Biology subjects

Hahn, D. A.

Publications and source records attributed to Hahn, D. A..

6 recordsLinked to original sources

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↗

bioRxiv2024

SUPPRESSION OF AEDES AEGYPTI BY STERILE INSECT TECHNIQUE (SIT) ON CAPTIVA ISLAND, FLORIDA, USA FROM 2020 TO 2022

Aedes aegypti, an aggressive nuisance biter and the primary vector for numerous arboviruses, such as chikungunya, dengue, and Zika, presents significant control challenges due to its ability to thrive in urban environments, escapes insecticide treatment by using cryptic resting and oviposition sites, and development of resistance to chemical mosquito control products being used routinely. To test a new approach in their integrative mosquito management toolbox. From 2020 to 2022, the Lee County Mosquito Control District (LCMCD) employed the Sterile Insect Technique (SIT) to test a new approach in its integrated mosquito management toolbox, targeting the population suppression of Ae. aegypti on Captiva Island, Florida. Over 24.1 million sterile males were released across three phases, covering up to 142 hectares. The study demonstrated a population reduction of up to 79% in wild adults and a 59% decline in egg densities in the primary intervention area. While population control was successful, an influx of wild females from untreated zones posed ongoing challenges to complete suppression in areas close to non-intervention areas. This supported a need for an area-wide integrated pest management (AW-IPM) approach. These results underscore SITs potential as a critical tool in integrated mosquito management strategies and emphasize practical application.

ecology↗

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↗

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↗