclimatization, plasticity, and may undergo selection, shaping resilience to temperature stress. In this study, we measured variation in cold temperature tolerance of early instar larvae of an invasive forest insect, Lymantria dispar dispar L. (Lepidoptera: Erebidae), using populations sourced from a range of climates within the current introduced range in the Eastern United States. We tested for population differences in chill coma recovery (CCR) by measuring recovery time following a period of exposure to a nonlethal cold temperature in 2 cold exposure experiments. A 3rd experiment quantified growth responses after CCR to evaluate sublethal effects. Our results indicate that cold tolerance is linked to regional climate, with individuals from populations sourced from colder climates recovering faster from chill coma. While this geographic gradient is seen in many species, detecting this pattern is notable for an introduced species founded from a single point-source introduction. We demonstrate that the cold temperatures used in our experiments occur in nature during cold spells after spring egg hatch, but impacts to growth and survival appear low. We expect that population differences in cold temperature performance manifest more from differences in temperature-dependent growth than acute exposure. Evaluating intraspecific variation in cold tolerance increases our understanding of the role of climatic gradients on the physiology of an invasive species, and contributes to tools for predicting further expansion.

Effect of brief exposures of anesthesia on thermotolerance and metabolic rate of the spotted-wing fly, Drosophila suzukii: Differences between sexes?

The spotted-wing fly, Drosophila suzukii, is a world-wide pest insect for which there is increasing interest in its physiological traits including metabolism and thermotolerance. Most studies focus only on survival to different time exposures to extreme temperatures, mainly in female flies. In addition, it has not been tested yet how anesthesia affects these measurements. We analyzed the effects of anesthesia by brief exposures to cold, anoxia by CO2 or N2 on three standard thermotolerance assays, as well as the aerobic metabolic rate in both sexes. For heat tolerance we measured CTmax by thermolimit respirometry, and CTmin and chill-coma recovery time for cold tolerance. Aerobic metabolism was calculated by CO2 production of individual flies in real time by open flow respirometry. Results showed that females have a significantly higher V̇CO2 for inactive (at 25 °C) and maximum metabolic rate than males. This difference is mainly explained by body mass and disappears after mass correction. Males had a more sensitive MR to temperature than females showed by a significantly higher Q10 (2.19 vs. 1.98, for males and females, respectively). We observed a significantly lower CTmin (X2 = 4.27, P = 0.03) in females (3.68 ± 0.38 °C) than males (4.56 ± 0.39 °C), although we did not find significant effects of anesthesia. In contrast, anesthesia significantly modifies CTmax for both sexes (F3,62 = 7.86, P < 0.001) with a decrease of the CTmax in cold-anesthetized flies. Finally, we found a significantly higher CTmax in females (37.87 ± 0.07 °C) than males (37.36 ± 0.09 °C). We conclude that cold anesthesia seems to have detrimental effects on heat tolerance, and females have broader thermotolerance range than males, which could help them to establish in invaded temperate regions with more variable environmental temperatures.

ShK-Domain-Containing Protein from a Parasitic Nematode Modulates Drosophila melanogaster Immunity.

A key component to understanding host-parasite interactions is the molecular crosstalk between host and parasite. Excreted/secreted products (ESPs) released by parasitic nematodes play an important role in parasitism. They can directly damage host tissue and modulate host defense. Steinernema carpocapsae, a well-studied parasite of insects releases approximately 500 venom proteins as part of the infection process. Though the identity of these proteins is known, few have been studied in detail. One protein family present in the ESPs released by these nematodes is the ShK family. We studied the most abundant ShK-domain-containing protein in S. carpocapsae ESPs, Sc-ShK-1, to investigate its effects in a fruit fly model. We found that Sc-ShK-1 is toxic under high stress conditions and negatively affects the health of fruit flies. We have shown that Sc-ShK-1 contributes to host immunomodulation in bacterial co-infections resulting in increased mortality and microbial growth. This study provides an insight on ShK-domain-containing proteins from nematodes and suggests these proteins may play an important role in host-parasite interactions.

Stress Resistance Traits under Different Thermal Conditions in Drosophila subobscura from Two Altitudes.

Global warming and climate change are affecting many insect species in numerous ways. These species can develop diverse mechanisms as a response to variable environmental conditions. The rise in mean and extreme temperatures due to global warming and the importance of the population's ability to adapt to temperature stress will further increase. In this study, we investigated thermal stress response, which is considered to be one of the crucial elements of population fitness and survival in fast-changing environments. The dynamics and variation of thermal stress resistance traits in D. subobscura flies originating from two natural populations sampled from different altitudes were analysed. Three different temperature regimes (25 °C, 19 °C, and 16 °C) were used for the F1 progeny from both localities to establish six experimental groups and investigate stress resistance traits: desiccation resistance, heat knock-down resistance, starvation resistance, and chill-coma recovery time. We detected that laboratory thermal conditions and population origin may have an effect on the analysed traits, and that sex also significantly influences stress resistance. Individuals from the lower altitude reared at higher temperatures show inferior resistance to thermal shock.

Cold adaptation drives population genomic divergence in the ecological specialist, Drosophila montana.

Detecting signatures of ecological adaptation in comparative genomics is challenging, but analysing population samples with characterised geographic distributions, such as clinal variation, can help identify genes showing covariation with important ecological variation. Here, we analysed patterns of geographic variation in the cold-adapted species Drosophila montana across phenotypes, genotypes and environmental conditions and tested for signatures of cold adaptation in population genomic divergence. We first derived the climatic variables associated with the geographic distribution of 24 populations across two continents to trace the scale of environmental variation experienced by the species, and measured variation in the cold tolerance of the flies of six populations from different geographic contexts. We then performed pooled whole genome sequencing of these six populations, and used Bayesian methods to identify SNPs where genetic differentiation is associated with both climatic variables and the population phenotypic measurements, while controlling for effects of demography and population structure. The top candidate SNPs were enriched on the X and fourth chromosomes, and they also lay near genes implicated in other studies of cold tolerance and population divergence in this species and its close relatives. We conclude that ecological adaptation has contributed to the divergence of D. montana populations throughout the genome and in particular on the X and fourth chromosomes, which also showed highest interpopulation FST . This study demonstrates that ecological selection can drive genomic divergence at different scales, from candidate genes to chromosome-wide effects.

Plastic changes in cold and drought tolerance of Drosophila nepalensis correlate with sex-specific differences in body melanization, cuticular lipid mass, proline accumulation, and seasonal abundance.

Autumn-collected flies of Himalayan Drosophila nepalensis differ in body color phenotypes (males more melanized relative to females) and in their behavior (males abundant in the open sites vs. shelters-seeking females). In contrast, winter-collected flies of both sexes are equally melanized and abundant in the open sites. We tested developmental and adult plasticity changes in cold or drought tolerance in D. nepalensis flies reared under winter or autumn simulated conditions. In D. nepalensis flies reared at 21 °C, male flies were more cold tolerant (as shown by shorter chill-coma recovery time and lower cold-shock mortality). Further, male flies also exhibited greater drought tolerance (increased levels of desiccation resistance, cuticular lipid mass, melanization, hydration level, and dehydration tolerance) as compared to females. We observed sex-specific differences in the adult plasticity responses due to rapid cold or drought hardening (RCH or RDH); and for the persistence of cold acclimation effects. RCH or RDH-induced changes in the level of proline accumulations are negatively correlated with a decrease in the chill-coma recovery time. Therefore, cold or drought hardening treatments are likely to influence cold tolerance through proline accumulation. Developmental acclimation and adult hardening responses revealed significant interaction effects between sexes and thermal treatments. Thus, sex-specific differences in morphological traits (body melanization and cuticular lipid mass) and physiological traits (adult plasticity changes in cold tolerance and proline accumulation) correlate with behavioral divergence (habitat usage) across sexes.

Evolution of cold tolerance and thermal plasticity in life history, behaviour and physiology during a poleward range expansion.

Many species that are moving polewards encounter novel thermal regimes to which they have to adapt. Therefore, rapid evolution of thermal tolerance and of thermal plasticity in fitness-related traits in edge populations can be crucial for the success and speed of range expansions. We tested for adaptation in cold tolerance and in life history, behavioural and physiological traits and their thermal plasticity during a poleward range expansion. We reconstructed the thermal performance curves of life history (survival, growth and development rates), behaviour (food intake) and cold tolerance (chill coma recovery time) in the aquatic larval stage of the damselfly Ischnura elegans that is currently showing a poleward range expansion in northern Europe. We studied larvae from three edge and three core populations using a common-garden experiment. Consistent with the colder annual temperatures, larvae at the expansion front evolved an improved cold tolerance. The edge populations showed no overall (across temperatures) evolution of a faster life history that would improve their range-shifting ability. Moreover, consistent with damselfly edge populations from colder latitudes, edge populations evolved at the highest rearing temperature (28°C) a faster development rate, likely to better exploit the rare periods with higher temperatures. This was associated with a higher food intake and a lower metabolic rate. In conclusion, our results suggest that the edge populations rapidly evolved adaptive changes in trait means and thermal plasticity to the novel thermal conditions at the edge front. Our results highlight the importance of considering besides trait plasticity and the evolution of trait means, also the evolution of trait plasticity to improve forecasts of responses to climate change.

Durante su expansión hacia los polos, las especies encuentran nuevos regímenes de temperatura a los que tienen que adaptarse. Por esto, una rápida evolución de la tolerancia térmica y de la plasticidad térmica de rasgos fisiológicos clave en las poblaciones del borde del área de distribución es crucial para el éxito y la velocidad de las expansiones de rango. En este estudio testamos la adaptación de la tolerancia la frío y la plasticidad térmica de rasgos de historia de vida, comportamiento y fisiológicos durante una expansión de rango hacia el norte. Reconstruimos las curvas de rendimiento térmico de rasgos de historia de vida (supervivencia, tasa de crecimiento y tasa de desarrollo) y comportamiento (ingestión de alimento), así como la tolerancia al frío (tiempo de recuperación del coma por frío) en la larva acuática de la especie de caballito del diablo Ischnura elegans, especie que muestra un rango de expansión actual en el norte de Europa. Estudiamos larvas de tres poblaciones de la región de expansión norte y tres poblaciones de la región central usando experimentos en laboratorio. En concordancia con las temperaturas más bajas, las larvas del área de expansión mostraron mayor tolerancia al frío. Sin embargo, estas larvas no mostraron en general (a lo largo de las temperaturas estudiadas) evolución hacia una historia de vida más rápida, que aumentaría su habilidad para expandirse. Además, en consistencia con la menor temperatura de la región de expansión, las larvas presentaron mayor tasa de desarrollo a la temperatura experimental más alta (28°C), probablemente para explotar mejor los infrecuentes períodos con altas temperaturas en dicha región. Esto estuvo asociado con una mayor ingestión de alimento y una menor tasa metabólica. En conclusión, nuestros resultados sugieren que los valores medios y la plasticidad de los rasgos estudiados de las poblaciones del frente de expansión evolucionaron rápidamente para adaptarse a las nuevas condiciones térmicas en dicha región. Asimismo, nuestros resultados destacan la importancia de considerar, además de la media y plasticidad de los rasgos, la evolución de esta plasticidad, con el fin de mejorar las predicciones de las respuestas de las especies al cambio climático.

Silencing the Myosin Regulatory Light Chain Gene sqh Reduces Cold Hardiness in Ophraella communa LeSage (Coleoptera: Chrysomelidae).

Ambrosia artemisiifolia is a noxious invasive alien weed, that is harmful to the environment and human health. Ophraella communa is a biocontrol agent for A. artemisiifolia, that was accidentally introduced to the Chinese mainland and has now spread throughout southern China. Recently, we found that upon artificial introduction, O. communa can survive in northern China as well. Therefore, it is necessary to study the cold hardiness of O. communa. Many genes have been identified to play a role in cold-tolerance regulation in insects, but the function of the gene encoding non-muscle myosin regulatory light chain (MRLC-sqh) remains unknown. To evaluate the role played by MRLC-sqh in the cold-tolerance response, we cloned and characterized MRLC-sqh from O. communa. Quantitative real-time PCR revealed that MRLC-sqh was expressed at high levels in the gut and pupae of O. communa. The expression of MRLC-sqh was shown to decrease after cold shock between 10 and 0 °C and ascend between 0 and -10 °C, but these did not show a positive association between MRLC-sqh expression and cold stress. Silencing of MRLC-sqh using dsMRLC-sqh increased the chill-coma recovery time of these beetles, suggesting that cold hardiness was reduced in its absence. These results suggest that the cold hardiness of O. communa may be partly regulated by MRLC-sqh. Our findings highlight the importance of motor proteins in mediating the cold response in insects.

Intraspecific variation in thermal acclimation and tolerance between populations of the winter ant, Prenolepis imparis.

Thermal phenotypic plasticity, otherwise known as acclimation, plays an essential role in how organisms respond to short-term temperature changes. Plasticity buffers the impact of harmful temperature changes; therefore, understanding variation in plasticity in natural populations is crucial for understanding how species will respond to the changing climate. However, very few studies have examined patterns of phenotypic plasticity among populations, especially among ant populations. Considering that this intraspecies variation can provide insight into adaptive variation in populations, the goal of this study was to quantify the short-term acclimation ability and thermal tolerance of several populations of the winter ant, Prenolepis imparis. We tested for correlations between thermal plasticity and thermal tolerance, elevation, and body size. We characterized the thermal environment both above and below ground for several populations distributed across different elevations within California, USA. In addition, we measured the short-term acclimation ability and thermal tolerance of those populations. To measure thermal tolerance, we used chill-coma recovery time (CCRT) and knockdown time as indicators of cold and heat tolerance, respectively. Short-term phenotypic plasticity was assessed by calculating acclimation capacity using CCRT and knockdown time after exposure to both high and low temperatures. We found that several populations displayed different chill-coma recovery times and a few displayed different heat knockdown times, and that the acclimation capacities of cold and heat tolerance differed among most populations. The high-elevation populations displayed increased tolerance to the cold (faster CCRT) and greater plasticity. For high-temperature tolerance, we found heat tolerance was not associated with altitude; instead, greater tolerance to the heat was correlated with increased plasticity at higher temperatures. These current findings provide insight into thermal adaptation and factors that contribute to phenotypic diversity by revealing physiological variance among populations.

Artificial Selection to a Nonlethal Cold Stress in Trogoderma variabile Shows Associations With Chronic Cold Stress and Body Size.

Extreme temperature has been used as an alternative to chemical treatments for stored product pests for years. Resistance to heat or cold treatments has not been documented in stored product insects, but repeated use of ineffective treatments could lead to adaptive tolerance. Trogoderma variabile (Dermestidae) is a common pest of stored products, and the larval stage is highly resistant to cold and destructive. We artificially selected populations by inducing chill coma at four different cold temperature treatments: 3 and 5 h at -10°C and 3 and 5 h at 0°C. Recovery time was highly heritable after selection for seven generations for decreased recovery time (cold tolerance) and increased recovery time (cold susceptibility) at all time and temperature combinations. Three replicate populations for each time and temperature combination varied substantially, suggesting different mutations in each population were probably responsible for selected phenotypes. Body size decreased in populations selected for cold susceptibility compared with those selected for cold tolerance and survivorship to long-term cold stress increased in the cold-tolerant populations compared with the susceptible populations. After the cessation of the selection experiment, cold tolerance dissipated within four generations from the populations at -10°C, but was maintained in populations exposed to 0°C. Our results suggest that warehouse beetles can adapt to cold stress quickly, but in the absence of cold stress, the proportion of cold-tolerant/susceptible individuals is quickly reduced, suggesting that some of the mutations responsible for these phenotypes may be associated with fitness costs under normal conditions.

Three Quantitative Trait Loci Explain More than 60% of Variation for Chill Coma Recovery Time in a Natural Population of Drosophila ananassae.

Ectothermic species such as insects are particularly vulnerable to climatic fluctuations. Nevertheless, many insects that evolved and diversified in the tropics have successfully colonized temperate regions all over the globe. To shed light on the genetic basis of cold tolerance in such species, we conducted a quantitative trait locus (QTL) mapping experiment for chill coma recovery time (CCRT) in Drosophila ananassae, a cosmopolitan species that has expanded its range from tropical to temperate regions. We created a mapping population of recombinant inbred advanced intercross lines (RIAILs) from two founder strains with diverging CCRT phenotypes. The RIAILs were phenotyped for their CCRT and, together with the founder strains, genotyped for polymorphic markers with double-digest restriction site-associated DNA (ddRAD) sequencing. Using a hierarchical mapping approach that combined standard interval mapping and a multiple-QTL model, we mapped three QTL which altogether explained 64% of the phenotypic variance. For two of the identified QTL, we found evidence of epistasis. To narrow down the list of cold tolerance candidate genes, we cross-referenced the QTL intervals with genes that we previously identified as differentially expressed in response to cold in D. ananassae, and with thermotolerance candidate genes of D. melanogaster Among the 58 differentially expressed genes that were contained within the QTL, GF15058 showed a significant interaction of the CCRT phenotype and gene expression. Further, we identified the orthologs of four D. melanogaster thermotolerance candidate genes, MtnA, klarsicht, CG5246 (D.ana/GF17132) and CG10383 (D.ana/GF14829) as candidates for cold tolerance in D. ananassae.

Thermal Tolerance Plasticity in Chagas Disease Vectors Rhodnius prolixus (Hemiptera: Reduviidae) and Triatoma infestans.

Temperature is recognized as the most influential abiotic factor on the distribution and dispersion of most insect species including Rhodnius prolixus (Stål, 1859) and Triatoma infestans (Klug, 1834), the two most important Chagas disease vectors. Although, these species thermotolerance range is well known their plasticity has never been addressed in these or any other triatomines. Herein, we investigate the effects of acclimation on thermotolerance range and resistance to stressful low temperatures by assessing thermal critical limits and 'chill-coma recovery time' (CCRT), respectively. We found positive effects of acclimation on thermotolerance range, especially on the thermal critical minimum of both species. In contrast, CCRT did not respond to acclimation in either. Our results reveal the plasticity of these Triatomines thermal tolerance in response to a wide range of acclimation temperatures. This presumably represents a physiological adaptation to daily or seasonal temperature variation with concomitant improvement in dispersion potential.

Loss of ion homeostasis is not the cause of chill coma or impaired dispersal in false codling moth Thaumatotibia leucotreta (Lepidoptera: Tortricidae).

Dispersal is a central requirement of a successful sterile insect release programme, but field-released false codling moth (FCM) typically suffer from poor dispersal ability, especially at low ambient temperatures. Here we test the hypothesis that poor activity and dispersal in FCM is caused by delayed or perturbed recovery of ion and/or water homeostasis after chilling for handling and transport prior to field release. Hemolymph and flight muscle were collected from two treatment groups at three time points that targeted thermal conditions above and below the chill coma induction threshold of ~ 6 °C: 1) control moths kept at 25 °C, 2) moths exposed to 3 °C or 9 °C for 4 h, and 3) moths allowed to recover at 25 °C for 24 h after exposure to either 3 °C or 9 °C. We measured concentrations of Na+, K+ and Mg2+ in the hemolymph and muscle collected at each time point. Exposure to a chill-coma inducing temperature had little effect overall on ion balance in the hemolymph and flight muscle of false codling moth, but hemolymph [Na+] decreased from 10.4 ±â€¯0.4 mM to 6.9 ±â€¯0.7 mM as moths were chilled to 3 °C and then increased to 10.4 ±â€¯0.9 mM after the 24 h recovery period. In the 9 °C cooling treatment, [K+] increased from 8.2 ±â€¯0.5 mM during chilling to 14.1 ±â€¯1.9 mM after the 24 h recovery period. No changes were seen in equilibrium potentials in either of the ions measured. Thus, we did not find evidence that water and ion homeostasis are lost by the moths in chill coma and conclude that reduced dispersal in field-released moths is not direct a consequence of the costs of re-establishment of homeostasis.

Functional Analysis of a Putative Target of Spatially Varying Selection in the Menin1 Gene of Drosophila melanogaster.

While significant effort has been devoted to investigating the potential influence of spatially varying selection on genomic variation, relatively little effort has been devoted to experimental analysis of putative variants or genes experiencing such selection. Previous population genetic work identified an amino acid polymorphism in the Mnn1 gene as one of the most strongly latitudinally differentiated SNPs in the genome of Drosophila melanogaster in the United States and Australia. Here we report the results of our transgenic analysis of this amino acid polymorphism. Genotypes carrying alternative Mnn1 alleles differed in multiple phenotypes in a direction generally consistent with phenotypic differences previously observed along latitudinal clines. These results support inferences from earlier population genomic work that this variant influences fitness, and support the idea that the alleles exhibiting clines may be likely to have pleiotropic effects that are correlated along the axes favored by natural selection.

Context-dependent effects of cold stress on behavioral, physiological, and life-history traits of the red flour beetle.

Animals are exposed in nature to a variety of stressors. While stress is generally harmful, mild stress can also be beneficial and contribute to reproduction and survival. We studied the effect of five cold shock events versus a single cold shock and a control group, representing three levels of stress (harsh, mild, and no stress), on behavioral, physiological, and life-history traits of the red flour beetle (Tribolium castaneum, Herbst 1797). Beetles exposed to harsh cold stress were less active than a control group: they moved less and failed more frequently to detect a food patch. Their probability to mate was also lower. Beetle pairs exposed to harsh cold stress frequently failed to reproduce at all, and if reproducing, females laid fewer eggs, which were, as larvae in mid-development, smaller than those in the control group. However, harsh cold stress led to improved female starvation tolerance, probably due to enhanced lipid accumulation. Harsh cold shock also improved tolerance to an additional cold shock compared to the control. Finally, a single cold shock event negatively affected fewer measured response variables than the harsh cold stress, but also enhanced neither starvation tolerance nor tolerance to an additional cold shock. The consequences of a harsher cold stress are thus not solely detrimental but might even enhance survival under stressful conditions. Under benign conditions, nevertheless, harsh stress impedes beetle performance. The harsh stress probably shifted the balance point of the survival-reproduction trade-off, a shift that did not take place following exposure to mild stress.

Transcriptome Analysis Reveals Candidate Genes for Cold Tolerance in Drosophila ananassae.

Coping with daily and seasonal temperature fluctuations is a key adaptive process for species to colonize temperate regions all over the globe. Over the past 18,000 years, the tropical species Drosophila ananassae expanded its home range from tropical regions in Southeast Asia to more temperate regions. Phenotypic assays of chill coma recovery time (CCRT) together with previously published population genetic data suggest that only a small number of genes underlie improved cold hardiness in the cold-adapted populations. We used high-throughput RNA sequencing to analyze differential gene expression before and after exposure to a cold shock in coldtolerant lines (those with fast chill coma recovery, CCR) and cold-sensitive lines (slow CCR) from a population originating from Bangkok, Thailand (the ancestral species range). We identified two candidate genes with a significant interaction between cold tolerance and cold shock treatment: GF14647 and GF15058. Further, our data suggest that selection for increased cold tolerance did not operate through the increased activity of heat shock proteins, but more likely through the stabilization of the actin cytoskeleton and a delayed onset of apoptosis.

Heritability and Evolutionary Potential Drive Cold Hardiness in the Overwintering Ophraella communa Beetles.

Chill tolerance plays a crucial role that allows insect species to adapt to cold environments. Two Chinese geographical populations (Laibin and Yangzhou populations) were selected to understand the chill resistance and evolutionary potential in the Ophraella communa, a biological control agent of the invasive common ragweed, Ambrosia artemisiifolia. Super-cooling point assays, knockdown tests under static low-temperature conditions and determination of glycerol content were studied. ANOVAs indicated significant differences regarding chill coma recovery time, super-cooling point, and glycerol content across populations and sexes. The narrow-sense heritability (h2) estimates of cold resistance based on a parental half-sibling breeding design ranged from 0.39 to 0.53, and the h2 value was significantly higher in the Yangzhou population than in the Laibin population. Additive genetic variances were significantly different from zero for cold tolerance. The Yangzhou population of O. communa has a strong capability to quickly gain resistance to cold. We conclude that the O. communa beetle has a plasticity that can provide cold resistance in the changing climate conditions.

Thermal acclimation is not induced by habitat-of-origin, maintenance temperature, or acute exposure to low or high temperatures in a pit-building wormlion (Vermileo sp.).

Wormlions are sit-and-wait insect predators that construct pit-traps to capture arthropod prey. They require loose soil and shelter from direct sun, both common in Mediterranean cities, and explaining their high abundance in urban habitats. We studied different aspects of thermal acclimation in wormlions. We compared chill-coma recovery time (CCRT) and heat-shock recovery time (HSRT) of wormlions from urban, semi-urban and natural habitats, expecting those originating from the urban habitat to be more heat tolerant and less cold tolerant. However, no differences were detected among the three habitats. We then examined whether maintenance temperature affects CCRT and HSRT, and expected beneficial acclimation. However, CCRT was unaffected by maintenance temperature, while temperature affected HSRT in an opposite direction to our prediction: wormlions maintained under the higher temperatures took longer to recover. When testing with two successive thermal shocks, wormlions took longer to recover from both cold and heat shock after applying an initial cold shock. We therefore conclude that cold shock inflicts some damage rather than induces acclimation. Finally, both cold- and heat-shocked wormlions constructed smaller pits than wormlions of a control group. Smaller pits probably translate to a lower likelihood of capturing prey and also limit the size of the prey, indicating a concrete cost of thermal shock. In summary, we found no evidence for thermal acclimation related either to the habitat-of-origin or to maintenance temperatures, but, rather, negative effects of unfavorable temperatures.

Environmental and genetic control of cold tolerance in the Glanville fritillary butterfly.

Thermal tolerance has a major effect on individual fitness and species distributions and can be determined by genetic variation and phenotypic plasticity. We investigate the effects of developmental and adult thermal conditions on cold tolerance, measured as chill coma recovery (CCR) time, during the early and late adult stage in the Glanville fritillary butterfly. We also investigate the genetic basis of cold tolerance by associating CCR variation with polymorphisms in candidate genes that have a known role in insect physiology. Our results demonstrate that a cooler developmental temperature leads to reduced cold tolerance in the early adult stage, whereas cooler conditions during the adult stage lead to increased cold tolerance. This suggests that adult acclimation, but not developmental plasticity, of adult cold tolerance is adaptive. This could be explained by the ecological conditions the Glanville fritillary experiences in the field, where temperature during early summer, but not spring, is predictive of thermal conditions during the butterfly's flight season. In addition, an amino acid polymorphism (Ala-Glu) in the gene flightin, which has a known function in insect flight and locomotion, was associated with CCR. These amino acids have distinct biochemical properties and may thus affect protein function and/or structure. To our knowledge, our study is the first to link genetic variation in flightin to cold tolerance, or thermal adaptation in general.