Biology subjects

Toxopeus, J.

Publications and source records attributed to Toxopeus, J..

11 recordsLinked to original sources

bioRxiv2026

Freeze tolerance of a beneficial lady beetle, Hippodamia convergens

The convergent lady beetle Hippodamia convergens is widespread in the Americas and considered an important beneficial insect due to its use in pest control. Early work on this species characterized the beetles as freeze-avoidant (freeze-intolerant), suggesting they survive low winter temperatures by physiologically preventing ice formation to temperatures as low as -15{degrees}C. Here, we show that H. convergens can be freeze-tolerant if ice formation occurs at relatively high temperatures. There was 100% survival following inoculative freezing at -0.5{degrees}C and exposure to -3{degrees}C for 20 hours, as well as freezing that spontaneously occurred in fed beetles exposed to -4{degrees}C for 4 hours. Males exposed to 0{degrees}C or -4{degrees}C for 4 hours had similar mating behaviours (latency to first mating, copulation duration) as control beetles exposed to 4{degrees}C, although sample sizes were too small to determine whether freezing itself had an effect on these behaviours. Several putative cryoprotectants were detected in fat body tissue of H. convergens: glycerol, proline, trehalose, and myo-inositol - in order of abundance. Exposure to -3{degrees}C for 20 hours, whether frozen or unfrozen, did not statistically affect cryoprotectant accumulation, although there was a trend towards increased glycerol following freezing. This study is the first to describe inoculative freeze tolerance in a lady beetle and establishes a baseline for future studies that examine the mechanisms underlying this freeze tolerance and the effects of freezing on reproductive behaviour. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=69 SRC="FIGDIR/small/744689v1_ufig1.gif" ALT="Figure 1"> View larger version (16K): org.highwire.dtl.DTLVardef@1c0382org.highwire.dtl.DTLVardef@12a5932org.highwire.dtl.DTLVardef@145f4adorg.highwire.dtl.DTLVardef@1c2cb22_HPS_FORMAT_FIGEXP M_FIG C_FIG O_LIHippodamia convergens can tolerate freezing at high subzero temperatures C_LIO_LIMating behaviour of males is normal after chilling or freezing C_LIO_LICryoprotectant accumulation may support overwintering survival C_LI

zoology↗

bioRxiv2026

Overwintering under the ice: seasonal shifts in cold and hypoxia stress physiology of three winter-active pond insects

Winter poses harsh physiological challenges for insects living in temperate ponds due to the combination of low temperatures and reduced oxygen levels (hypoxia). Despite these stressors, water boatmen (Hesperocorixa sp.), backswimmers (Notonecta sp.) and diving beetles (Laccophilus maculosus) remain active year-round in eastern Nova Scotia, including in ice- covered ponds. However, the underlying mechanisms that allow pond insects to survive overwintering have not been widely studied. We hypothesized that cold and hypoxia tolerance would improve from September to March in these insects, with changes in whole-animal and biochemical correlates of tolerance to both stressors. We collected insects from the field and stocked them in outdoor freshwater mesocosms. Every two months, between September 2023 and April 2024, we characterized whole animal responses and biochemical changes. Whole insect cold tolerance assays indicated a trend of improved ability to sustain voluntary muscle control (CTmin) at lower temperatures in winter-collected insects and higher internal fluid freezing temperatures (SCP). There were no changes in whole animal correlates of hypoxia tolerance over time (surface respiration frequency, submersion and surface time). Potential cryoprotectants like proline, myo-inositol and trehalose increased in concentration in multiple insect taxa during winter but were relatively low compared to terrestrial insect studies. As lactate dehydrogenase activity did not change, there is little evidence that the insects experienced functional hypoxia sufficient to induce anaerobic metabolism. Overall, this research has established a baseline cold and hypoxia tolerance dataset in understudied pond insects. Summary StatementPond insects remain active during low temperature and low oxygen conditions associated with ice cover in winter, supported by physiological and biochemical changes.

zoology↗

bioRxiv2025

The cold tolerance of an adult winter-active stonefly: How Allocapnia pygmaea (Plecoptera: Capniidae) avoids freezing in Nova Scotian winters

Allocapnia pygmaea Burmeister (Plecoptera: Capniidae) is a winter-active stonefly in North America. Despite the adults winter emergence, little is documented about the cold tolerance and cryoprotective biochemistry of A. pygmaea. To better understand the cold tolerance of this winter-active stonefly, we collected adult A. pygmaea in Antigonish, NS during March or April in both 2023 and 2024. Following different cold exposures, we measured the lower limits of activity (-8.9 {degrees}C) and the temperature at which internal freezing occurs (-11.9 {degrees}C), and confirmed that A. pygmaea could survive subzero temperatures unless they froze. We also assayed the following putative cryoprotectants: proline, glycerol, myo-inositol, trehalose, and glucose in control (field-collected) and cold-shocked groups. We detected little effect of cold shock on most cryoprotectants, except for the polyols glycerol and myo-inositol, which decreased in concentration following cold shock. These findings improve our current understanding of Capniid cold tolerance, confirming that A. pygmaea uses a freeze-avoidant strategy, and lay a foundation for future studies on how they may use cryoprotectants for winter-activity.

zoology↗

bioRxiv2025

Tissue- and temperature-dependent expression, enzyme activity, and RNAi knockdown of Catalase in a freeze-tolerant insect

Organisms that overwinter in temperate climates may experience freezing and freezing-induced oxidative stress during winter. While many insect species can survive freezing, molecular tools such as RNA interference (RNAi) or CRISPR have not been used to understand the physiological mechanisms underlying freeze tolerance. The spring field cricket Gryllus veletis can survive freezing following a 6-week fall-like acclimation. We used RNAi of an antioxidant enzyme in G. veletis to test the hypothesis that minimizing oxidative stress is important for freeze tolerance. In fat body tissue, Catalase mRNA abundance and enzyme activity increased during the acclimation that induces freeze tolerance. Other tissues such as midgut and Malpighian tubules had more stable or lower Catalase expression and activity during acclimation. In unacclimated (freeze-intolerant) crickets, RNA interference (RNAi) effectively knocked down production of the Catalase mRNA and protein in fat body and midgut, but not Malpighian tubules. In acclimated (freeze-tolerant) crickets, RNAi efficacy was temperature-dependent, functioning well at warm (c. 22{degrees}C) but not cool (15{degrees}C or lower) temperatures. This highlights a challenge of using RNAi in cold-acclimated organisms, as they may need to be warmed up for RNAi to work, potentially affecting their stress physiology. Knockdown of Catalase via RNAi in acclimated crickets also had no effect on the ability of the crickets to survive a mild freeze treatment, suggesting that Catalase may not be necessary for freeze tolerance. Our study is the first to demonstrate that RNAi is possible in a freeze-tolerant insect, but further research is needed to examine whether other genes and antioxidant molecules are important in freeze tolerance of G. veletis. HighlightsO_LICatalase expression and activity are elevated in freeze-tolerant cricket fat body C_LIO_LIRNAi knocks down Catalase in fat body and midgut at a warm temperature (22{degrees}C) C_LIO_LIRNAi is not effective at a cool temperature (15{degrees}C) that preserves freeze tolerance C_LIO_LICatalase knockdown has no impact on survival of a mild freeze treatment C_LIO_LIThe role of antioxidants in freeze tolerance warrants further study C_LI Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=77 SRC="FIGDIR/small/637938v1_ufig1.gif" ALT="Figure 1"> View larger version (20K): org.highwire.dtl.DTLVardef@1c4d9b8org.highwire.dtl.DTLVardef@b1c304org.highwire.dtl.DTLVardef@7a421eorg.highwire.dtl.DTLVardef@8af62f_HPS_FORMAT_FIGEXP M_FIG C_FIG

physiology↗

bioRxiv2024

Freeze-tolerant crickets fortify their actin cytoskeleton in fat body tissue

Animals that overwinter in temperate climates must prevent or repair damage to their cells to survive winter, but we know little about how they protect cellular structure at the cytoskeletal level. Both chilling (no ice formation) and freezing (ice formation) are hypothesized to cause substantial challenges to cell structure and the cytoskeleton. The spring field cricket Gryllus veletis becomes freeze-tolerant following a 6-week acclimation to fall-like conditions, during which they differentially express multiple cytoskeleton-related genes. We tested the hypothesis that G. veletis alter their cytoskeleton during acclimation to support maintenance of cytoskeletal structure during freezing and thawing. We used immunocytochemistry and confocal microscopy to characterize changes in microfilaments (F-actin, a polymer of G-actin) and microtubules (a polymer of - and {beta}-tubulin) in three tissues. While we saw no effect of acclimation on microtubules, crickets increased the abundance of microfilaments in fat body and Malpighian tubules. When we chilled or froze these freeze-tolerant crickets, there was no apparent damage to the actin or tubulin cytoskeleton in fat body, but there was decreased cytoskeleton abundance in Malpighian tubules. When we froze freeze-intolerant (unacclimated) crickets, microfilament abundance decreased in fat body tissue, while microfilaments were unaffected by chilling to the same subzero temperature. Our study shows that freeze-tolerant crickets are able to prevent or rapidly repair ice-induced damage to the actin cytoskeleton in fat body, likely due to preparatory changes in advance of freezing - i.e., during acclimation. We suggest future directions examining the mechanisms that underlie these structural changes. Summary StatementFreeze-tolerant crickets (Gryllus veletis) modify their actin cytoskeleton in select tissues to prevent freeze-induced cellular damage, while freeze-intolerant crickets of the same species experience irreparable cytoskeleton damage during freezing.

cell biology↗

bioRxiv2024

HSP70 is upregulated after heat but not freezing stress in the freeze-tolerant cricket Gryllus veletis

Heat shock proteins (HSPs) are well known to prevent and repair protein damage caused by various abiotic stressors, but their role in low temperature and freezing stress is not well-characterized compared to other thermal challenges. Ice formation in and around cells is hypothesized to cause protein damage, yet many species of insects can survive freezing, suggesting HSPs may be an important mechanism in freeze tolerance. Here, we studied HSP70 in a freeze-tolerant cricket Gryllus veletis to better understand the role of HSPs in this phenomenon. We measured expression of one heat-inducible HSP70 isoform at the mRNA level (using RT-qPCR), as well as the relative abundance of total HSP70 protein (using semi-quantitative Western blotting), in five tissues from crickets exposed to a survivable heat treatment (2 h at 40{degrees}C), a 6-week fall-like acclimation that induces freeze tolerance, and a survivable freezing treatment (1.5 h at -8{degrees}C). While HSP70 expression was upregulated by heat at the mRNA or protein level in all tissues studied (fat body, Malphigian tubules, midgut, femur muscle, nervous system ganglia), no tissue exhibited HSP70 upregulation within 2 - 24 h following a survivable freezing stress. During fall-like acclimation to mild low temperatures, we only saw moderate upregulation of HSP70 at the protein level in muscle, and at the RNA level in fat body and nervous tissue. Although HSP70 is important for responding to a wide range of stressors, our work suggests that this chaperone may be less critical in the preparation for, and response to, moderate freezing stress. HighlightsO_LIHeat shock protein 70 (HSP70) may not contribute substantially to freeze tolerance C_LIO_LIHeat stress caused HSP70 mRNA and protein upregulation in the spring field cricket C_LIO_LIAcclimation prior to freezing was correlated with slight HSP70 upregulation C_LIO_LIHSP70 was not upregulated after freezing in this freeze-tolerant insect C_LIO_LIFurther work is needed to determine whether freezing causes protein damage C_LI Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=72 SRC="FIGDIR/small/621172v1_ufig1.gif" ALT="Figure 1"> View larger version (18K): org.highwire.dtl.DTLVardef@170fda7org.highwire.dtl.DTLVardef@11cf432org.highwire.dtl.DTLVardef@1e41be9org.highwire.dtl.DTLVardef@e46c4d_HPS_FORMAT_FIGEXP M_FIG C_FIG

physiology↗

bioRxiv2024

Invasive adult jumping worms in Atlantic Canada are chill-susceptible

The jumping worm Amynthas tokioensis is invasive in North America, and it has been expanding its range northward in recent years. Because low temperatures typically restrict the geographic distribution of organisms, our goal was to characterize the cold tolerance physiology of adult jumping worms from a site in New Brunswick, Canada (c. 45{degrees}N), with the intent of better understanding their geographic range limits. Most of our experiments supported the conclusion that these worms are chill-susceptible: they die during or after exposure to relatively mild low temperatures. When gradually cooled, adult worms lost neuromuscular coordination at approximately 0 {degrees}C and froze at a mean temperature of -4.5 {degrees}C. They did not survive freezing and showed poor survival following 1 h exposures to 0 {degrees}C and subzero temperatures. At higher mild temperatures (5 {degrees}C), the worms could survive short (up to 6 h) but not long (e.g., 48 h) chilling durations. We attempted to induce improved cold tolerance via a five-week gradual acclimation to fall-like temperatures, but fall-acclimated worms showed poor survival during and after this acclimation. Acclimation also did not induce accumulation of glucose, a typical cryoprotectant in earthworms. We suggest that A. tokioensis can likely persist wherever the growing season is sufficiently warm and long enough for the adults to mature, reproduce, and lay cocoons prior to the chilling temperatures associated with early fall. Future work examining the cold tolerance of the overwintering cocoons will be important for fully understanding the northern range limits of these jumping worms.

zoology↗

bioRxiv2023

Conserved cold tolerance of Rhagoletis species from different host fruits, elevations in Colorado, USA

Understanding and characterizing how insects tolerate low temperatures is important for predicting their overwintering survival and subsequent geographic spread. This study characterized the cold tolerance of two members of the Rhagoletis genus in Colorado, U.S.A. Pupae were collected from infested fruit in late summer and early fall. For the first time, we show that the rosehip fly Rhagoletis basiola is freeze-avoidant; overwintering pupae could supercool to temperatures as low as -26{degrees}C and survive. Interestingly, the temperature at which ice forms (supercooling point; SCP) did not vary between R. basiola at high (c. 2900 m above sea level) and lower (c. 1650 m a.s.l.) elevations. We also report the apple maggot Rhagoletis pomonella infesting an unusual host fruit, the Dolgo crabapple, in close proximity to infested hawthorn trees. R. pomonella infesting hawthorn fruits and crabapples had similar SCPs, and survived temperatures as low as -21{degrees}C. Pupae from both host fruits also survived prolonged exposure (2 weeks or more) to mild low temperatures (0 to -5{degrees}C). Further study into the mechanisms underlying the impressive and conserved cold tolerance of R. pomonella and R. basiola is an interesting avenue for future research.

zoology↗

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

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↗