Predicted range expansion of Prostephanus truncatus (Coleoptera: Bostrichidae) under projected climate change scenarios.

The larger grain borer (Prostephanus truncatus [Horn] [Coleoptera: Bostrichidae]) is a wood-boring insect native to Central America and adapted to stored maize and cassava. It was accidentally introduced to Tanzania and became a pest across central Africa. Unlike many grain pests, P. truncatus populations can establish and move within forests. Consequently, novel infestations can occur without human influence. The objectives of our study were to (i) develop an updated current suitability projection for P. truncatus, (ii) assess its potential future distribution under different climate change scenarios, and (iii) identify climate variables that best inform the model. We used WALLACE and MaxEnt to predict potential global distribution by incorporating bioclimatic variables and occurrence records. Future models were projected for 2050 and 2070 with Representative Concentration Pathways (RCPs) 2.6 (low change) and 8.5 (high change). Distribution was most limited by high precipitation and cold temperatures. Globally, highly suitable areas (> 75%) primarily occurred along coastal and equatorial regions with novel areas in northern South America, India, southeastern Asia, Indonesia, and the Philippines, totaling 7% under current conditions. Highly suitable areas at RCPs 2.6 and 8.5 are estimated to increase to 12% and 15%, respectively, by 2050 and increase to 19% in 2070 under RCP 8.5. Centroids of highly suitable areas show distribution centers moving more inshore and away from the equator. Notably, the result is a range expansion, not a shift. Results can be used to decrease biosecurity risks through more spatially explicit and timely surveillance programs for targeting the exclusion of this pest.

Flight capacity and behavior of Ephestia kuehniella (Lepidoptera: Pyralidae) in response to kairomonal and pheromonal stimuli.

Flight behavior is an important component to understand in the context of pest management. However, because of their small size, little is known about the flight capacity of most stored-product insects, and when a flight has been assessed, it usually consists of a propensity for initiating flight. Despite a priori expectations of the importance of flight for moths, there are no data about the flight capacity and little on the flight behavior of the Mediterranean flour moth, Ephestia kuehniella Zeller (Lepidoptera: Pyralidae). As a result, the objective of the current study was to (i) characterize the baseline flight capacity of E. kuehniella and (ii) determine how flight capacity is affected by the presence of kairomonal, pheromonal, or no stimuli. We found adult E. kuehniella flew a mean of 24-34 km in a 24-h period, and the distance flown per bout increased from 91 to 207 m in the presence of pheromones but decreased to 41 m when food was nearby compared to a negative control. The total number of flight bouts was 1.6-fold higher in the presence of pheromone compared to the negative control, but E. kuehniella flew significantly slower with pheromone and food cues present, suggesting they may be exhibiting an optimal foraging strategy. Our data on flight capacity results in qualitatively and quantitatively different conclusions about flight than those conclusions formed if only flight initiation is considered. Overall, this novel information is useful for understanding the spread within facilities and in the landscape (between facilities), as well as parameterizing ecological modeling.

The behavioral response to the putative necromones from dead Tribolium castaneum (Coleoptera: Tenebrionidae) in traps by conspecifics as a function of density and time since capture.

Long-term trapping programs of stored product pests provide information for timely and accurate pest management. Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) is a highly successful external-infesting grain pest and is frequently monitored using a commercial pitfall trap that combines pheromonal and kairomonal stimuli. However, an often overlooked component of lure-based traps is the potential for the volatile plume to change over time as individuals are captured. These now-dead insects may then release necromones altering the captures of conspecifics. In this study, we evaluated changes in (i) the behavior of T. castaneum and (ii) the relative change in volatiles over time since dead insects were added and among different densities of dead conspecifics in a commercially available kairomone oil. We used multiple behavior assays, including wind tunnel, release-recapture, and 2-way olfactometer, and performed chemical analyses via headspace collection and gas chromatography coupled with mass spectrometry. Tribolium castaneum response to the kairomone lure was not consistent among assays of density of conspecifics between 4 and 40 adults after 24 or 96 h, or time of seeding over 1-96 h or 8-11 days prior. Tested strains collected in 2012 and 2019 ruled out strain-specific differences. Oil batch effects were also ruled out as a factor contributing to the response of T. castaneum. The relative volatile composition was generally stable among the treatments despite using different seeding densities and seeding times. Given that attraction and relative volatile composition were generally unaffected by prior captures, long-term monitoring programs may be robust in their interpretability over time.

Distance-based Decision-making in Oviposition by Tribolium castaneum Herbst (Coleoptera: Tenebrionidae) on Low- and No-gluten Flours.

The increasing popularity of low- and no-gluten flours as wheat flour alternatives has driven the need to understand risks of insect pest infestation in these products. Previous research using no-choice bioassays found that the red flour beetle, Tribolium castaneum Herbst can oviposit and develop on a range of alternative flours; here we test T. castaneum preference by assessing attraction in a wind tunnel assay and oviposition preference in both small- and large-scale choice assays between alternative and wheat flour. Some flours such as buckwheat, teff, millet, rice, and rye elicit similar responses as wheat flour for both attraction and oviposition. Other flours such as cassava and oat were not preferred for either oviposition or attraction behaviors. Flours like sorghum and amaranth, had mixed preferences for oviposition, with decreased oviposition in the small arena but not the large arena. Comparisons to published developmental success rates of T. castnaeum on these dietsindicate that females can choose diets on which they have high developmental success, such as buckwheat or teff, and avoid flours like cassava where developmental success is low. However, mismatch of oviposition preference and developmental success also occurs, in flours such as rice and amaranth. These results suggest the red flour beetle has limited ability to make adaptive food selections for egg laying. Further analysis of the chemical and physical properties associated with preferred and nonpreferred flours can provide information on cues associated with egg laying as well as how these cues could be exploited in pest management programs.

Behavioral Response of Unmated Female Plodia interpunctella Hübner (Lepidoptera: Pyralidae) to Synthetic Sex Pheromone Lure.

Indian meal moth, Plodia interpunctella Hübner, is an important pest of stored products in food facilities like processing plants, warehouses, and retail stores. Mating disruption, which uses synthetic pheromone to delay or prevent mating, is a relatively new management tactic for this pest but is becoming widely adopted. However, little is known about the mechanisms behind its efficacy, including how artificial pheromone impacts female behavior. Here we assay behavioral responses of two strains of unmated female P. interpunctella exposed to pheromone. Results show one strain increased the duration of calling behavior while the other decreased calling when exposed to pheromone lures. Time walking decreased, and time cleaning increased for both strains when exposed to pheromone. Time of first walking behavior was also delayed for one strain when exposed to pheromone. Females of both strains were less mobile when exposed to pheromone. These results show autodetection of pheromone by females, but also indicate that strains may vary in behavioral responses. Differing patterns of calling behavior between strains could be driven by either strain-specific genetic differences or laboratory induced effects. Decreasing calling behavior and overall movement during exposure to pheromone could enhance the effectiveness of a mating disruption program. However, increased calling by females in the presence of pheromone may be a competitive response and could increase mating success under certain scenarios. These findings suggest that artificial pheromone associated with monitoring and mating disruption programs has impacts on female behavior and warrants further study to determine the overall impacts on program effectiveness.

Long-Lasting Insecticide-Treated Netting Affects Reproductive Output and Mating Behavior in Tribolium castaneum (Coleoptera: Tenebrionidae) and Trogoderma variabile (Coleoptera: Dermestidae).

Preventing insect infestations is a critical component for establishing a pest management plan for stored-product insects. Long-lasting insecticide-treated netting (LLIN) is a potential tool to reduce insect movement by providing a chemical barrier, where insects may be able to physically pass through but ultimately die after exposure to the netting. Sublethal effects, such as reduced movement immediately after exposure and reduced ability to colonize, have been reported. Here we examine the sublethal effects of exposure to LLIN on two beetle species, Trogoderma variabile Ballion, warehouse beetle, and Tribolium castaneum Herbst, red flour beetle. We found that both female and male T. castaneum exposed to LLIN produced significantly less adult progeny than those exposed to untreated netting. Adult progeny output did not differ for T. variabile, but survivorship increased in T. variabile females exposed to LLIN. Importantly, the overall net reproductive rate was significantly decreased for both T. variabile and T. castaneum. The number of copulation attempts did not differ between males or females exposed to LLIN compared to untreated netting, but males exposed to LLIN showed increased durations of attempted and successful copulation events. This research demonstrates that the implications of LLIN exposure extend past direct mortality, with sublethal effects on reproductive output potentially increasing the effectiveness of this tool for preventing insect infestations.

Effectiveness of long-lasting insecticide netting on Tribolium castaneum is modulated by multiple exposures, biotic, and abiotic factors.

BACKGROUND: Prevention is the first line of defense in mitigating losses of post-harvest crops. Long-lasting insecticide treated (LLIN) could be used in food facilities to expose insects to insecticide at different areas within a facility. Prior research has shown that single short exposures reduce movement and longer exposures increase mortality for stored-product insect pests, but we do not know how multiple short duration exposures and biotic and abiotic conditions affect insects exposed to LLIN. Here, we repeatedly exposed red flour beetles, Tribolium castaneum, to LLIN to assess the cumulative effects. We also examined the effects of beetle age and time of day during exposure, and temperature, humidity and food availability during recovery after a single exposure to LLIN. RESULTS: We found that four repeated 10-min exposures had similar knockdown effects as a single 30-min exposure. We also found that beetles were more affected when aged 1-6 days versus 14-20 days or were exposed at mid- or late in the day versus earlier in the day. Higher recovery levels were observed with food and at higher relative humidity. In addition, older beetles were more active than younger beetles during exposure, which could reduce time in contact with netting and partially explain why older beetles tended to be less affected. CONCLUSION: Some individuals can recover after exposure to LLIN, dependent on exposure duration and environmental factors, but our study shows that sublethal effects likely persist and future work should consider the physiology of T. castaneum before, during, and after exposure to LLIN. Published 2020. This article is a U.S. Government work and is in the public domain in the USA.

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.

Using Long-term Capture Data to Predict Trogoderma variabile Ballion and Plodia interpunctella (Hübner) Population Patterns.

Insects can infest facilities that house and process post-harvest grains and grain-based products. Integrated pest management tactics rely on tracking insect populations and using this information to select and target management tactics. Our ability to predict when and where to best focus treatment relies on an understanding of long-term trends, but often any available monitoring data are limited in its duration. Here we present data collected over a 10-year period at a flour mill in the central part of the United States. Using traps placed both inside and outside a flour mill and baited with pheromone-lures for Plodia interpunctella (Hübner), Indianmeal moth, and Trogoderma variabile Ballion, warehouse beetle, we examine environmental and spatial variability in insect captures. We find that both species, inside and outside the mill, are highly influenced by seasonal patterns, with peaks of insect captures during the warm season (April through September). There is also consistency across time and space in trap capture for P. interpunctella with traps in an open location consistently capturing high numbers of insects. In contrast, T. variabile lacked consistency in trap capture but were most often not found in the same trap locations as P. interpunctella. Fumigations conducted within the facility appeared to have little impact on insect captures inside, with dynamics appearing to be driven more by broader seasonal patterns in activity. These data and analyses suggest that there is a larger population of these insects that are readily moving in and out of the structures, while fumigation treatments are only impacting a small portion of the overall population and tactics targeting immigration may be an important addition to the pest management program.

Effect of Delayed Mating on Longevity and Reproductive Performance of Lasioderma serricorne (Coleoptera: Anobiidae).

In recent times, research has focused on integrated pest management approaches using nonchemical alternatives such as mating disruption for the control of stored product insect pests. In this study, we examined the effect of imposed delayed mating on the longevity and reproductive performance of the cigarette beetle, Lasioderma serricorne (F.), a serious insect pest of value added grain-based products, tobacco products, and spices. Delayed mating, progressing 0-14 d, was imposed on both sexes simultaneously, on males only, and on females only. Insects were observed daily for longevity, and F1 progeny was recorded 7-10 wk after mating pairs were placed together. Unmated adults lived significantly longer than mated adults, and mated females lived significantly longer than mated males. However, the length of the period of mating delay did not significantly affect the longevity of mated adults. Progeny production decreased with the age of adults at mating. The number of progeny produced when mating delay was imposed on both sexes simultaneously or on females only was significantly lower than when mating delay was imposed on males only. Hence, females were more adversely affected by delayed mating than males. Findings from this study may provide information for the development of mating disruption techniques that can delay mating and may be effective in keeping populations of L. serricorne below levels that would warrant a control action.

Speed of exposure to rapid cold hardening and genotype drive the level of acclimation response in Drosophila melanogaster.

Comparing methodologies that attempt to mimic natural conditions is important when evaluating thermal tolerances of ectotherms, as exposing animals to different artificial thermal regimes may provide conflicting information of an insect's thermal profile. Rapid cold hardening (RCH) occurs in ectotherms and typically increases survivorship to extreme cold exposure through a short, pre-treatment to a non-lethal cold temperature. Here we assess survivorship in a set of genotypes from the Drosophila melanogaster Reference Panel for direct and ramping RCH pre-treatments at cooling rates occurring under more natural conditions (0.1 °C/min and 0.5 °C/min) in combination with a direct and ramped rewarming treatment post cold exposure. We find that all three pre-treatment exposures alone significantly increase survivorship. We find significant correlations in survivorship among treatments across genotypes, suggesting that regardless of the pre-treatment, individuals of a given genotype have an innate level of acclimation. When rewarming is introduced, survivorship significantly decreased relative to pre-treatment alone and correlations of survival between phenotypes were not significant. Our results suggest that rewarming and slow RCH are costly to survival while a quicker RCH may impart physiological benefits more consistently across genotypes.

Red Flour Beetle (Coleoptera: Tenebrionidae) Response to Volatile Cues Varies With Strain and Behavioral Assay.

The red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae), is a major pest of facilities where grain is processed because of its ability to find and colonize food resource patches. Traps baited with pheromone and kairomone lures are commonly used to monitor for the presence of insects in warehouses or flour mills, for example. However, two nonmutually exclusive components, environment and genetics, could influence insect responsiveness to volatiles, impacting the efficacy of monitoring. Intraspecific variation in attraction behavior to food and mates is largely unexplored in stored-product insects, but tapping into natural genetic variation could provide a baseline for identifying genetic mechanisms associated with finding resources. Here, we assess eight strains of T. castaneum for variation in response to kairomone- and pheromone-based lures using three behavioral assays: paired choice with no forced air flow, upwind attraction with forced air flow, and movement pattern in an arena with a single odor source. We find strain-specific responses to kairomones and pheromones and evidence for heritability in behavioral responses. However, environmental coefficients for behavioral responses to both lures are high, suggesting that environment, and its potential interaction with genotype, strongly influences behavioral outcomes in these assays. Furthermore, despite the different environmental conditions among the different behavioral assays, we find a correlation for volatile preference among the assays. Our results provide a baseline assessment of natural variation for preference to kairomone and pheromone lures and suggest that careful consideration of behavioral assay is key to understanding the mechanisms of attraction in these stored-product pests.

Mobility of Adult Tribolium castaneum (Coleoptera: Tenebrionidae) and Rhyzopertha dominica (Coleoptera: Bostrichidae) After Exposure to Long-Lasting Insecticide-Incorporated Netting.

Stored products represent an enormous economic output, but insects regularly immigrate into stored products from the surrounding landscape throughout the postharvest supply chain. Long-lasting insecticide-incorporatednetting (LLIN), which usually contains an incorporated pyrethroid, has been used as part of a strategy to reduce the spread of malaria in tropical regions since the 1990s and has only recently been considered for its application in pre- and postharvest agricultural contexts. The goal of this study was to determine how short-term exposure to LLINs in the laboratory impacts the locomotory behavior and mortality for adult Tribolium castaneum (Herbst), (Coleoptera: Tenebrionidae) red flour beetle, and Rhyzopertha dominica (Fauvel), (Coleoptera: Bostrichidae) lesser grain borer, at different periods of time after exposure. Exposure to LLINs resulted in multiple-fold reductions in the distance moved and elevated angular velocity in both species that quickly took effect and persisted even after 168 h compared with adults exposed to control netting. R. dominica was somewhat more susceptible than T. castaneum to LLINs. Finally, the dispersal capacity of both species, measured as ability to move to a remote resource patch, was significantly impaired or absent after exposure to LLINs compared to adults exposed to control netting. Our results demonstrate that LLINs are a promising new technology for reducing infestation by stored product insects since even short exposures limit movement and ultimately lead to knockdown and death.

Life history changes in Trogoderma variabile and T. inclusum due to mating delay with implications for mating disruption as a management tactic.

Controlling postharvest pest species is a costly process with insecticide resistance and species-specific control requiring multiple tactics. Mating disruption (MD) can be used to both decrease a female's access to males and delay timing of mating and decreases overall mating success in a population and population growth rate. Development of new commercially available MD products requires an understanding of life history parameters associated with mating delay. These can provide information for targeting proportions of reproducing individuals using MD. After delaying mating for females of two closely related beetle species, Trogoderma variabile and T. inclusum, we surveyed survivorship, number of eggs laid, and number of progeny emerged. With increases in mating age, total number of eggs laid and total number of progeny emerged significantly declined over time. T. inclusum typically had greater numbers of eggs laid and progeny emerged compared to T. variabile as female age at mating increased, suggesting that T. inclusum may be more resistant to long-term delays in mating. Life span showed an increase as mating age increased but life span significantly decreased almost immediately following mating. Simulations depicting multiple distributions of mating within a population suggest that in a closed population, high levels of mating delay significantly reduced reproductive growth rates. Although reproductive growth rates were decreased with increased mating age, they are still large enough to maintain populations. This study highlights the differences in life history between two closely related species, suggesting that T. inclusum outperforms T. variabile over the course of a life span, but T. variabile has better reproductive capabilities early in life. MD may also be a viable component of a pest management system for these two species as it significantly decreased overall reproductive output and population growth.

Direct Testing for Allele-Specific Expression Differences Between Conditions.

Allelic imbalance (AI) indicates the presence of functional variation in cis regulatory regions. Detecting cis regulatory differences using AI is widespread, yet there is no formal statistical methodology that tests whether AI differs between conditions. Here, we present a novel model and formally test differences in AI across conditions using Bayesian credible intervals. The approach tests AI by environment (G×E) interactions, and can be used to test AI between environments, genotypes, sex, and any other condition. We incorporate bias into the modeling process. Bias is allowed to vary between conditions, making the formulation of the model general. As gene expression affects power for detection of AI, and, as expression may vary between conditions, the model explicitly takes coverage into account. The proposed model has low type I and II error under several scenarios, and is robust to large differences in coverage between conditions. We reanalyze RNA-seq data from a Drosophila melanogaster population panel, with F1 genotypes, to compare levels of AI between mated and virgin female flies, and we show that AI × genotype interactions can also be tested. To demonstrate the use of the model to test genetic differences and interactions, a formal test between two F1s was performed, showing the expected 20% difference in AI. The proposed model allows a formal test of G×E and G×G, and reaffirms a previous finding that cis regulation is robust between environments.

RNA-Seq Validation of RNAi Identifies Additional Gene Connectivity in Tribolium castaneum (Coleoptera: Tenebrionidae).

RNA interference (RNAi) is a functional genomics tool to correlate genotype and phenotype by delivering targeted, gene-specific, and complementary dsRNA into a host via injection, feeding, or other means in order to reduce gene expression. In the red flour beetle, Tribolium castaneum, RNAi has been successful via injected dsRNA at all life stages. Traditionally, successful transcript knockdown has been quantified by qPCR on a gene-by-gene basis, where only expression of the target gene and normalization genes are evaluated. In this study, RNA-Seq was used to quantify transcript expression in larvae injected with dsRNA for aspartate 1-decarboxylase (ADC), which gives a reliable phenotype of an adult with a black cuticle instead of the wild-type red-brown. ANOVA of control, mock-injected, and ADC-dsRNA injected larvae indicated that target gene expression was significantly (P = 0.002) reduced 4-fold, and the black phenotype was achieved in all adults injected with ADC-dsRNA as larvae. In a pairwise analysis, significant (P < 0.05) differential expression of other genes in ADC-injected larvae suggested connections between gene pathways. One gene, dopamine receptor 2, was increased in expression 227-fold (P = 0.025), presumably connected to previous data that showed a reduction in expression of ADC results in increased levels of dopamine. To evaluate the hypothesis that increased dopamine levels can affect mobility, T. castaneum adults injected with ADC-dsRNA as larvae were significantly impaired in movement tests compared to controls, similar to black mutants in Drosophila melanogaster. The data demonstrate that RNA-Seq can reveal gene connectivity and provide more complete data validation and analysis compared to qPCR.

Artificial selection on chill-coma recovery time in Drosophila melanogaster: Direct and correlated responses to selection.

Artificial selection can be used to create populations with extreme phenotypic responses to environmental stressors. When artificial selection is applied to a single component of a stress response, this selection may result in correlated responses in other stress responses, a phenomenon called cross-tolerance, which is ultimately controlled by the genetic correlations among traits. We selected for extreme responses to cold tolerance by selecting for chill-coma recovery time from a single temperate population of Drosophila melanogaster. Chill-coma recovery time is a common metric of low, but non-lethal, cold temperature tolerance. Replicated divergent artificial selection was applied to a genetically variable base population for 31 generations, resulting in two cold resistant, two cold susceptible, and two unselected control lines. To quantify the relationship between selection on chill-coma recovery and other metrics of thermal performance, we also measured survivorship after acute cold exposure, survivorship after chronic cold exposure, survivorship after cold exposure following a pre-treatment period (rapid cold hardening), starvation tolerance, and heat tolerance. We find that chill-coma recovery time is heritable within this population and that there is an asymmetric response to increased and decreased chill-coma recovery time. Surprisingly, we found no cross-tolerances between selection on chill-coma recovery time and the other environmental stress response traits. These results suggest that although artificial selection has dramatically altered chill-coma recovery time, the correlated response to selection on other stress response phenotypes has been negligible. The lack of a correlated response suggests that chill-coma recovery time in these selection lines is likely genetically independent from measures of cold survivorship tested here.

Buffering of Genetic Regulatory Networks in Drosophila melanogaster.

Regulatory variation in gene expression can be described by cis- and trans-genetic components. Here we used RNA-seq data from a population panel of Drosophila melanogaster test crosses to compare allelic imbalance (AI) in female head tissue between mated and virgin flies, an environmental change known to affect transcription. Indeed, 3048 exons (1610 genes) are differentially expressed in this study. A Bayesian model for AI, with an intersection test, controls type I error. There are ∼200 genes with AI exclusively in mated or virgin flies, indicating an environmental component of expression regulation. On average 34% of genes within a cross and 54% of all genes show evidence for genetic regulation of transcription. Nearly all differentially regulated genes are affected in cis, with an average of 63% of expression variation explained by the cis-effects. Trans-effects explain 8% of the variance in AI on average and the interaction between cis and trans explains an average of 11% of the total variance in AI. In both environments cis- and trans-effects are compensatory in their overall effect, with a negative association between cis- and trans-effects in 85% of the exons examined. We hypothesize that the gene expression level perturbed by cis-regulatory mutations is compensated through trans-regulatory mechanisms, e.g., trans and cis by trans-factors buffering cis-mutations. In addition, when AI is detected in both environments, cis-mated, cis-virgin, and trans-mated-trans-virgin estimates are highly concordant with 99% of all exons positively correlated with a median correlation of 0.83 for cis and 0.95 for trans We conclude that the gene regulatory networks (GRNs) are robust and that trans-buffering explains robustness.

Assessment strategies and fighting patterns in animal contests: a role for serotonin?

Accurate assessment of the probability of success in an aggressive confrontation with a conspecific is critical to the survival and fitness of the individuals. Various game theory models have examined these assessment strategies under the assumption that contests should favor the animal with the greater resource-holding potential (RHP), body size typically being the proxy. Mutual assessment asserts that an individual can assess their own RHP relative to their opponent, allowing the inferior animal the chance to flee before incurring unnecessary costs. The model of self-determined persistence, however, assumes that an individual will fight to a set personal threshold, independent of their opponent's RHP. Both models have been repeatedly tested using size as a proxy for RHP, with neither receiving unambiguous support. Here we present both morphological and neurophysiological data from size-matched and mismatched stalk-eyed fly fights. We discovered differing fighting strategies between winners and losers. Winners readily escalated encounters to higher intensity and physical contact and engaged in less low-intensity, posturing behaviors compared with losers. Although these fighting strategies were largely independent of size, they were associated with elevated levels of 5-HT. Understanding the neurophysiological factors responsible for mediating the motivational state of opponents could help resolve the inconsistencies seen in current game theory models. Therefore, we contend that current studies using only size as a proxy for RHP may be inadequate in determining the intricacies of fighting ability and that future studies investigating assessment strategies and contest outcome should include neurophysiological data.

Constraints, independence, and evolution of thermal plasticity: probing genetic architecture of long- and short-term thermal acclimation.

Seasonal and daily thermal variation can limit species distributions because of physiological tolerances. Low temperatures are particularly challenging for ectotherms, which use both basal thermotolerance and acclimation, an adaptive plastic response, to mitigate thermal stress. Both basal thermotolerance and acclimation are thought to be important for local adaptation and persistence in the face of climate change. However, the evolutionary independence of basal and plastic tolerances remains unclear. Acclimation can occur over longer (seasonal) or shorter (hours to days) time scales, and the degree of mechanistic overlap is unresolved. Using a midlatitude population of Drosophila melanogaster, we show substantial heritable variation in both short- and long-term acclimation. Rapid cold hardening (short-term plasticity) and developmental acclimation (long-term plasticity) are positively correlated, suggesting shared mechanisms. However, there are independent components of these traits, because developmentally acclimated flies respond positively to short-term acclimation. A strong negative correlation between basal cold tolerance and developmental acclimation suggests that basal cold tolerance may constrain developmental acclimation, whereas a weaker negative correlation between basal cold tolerance and short-term acclimation suggests less constraint. Using genome-wide association mapping, we show the genetic architecture of rapid cold hardening and developmental acclimation responses are nonoverlapping at the SNP and corresponding gene level. However, genes associated with each trait share functional similarities, including genes involved in apoptosis and autophagy, cytoskeletal and membrane structural components, and ion binding and transport. These results indicate substantial opportunity for short-term and long-term acclimation responses to evolve separately from each other and for short-term acclimation to evolve separately from basal thermotolerance.