Biology subjects

Ragland, G. J.

Publications and source records attributed to Ragland, G. J..

9 recordsLinked to original sources

bioRxiv2026

Transcriptomics of cold stress and recovery reveal strongly tissue-specific responses

Cellular stress responses are often characterized as conserved, cell-autonomous processes. However, it remains unclear whether stress responses are coordinated uniformly across tissues within complex organisms, particularly during ecologically relevant conditions. We investigated tissue- and stage-specific transcriptional responses to cold stress in Drosophila melanogaster. Adults and larvae were independently exposed to a gradual cooling and recovery time series, and three adult tissues (gut, ovary, brain) and one larval tissue (gut) were sampled at baseline, at two time points that spanned the critical thermal minimum (before and during chill coma), and after recovery to rearing temperature. Transcriptomic analyses revealed strongly tissue- and stage-specific responses to cold stress, with limited overlap in differentially expressed genes or functional enrichment across tissues. These results indicate that the organismal response to thermal stress at the transcriptional level is not coordinated by a unified transcriptional program, but rather by largely distinct, tissue-specific regulatory processes.

bioinformatics↗

bioRxiv2025

A hormetic model of rapid cold hardening in Drosophila melanogaster reveals threshold effects on survival and low fertility resilience

Variable thermal environments may have both detrimental and beneficial effects. For example, extreme temperatures may challenge homeostasis and inflict tissue damage but may also induce acclimation that improves stress resilience. Hormetic models provide a framework to understand dosage-dependent, contrasting beneficial and detrimental effects from physiological and ecological perspectives. We used a hormetic framework and associated quantitative models to investigate how a range of relatively cold, pre-exposure temperatures influence survival and fertility following cold shock at a more extreme cold temperature in the fruit fly Drosophila melanogaster. Cold pre-exposure can induce a protective rapid cold hardening (RCH) response, fail to stimulate a response, or cause direct cold injury. We found a plateau-shaped relationship between pre-exposure temperature and female survival resilience, where survival following a cold shock remains high across a range of temperatures, with sharp transitions at higher and lower temperatures. Bayesian fitting of a bi-logistic model highlights these transitions at temperature thresholds that govern processes mediating both acclimation and cold injury. In contrast to survival, female fertility resilience exhibited a muted response to pre-exposure temperature in the presence and absence of post-stress mating opportunities. Overall, a range of pre-exposure temperatures allowed low but successful reproduction following cold shock. High survival but low fertility resilience is consistent with a) differential impacts of cold on somatic and reproductive tissues and b) a growing body of literature suggesting that the thermal sensitivity of fertility may be more limiting than survival for population persistence in variable and changing climates. Summary statementA hormetic model shows how sharp temperature thresholds govern beneficial rapid cold hardening and detrimental cold injury that have well-defined effects on survival, but only weakly affect fertility.

physiology↗

bioRxiv2023

VARIABILITY IN THERMAL SENSITIVITY OF ADULT REPRODUCTIVE DIAPAUSE IN THE SPRUCE BEETLE, DENDROCTONUS RUFIPENNIS

Diapause induction and termination, which regulate seasonal insect life cycles, can be highly variable within and among populations because these traits are often genetically variable and sensitive to environmental fluctuations. Both types of variation may influence how insect populations respond plastically or evolutionarily to changing climates. In this study we assessed variability in the expression of reproductive diapause in spruce beetles (Dendroctonus rufipennis), a major forest pest whose life cycle timing is regulated by both a prepupal and adult reproductive diapause. Prepupal diapause is facultative and dependent on temperature in the field, whereas previous studies suggest that adult reproductive diapause is effectively obligate. We tested for variability in adult reproductive diapause termination within and between two populations of spruce bark beetle collected from sites in Colorado and Wyoming and reared under warm, summer-like conditions in the laboratory. We also sampled beetles from under tree bark during the fall and spring to estimate how reproductive diapause might terminate naturally in the field. We present evidence that though most beetles induce and do not terminate diapause under constant warm conditions, a small proportion of females from both populations developed mature ovaries and successfully reproduced under warm conditions in the lab. Previous studies have suggested that most beetles require exposure to relatively low temperatures for several weeks to months to terminate diapause in the lab. We found that most female beetles sampled in the field had mature ovaries relatively early in the fall, suggesting that exposure to transiently low temperatures in the field may rapidly terminate adult reproductive diapause. Thus, adult reproductive arrest may primarily act as a block to prevent offspring production prior to winter and appears unnecessary for survival overwinter. Overall, our data do not suggest that major shifts in spruce beetle life cycles as mediated by adult reproductive diapause are immediately imminent with changing climates but, if the variability that we observed is heritable, adult reproductive diapause may have some capacity to evolve in both populations. ** Note ** all figures/tables designated with S are supplemental figures/tables that will appear only in the supplement in the published version. They are provided here alongside the main figures/tables, in-line in the order that they appear in the text for convenience.

ecology↗

bioRxiv2023

Variation in thermal sensitivity of diapause development among individuals and over time drives life history timing patterns in an insect pest

Physiological time is important for understanding the development and seasonal timing of ectothermic animals, but has largely been applied to developmental processes that occur during spring and summer such as morphogenesis. There is a substantial knowledge gap in the relationship between temperature and development during winter, a season that is increasingly impacted by climate change. Most temperate insects overwinter in diapause, a developmental process with little obvious morphological change. We used principles from the physiological time literature to measure and model the thermal sensitivity of diapause development rate in the apple maggot fly Rhagoletis pomonella, a univoltine fly whose diapause duration varies substantially within and among populations. We show that diapause duration can be predicted by modeling a relationship between temperature and development rate that is shifted towards lower temperatures compared to typical models of morphogenic, non-diapause development. However, incorporating interindividual variation and ontogenetic variation in the temperature-to-development-rate relationship was critical for accurately predicting fly emergence, as diapause development proceeded more quickly at high temperatures later in diapause. We conclude that the conceptual framework may be flexibly applied to other insects and discuss possible mechanisms of diapause timers and implications for phenology with warming winters.

physiology↗

bioRxiv2023

Cold tolerance and diapause within across trophic levels: endoparasitic wasps and their fly host have similar phenotypes

Low temperatures associated with winter can limit the survival of organisms, especially ectotherms whose body temperature is similar to their environment. Important adaptations for overwintering such as cold hardiness and diapause have been well-explored in many insect taxa. However, there is a gap in understanding how overwintering may vary among groups of species that interact closely, such as multiple parasitoid species that attack the same host insect. Our study investigated cold tolerance and diapause phenotypes in three endoparasitoid wasps of the apple maggot fly Rhagoletis pomonella (Diptera: Tephritidae): Utetes canaliculatus, Diachasma alloeum, and Diachasmimorpha mellea (Hymenoptera: Braconidae). Using a combination of respirometry and eclosion tracking, we detected diapause phenotypes in all three wasp species, remarkably similar to the fly host. Weak diapause was rare (< 5%) in all three wasp species, and while most D. mellea (93%) entered prolonged diapause under warm conditions, the majority of U. canaliculatus (92%) and D. alloeum (72%) averted diapause (non-diapause). There was limited interspecific variation in acute cold tolerance among the three wasp species: wasps and flies had similarly high survival (>87%) following exposure to extreme low temperatures (- 20{degrees}C) as long as their body fluids did not freeze. The wasp species showed little interspecific variation in survival following prolonged exposure to mild chilling of 8 or more weeks at 4{degrees}C. This study shows remarkable conservation of cold tolerance and diapause phenotypes within and across trophic levels. The interaction between diapause phenotype and cold hardiness in these parasitoids is an interesting direction for future research. Graphical Abstract and Highlights O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=133 SRC="FIGDIR/small/522725v1_ufig1.gif" ALT="Figure 1"> View larger version (23K): org.highwire.dtl.DTLVardef@826a3aorg.highwire.dtl.DTLVardef@c3963org.highwire.dtl.DTLVardef@8baa33org.highwire.dtl.DTLVardef@1530d03_HPS_FORMAT_FIGEXP M_FIG C_FIG O_LIThe apple maggot fly and its parasitoids exhibit the same three diapause phenotypes C_LIO_LIEach parasitoid wasp species exhibits different proportions of these phenotypes C_LIO_LIUtetes canaliculatus and Diachasma alloeum are freeze-avoidant, like their host fly C_LIO_LIThese wasps and flies survive to similarly extreme low temperatures (c. -20{degrees}C) C_LIO_LIEach wasp species survives prolonged exposure to mild chilling (4{degrees}C) similarly well C_LI

physiology↗

bioRxiv2022

Simulated climate change causes asymmetric responses in insect life history timing potentially disrupting a classic ecological speciation system

Climate change may alter phenology within populations with cascading consequences for community interactions and on-going evolutionary processes. Here, we measured the response to climate change in two sympatric, recently diverged (~170 years) populations of Rhagoletis pomonella flies specialized on different host fruits (hawthorn and apple) and their parasitoid wasp communities. We tested whether warmer temperatures affect dormancy regulation and its consequences for synchrony across trophic levels and temporal isolation between divergent populations. Under warmer temperatures, both fly populations developed earlier. However, warming significantly increased the proportion of maladaptive pre-winter development in apple, but not hawthorn, flies. Parasitoid phenology was less affected, potentially generating ecological asynchrony. Observed shifts in fly phenology under warming may decrease temporal isolation, potentially limiting on-going divergence. Our findings of complex sensitivity of life-history timing to changing temperatures predict that coming decades may see multifaceted ecological and evolutionary changes in temporal specialist communities.

ecology↗

bioRxiv2022

Transcriptomic and functional genetic evidence for distinct ecophysiological responses across complex life cycle stages

Organisms with complex life cycles demonstrate a remarkable ability to change their phenotypes across development, presumably as an evolutionary adaptation to developmentally variable environments. Developmental variation in environmentally sensitive performance, and thermal sensitivity in particular, has been well documented in holometabolous insects. For example, thermal performance in adults and juvenile stages exhibit little genetic correlation (genetic decoupling) and can evolve independently, resulting in divergent thermal responses. Yet, we understand very little about how this genetic decoupling occurs. We tested the hypothesis that genetic decoupling of thermal physiology is driven by fundamental differences in physiology between life stages, despite a potentially conserved Cellular Stress Response. We used RNAseq to compare transcript expression in response to a cold stressor in Drosophila melanogaster larvae and adults and used RNAi (RNA interference) to test whether knocking down nine target genes differentially affected larval and adult cold tolerance. Transcriptomic responses of whole larvae and adults during and following exposure to -5{degrees}C were largely unique both in identity of responding transcripts and in temporal dynamics. Further, we found no relationship between stage-specificity and tissue-specificity of transcripts, suggesting that the differences are not simply driven by differences in tissue composition across development. In addition, RNAi of target genes resulted in largely stage-specific and sometimes sex-specific effects on cold tolerance. The combined evidence suggests that thermal physiology is largely stage-specific at the level of gene expression, and thus natural selection may be acting on different loci during the independent thermal adaptation of different life stages. Summary StatementRNAseq and gene knockout via transgenic RNAi lines suggest that physiological responses to low temperatures are largely distinct across life stages of the fly Drosophila melanogaster.

evolutionary biology↗

bioRxiv2020

The genomics of trait combinations and their influence on adaptive divergence

Understanding rapid adaptation requires quantifying natural selection on traits and elucidating the genotype-phenotype relationship for those traits. However, recent studies have often failed to predict the direction of adaptive allelic variation in natural populations from laboratory studies. Here, we test for genomic signatures of genetic correlations to illustrate how multifarious, correlational selection may drive counterintuitive patterns of population divergence in the apple maggot fly, Rhagoletis pomonella (Diptera: Tephritidae). Apple-infesting populations with relatively early emerging adults have recently evolved from hawthorn-infesting populations consisting of relatively later emerging adults. Multiple studies have reported a paradoxical relationship between population differentiation and seasonal timing, as determined by the timing of diapause termination; alleles associated with late termination occur at higher frequencies in the earlier emerging apple-infesting populations compared to hawthorn-infesting populations. We present evidence that historical selection on diapause termination and another trait, initial diapause intensity, over geographic gradients generated genetic correlations between the traits in a direction antagonistic to contemporary selection on apple-infesting populations. Single nucleotide polymorphism in genomic regions of high linkage disequilibrium associated strongly with diapause termination and intensity, population divergence, geography, and evolutionary responses in laboratory selection experiments. These associations were consistent with geographically variable selection and with correlated evolutionary responses driving higher frequencies of late-associated alleles in the early emerging apple race. In contrast, loci associated only with diapause termination showed the expected pattern (more early-associated alleles in the apple race) in half of the population pairs. Our results suggest that selection on loci demonstrating antagonistic pleiotropy may often shape genomic footprints of rapid adaptation.

evolutionary biology↗

bioRxiv2020

A rapidly evolved shift in life history timing during ecological speciation is driven by the transition between developmental phases

For insect species in temperate environments, seasonal timing is often governed by the regulation of diapause, a complex developmental program that allows insects to weather unfavorable conditions and synchronize their lifecycles with available resources. Diapause consists of a series of phases that govern initiation, maintenance, and termination of this developmental pathway. The evolution of insect seasonal timing depends in part on how these phases of diapause development and post-diapause development interact to affect variation in phenology. Here, we dissect the physiological basis of a recently evolved phenological shift in Rhagoletis pomonella (Diptera: Tephritidae), a model system for ecological divergence. A recently derived population of R. pomonella shifted from specializing on native hawthorn fruit to earlier fruiting introduced apples, resulting in a 3-4 week shift in adult emergence timing. We tracked metabolic rates of individual flies across post-winter development to test which phases of development may act either independently or in combination to contribute to this recently evolved divergence in timing. Apple and hawthorn flies differed in a number of facets of their post-winter developmental trajectories. However, divergent adaptation in adult emergence phenology in these flies was due almost entirely to the end of the pupal diapause maintenance phase, with post-diapause development having a very small effect. The relatively simple underpinnings of variation in adult emergence phenology suggest that further adaptation to seasonal change in these flies for this trait might be largely due to the timing of diapause termination unhindered by strong covariance among different components of post-diapause development. Data accessibilityAll data (in the form of tables of all metabolic rate measurements for all individual flies in the study) will be available on DRYAD when the manuscript is published.

evolutionary biology↗