Biology subjects

Marshall, K. E.

Publications and source records attributed to Marshall, K. E..

At least 19 recordsLinked to original sources

bioRxiv2026

Acclimation to thermal variability increases the intensity of activity and alters the activity window in the temperate dung beetle Onthophagus taurus

O_LIEctotherms in thermally variable environments mediate energy expenditure through both physiological and behavioural responses. However, many studies focus on constant temperature acclimation, and few consider behaviour and physiology in unison. It is unclear how acclimation to thermal variability affects locomotory choices, activity timing, and performance across daily thermal cycles. C_LIO_LIWe investigated the effects of thermal variability in the temperate dung beetle Onthophagus taurus. Following acclimation to a low amplitude (22{degrees}C {+/-} 2{degrees}C) or a high amplitude (22{degrees}C {+/-} 10{degrees}C) temperature regime, we measured behaviour and metabolic rate across temperatures. We hypothesised that O. taurus adjusts its locomotive strategy and search window when kept in high amplitude fluctuating temperatures to reduce energy loss associated with high temperature exposure. C_LIO_LIWe found that differences in energy expenditure were determined by propensity for flight which differed between acclimation treatments, particularly at intermediate temperatures. We also found that, following acclimation to a high amplitude of thermal variability, O. taurus exhibited a greater intensity of activity over a narrower window of time, and O. taurus acclimated to a low amplitude of thermal variability showed nocturnal activity. C_LIO_LIWe then used the data to model activity through the growing season over five years. Biophysical models were built using NicheMapR Microclimate and Ectotherm functions to test the length of potential searching time across seasons, the temperatures individuals are exposed, and locomotive strategy. Model outputs showed that acclimation to higher amplitudes of thermal variability increased accumulated degree-hours of activity relative to the low variability acclimation group. Individuals acclimated to higher amplitudes of thermal variability showed greater accumulated degree-hours in spring and fall, but exhibited shorter periods of activity during summer, with the model predicting increased opportunities for flight. Comparatively, O. taurus from the low variability acclimation treatment showed increased night activity in summer but did not fly. C_LI

physiology↗

bioRxiv2025

A proteomic analysis of the PHF-forming tau fragment (tau297-391) following uptake into differentiated human neuronal SHSY5Y cells

Tau self-assembly and intracellular deposition is associated with a group of neurodegenerative diseases called tauopathies, which include Alzheimers disease (AD) and Picks disease. Here, we measured the proteome response in human neuronal cells (differentiated SH-SY5Y) following addition of a spontaneously amyloidogenic region of tau known as dGAE (tau297-391) which forms AD-like paired helical filaments in vitro and proteomic analysis showed increased endogenous tau expression. Further interactome analysis uncovered increased association between tau and proteins associated with nuclear chromatin, the nucleolus, and the spliceosome as well as the thiol-peroxidase, PRDX6 alongside an increase in reactive oxygen species (ROS). This work highlights a method to identify proteome pathways that may play an important role in the development of tau pathology.

cell biology↗

bioRxiv2025

The macroecology of immunity: predominant influence of climate on invertebrate immune response

The immune system is the primary defense against parasites. With the ever-increasing rate of disease, epidemiologic models considering geographic variation in immune responses could prove useful. Despite increasing interest in the macroecology of parasitism and infectious diseases, we know little about the macroecology of immune responses. Host characteristics, parasite exposure, and environmental factors can all affect immunity, but how these factors interact to shape spatial variation in the strength of immune responses remains unexplored. We captured odonates (dragonflies and damselflies) and their conspicuous ectoparasitic mites across a geographic area spanning the temperate and boreal forest biomes in eastern Canada. We then conducted immune response bioassays on 1,237 individuals from 63 odonate species. We used linear regressions and structural equation models to relate immune responses to host body size, parasite load, pH, temperature, and precipitation while accounting for evolutionary relationships among host species. We found significant differences in the strength of immune response among host individuals, and this variation was best explained by climatic conditions, specifically decreasing with precipitation and, to a lesser degree, temperature. While host species significantly differed in immune response strength, we found no effect of host body size, evolutionary relationships among hosts, or parasitism on immune response. Our study investigating the drivers of immune response across dozens of species spread across two biomes is the most comprehensive to date. Climatic conditions have a strong influence on host immune response, regardless of host characteristics or parasitism rates. In this specific case, strong immune responses were associated with low levels of annual precipitation, which could relate to the role of cuticular melanin content in desiccation resistance, and the melanin-based encapsulation response being a byproduct of this adaptation. A spatially-explicit understanding of the biological processes affecting immunity could improve epidemiological models of disease risk that inform disease management globally.

immunology↗

bioRxiv2025

ICE BINDING PROTEIN ACTIVITY IS COMMON AMONG TEMPERATE PACIFIC INTERTIDAL INVERTEBRATES

Intertidal invertebrates often adopt freeze tolerance as a strategy to survive winter low tides, but the physiological mechanisms by which intertidal species survive freezing are not well understood. Ice binding proteins (IBPs) may play an important role, but their occurrence throughout the intertidal zone worldwide is not well-catalogued. Here we survey species in the intertidal zone of Vancouver, BC to assess IBP activities and the possible role they play in freeze tolerance. We conducted targeted assays in multiple intertidal species to measure three distinct activities of IBPs: ice nucleation, ice recrystallization inhibition, and thermal hysteresis. We also exposed intertidal species to a cold exposure mimicking a freezing event in the intertidal and measured survival post-exposure. We found that IBP activity was widespread across intertidal species, and that species with the highest degree of freeze tolerance also display ice nucleating activity attributable to proteins. We also found that species that live in the high intertidal appear to show more IBP activity than species that live lower in the intertidal. This work significantly increases the number of known species containing IBPs and provides a framework for sampling new species for IBP activity in the intertidal and elsewhere.

zoology↗

bioRxiv2025

Leveraging synthetic data produced from museum specimens to train adaptable species classification models

Computer vision has increasingly shown potential to improve data processing efficiency in ecological research. However, training computer vision models requires large amounts of high-quality, annotated training data. This poses a significant challenge for researchers looking to create bespoke computer vision models, as substantial human resources and biological replicates are often needed to adequately train these models. Synthetic images have been proposed as a potential solution for generating large training datasets, but models trained with synthetic images often have poor generalization to real photographs. Here we present a modular pipeline for training generalizable classification models using synthetic images. Our pipeline includes 3D asset creation with the use of 3D scanners, synthetic image generation with open-source computer graphic software, and domain adaptive classification model training. We demonstrate our pipeline by applying it to skulls of 16 mammal species in the order Carnivora. We explore several domain adaptation techniques, including maximum mean discrepancy (MMD) loss, fine-tuning, and data supplementation. Using our pipeline, we were able to improve classification accuracy on real photographs from 55.4% to a maximum of 95.1%. We also conducted qualitative analysis with t-distributed stochastic neighbor embedding (t-SNE) and gradient-weighted class activation mapping (Grad-CAM) to compare different domain adaptation techniques. Our results demonstrate the feasibility of using synthetic images for ecological computer vision and highlight the potential of museum specimens and 3D assets for scalable, generalizable model training.

bioinformatics↗

bioRxiv2025

Energetic consequences of single and repeated freezing in the intertidal mussel, Mytilus trossulus

The bay mussel, Mytilus trossulus, is a bivalve commonly found in intertidal zones along the west coast of North America which risks freezing during low tides in the winter. Previous work has shown that despite their freeze tolerance, freezing can still cause damage. Yet little is known about the energetic consequences of these freezing events. Here we measured the oxygen consumption of mussels before and after single and repeated freezing exposures across three seasons. We compared these responses to hypoxia exposures as tissues are not perfused while frozen which inhibits gas exchange. In general, we observed that mussels metabolic rates decreased immediately after a single freeze but recovers after 24 hours. By contrast, repeated freeze-thaws caused variable effects of metabolic rate, depending on the season of exposure. Overall, this suggests that the periods of recovery that occur between freeze-thaw cycles may mitigate freezing damage. We also found that hypoxia in general causes an increase in metabolic rate and may be associated with clearing oxygen debt. Therefore, the metabolic consequences after freezing are unlikely to be driven by hypoxia stress. Here we explore the energetic costs of freezing in M. trossulus informing future research directions into the mechanisms behind freeze tolerance.

zoology↗

bioRxiv2025

Inhibiting disulphide bonding in truncated tau297-391 results in enhanced self-assembly of tau into seed-competent assemblies.

Tau undergoes fibrillogenesis in a group of neurodegenerative diseases termed tauopathies. Each tauopathy is characterized by tau fibrils with disease-specific conformations, highlighting the complexity of tau self-assembly. This has led to debate surrounding the precise mechanisms that govern the self-assembly of tau in disease, especially the involvement of disulphide bonding (DSB) between cysteine residues. In this study, we use a truncated form of tau, dGAE, capable of forming filaments identical to those in disease. We reveal the impact of DSB in dGAE assembly and propagation by resolving the global mechanisms that dominate its assembly. We found evidence for surface-mediated secondary nucleation and fragmentation being active in dGAE assembly. The inhibition of DSB during dGAE assembly leads to an enhanced aggregation rate through a reduced lag phase, but with no effect on the global assembly mechanisms. We suggest this is due to the formation a dominant, seed-competent species in the absence of DSB that facilitates elongation and secondary nucleation resulting in enhanced assembly. In vitro seeding assays reveal the recruitment of endogenous tau in a cell model only when using dGAE species formed under conditions that inhibit DSB. Our results further support the use of the in vitro dGAE tau aggregation model for investigating the mechanism of tau assembly, the effect of varying conditions on tau assembly and how these conditions affect the resultant species. Further studies may utilise dGAE and its aggregates to investigate tau seeding, propagation and to highlight or test potential targets for therapies that reduce the spread of pathologic tau throughout the brain.

biochemistry↗

bioRxiv2024

Major changes in gene expression between strains of diapausing and non-diapause spruce budworm despite little evidence of genetic divergence

To survive harsh winter conditions, many insects enter a state of dormancy called diapause which allows them to withstand extreme temperatures and lack of food. When diapause is induced, insects enter a state of arrested development and low metabolic rate. Because diapause and environmental conditions are closely linked, variation within and between species in diapause induction, depth, and duration is extremely common. Studies investigating the genetic underpinnings of diapause tend to focus on either different populations and/or environmental variation, which runs the risk of confounding the genetic signal either due to isolation-by-distance or variation in environmental conditions. We use the eastern spruce budworm (Choristoneura fumiferana) to circumvent these issues and investigate within-population variation in diapause. C. fumiferana usually diapauses as second instar larvae, but a small subset of individuals does not diapause and instead continues through development. This non-diapause phenotype can be selected to create a non-diapause strain. Here, we present a chromosome-level assembly of such a non-diapause strain, and compare it to an earlier published genome assembly of the diapause strain. We did not find evidence of major chromosome rearrangements, indicating that the genetic variation between strains is likely small and multi-genic. Gene expression comparisons between the strains indicate major gene expression changes, where genes associated with glycolysis and environmental signaling processing increase in expression in the diapause strain. Lastly, we found that gene expression diverges halfway through the first instar, and not before, indicating that the signal to induce diapause happens early in the first instar. Significance statementThe ability to enter diapause is a crucial adaptation for many insects to survive cold winters. The genetic underpinnings of the diapause phenotype has been the target of many investigations. However, many of these studies focus on variation in diapause on between geographic regions or changes in environmental conditions, which can lead to confounding factors. Here, we focus on within-population variation in diapause in the eastern spruce budworm, with two strains established from the same source population that vary in their ability to induce diapause. We present a chromosome level assembly of the non-diapause strain, and report that genetic changes between the diapause and the non-diapause line are likely small and involve multiple loci. Gene expression differences were extensive, and mostly associated with mechanisms to avoid freezing. This work sets the stage to further investigate how minimal genetic changes can lead to large-scale phenotypic changes as impactful as diapause.

genetics↗

bioRxiv2024

The cold tolerance of the terrestrial slug, Ambigolimax valentianus

Terrestrial molluscs living in temperate and polar environments must contend with cold winter temperatures. However, the physiological mechanisms underlying the survival of terrestrial molluscs in cold environments and the strategies employed by them are poorly understood. Here we investigated the cold tolerance of Ambigolimax valentianus, an invasive, terrestrial slug that has established populations in Japan, Canada, and Europe. To do this, we acclimated A. valentianus to different environmental conditions (differing day lengths and temperatures), then exposed them to sub-zero temperatures and measured overall survival. Then, we measured low molecular weight metabolites using 1H NMR to see if they play a role in their cold tolerance as they do in other invertebrate species. We found that A. valentianus is not strongly freeze tolerant but do become more cold-hardy after acclimation to shorter day lengths. We also found that no metabolites were strongly upregulated in response to winter conditions despite the change in cold hardiness, and instead saw evidence of metabolic suppression leading up to winter such as formate and L-glutamine being supressed in winter conditions.

physiology↗

bioRxiv2024

Plasticity in cryoprotectant synthesis involves coordinated shunting away from pyruvate production

Insects living in temperate regions often accumulate a large amount of glycerol during winter to avoid freezing. This seasonal accrual of glycerol is generally produced from glycogen reserves through the pentose phosphate pathway. An alternative pathway to produce glycerol is through glycolysis, normally used for pyruvate production for eventual ATP synthesis. Aside from seasonal accumulation, some insects will also rapidly increase glycerol production as a short-term response to a sudden cold event, thereby increasing cold hardiness when necessary. In the eastern spruce budworm Choristoneura fumiferana, this plasticity in cold hardiness is locally adapted, where northern populations produce more glycerol upon cold shock. Here we investigate how glycerol is produced during the rapid plastic response to fluctuating cold conditions, and whether this pathway could be a target of local adaptation. After a period of repeated cold exposure, we found evidence of increased enzyme activity and increased mRNA abundance of several proteins associated with glycolysis, and a downregulation in expression of glucose-6-phosphate dehydrogenase, associated with pentose phosphate. Pyruvate production is prevented through downregulation of glyceraldehyde-3-phosphate dehydrogenase. We found higher overall enzyme activity and glycerol accumulation in a northern population from Alberta, although there was no evidence of an interaction effect between population and cold shock treatment. This is one the first studies to show a mechanistic basis of such plasticity in cold hardiness.

physiology↗

bioRxiv2024

A hybrid approach to invertebrate biomonitoring using computer vision and DNA metabarcoding

O_LIAutomated invertebrate classification using computer vision has shown significant potential to improve specimen processing efficiency. However, challenges such as invertebrate diversity and morphological similarity among taxa can make it difficult to infer fine-scale taxonomic classifications using computer vision. As a result, many invertebrate computer vision models are forced to make classifications at coarser levels, such as at family or order. C_LIO_LIHere we propose a novel modular method to combine computer vision and bulk DNA metabarcoding specimen processing pipelines to improve the accuracy and taxonomic granularity of individual specimen classifications. To improve specimen classification accuracy, our methods use multimodal fusion models that combine image data with DNA-based assemblage data. To refine the taxonomic granularity of the models classifications, our methods cross-references the classifications with DNA metabarcoding detections from bulk samples. We demonstrated these methods using a continental-scale, invertebrate bycatch dataset collected by the National Ecological Observatory Network. We also introduce the CV.eDNA R package, which aims to assist practitioners looking to implement our methods. C_LIO_LIUsing our methods, we reached a classification accuracy of 79.6% across the 17 taxa using real DNA assemblage data, and 83.6% when the assemblage data was "error-free", resulting in a 2.2% and 6.2% increase in accuracy when compared to a model trained using only images. After cross-referencing with the DNA metabarcoding detections, we improved taxonomic granularity in up to 72.2% of classifications, with up to 5.7% reaching species-level. C_LIO_LIBy providing computer vision models with coincident DNA assemblage data, and refining individual classifications using DNA metabarcoding detections, our methods the potential to greatly expand the capabilities of biological computer vision classifiers. Our methods allow computer vision classifiers to infer taxonomically fine-grained classifications when it would otherwise be difficult or impossible due to challenges of morphologic similarity or data scarcity. These methods are not limited to terrestrial invertebrates and could be applied in any instance where image and DNA metabarcoding data are concurrently collected. C_LI

bioinformatics↗

bioRxiv2024

Temperature fluctuations influence predictions of landscape-scale patterns of spruce budworm defoliation

AimWhile many studies on ectotherm thermal tolerance consider temperature exposure, the frequency of temperature exposures is emerging as an important and generally overlooked driver of survival and fitness which may influence species ranges. We use a physiologically-informed species distribution model to evaluate the influence of temperature fluctuations on the historical distribution and intensity of defoliation of a Lepidopteran forest pest, and on predicted future defoliation. LocationEastern Canada. Time period2006-2016, projections to 2041-2070. Major taxa studiedChoristoneura fumiferana (Lepidoptera: Tortricidae, spruce budworm). MethodsWe combined publicly-available maps of spruce budworm-induced defoliation between 2006-2016 in the Canadian province of Quebec with climate, forest composition, and de novo temperature fluctuation predictors to train a species distribution model. Our model evaluated how predictor categories influence spruce budworm defoliation and compared these results to a model trained without temperature fluctuations. Additionally, we predicted future spruce budworm defoliation under 2041-2070 climate change conditions using the models trained with and without temperature fluctuation predictors to determine the impact of temperature fluctuations on future defoliation predictions. ResultsWe found that the inclusion of temperature fluctuation predictors improved model performance, and these predictors ranked highly in importance relative to predictors in other categories. The model trained with temperature fluctuation predictors also predicted vastly different defoliation distribution and severity across Quebec, Ontario, and Labrador than the model trained without them under future climate. Main conclusionsOur study reveals the previously overlooked importance of temperature fluctuations on landscape-scale spruce budworm defoliation and demonstrates the importance of including physiologically-informed predictors in species distribution models. It also provides a novel framework for including thermal variation in correlative species distribution models of ectotherms.

zoology↗

bioRxiv2023

Consideration of sex as a biological variable in diabetes research across twenty years

Sex differences exist in the risk of developing both type 1 and type 2 diabetes, and in the risk of developing diabetes-associated complications. Sex differences in glucose homeostasis, islet and {beta} cell biology, and peripheral insulin sensitivity have also been reported in multiple animals. To determine the degree to which biological sex has been addressed in published literature related to diabetes and insulin biology, we developed a scoring system to assess the inclusion of biological sex in papers related to these topics. We scored manuscripts published in Diabetes, published by the American Diabetes Association, as this journal focuses on diabetes and diabetes-related research. We scored papers published across three years within a 20-year period (1999, 2009, 2019), a timeframe that spans the introduction of funding agency and journal policies to improve the consideration of biological sex as a variable. Our analysis shows fewer than 15% of papers used sex-based analysis in even one figure across all study years, a trend that was reproduced across journal-defined categories of diabetes research (e.g., islet studies, signal transduction). Single-sex studies accounted for approximately 40% of all manuscripts, of which >87% used male subjects only. While we observed a modest increase in the overall inclusion of sex as a biological variable during our study period, our results highlight significant opportunities to improve consideration of sex as a biological variable in diabetes research. In particular, we show that journal policies represent one way to promote better consideration of biological sex as a variable. In the long term, improved practices will reveal sex-specific mechanisms underlying diabetes risk and complications, generating insights to support the development of sex-informed prevention and treatment strategies.

scientific communication and education↗

bioRxiv2022

Ocean acidification increases susceptibility to sub-zero air temperatures in ecosystem engineers (Mytilus sp.): a limit to poleward range shifts

Ongoing climate change has caused rapidly increasing temperatures, and an unprecedented decline in seawater pH, known as ocean acidification. Increasing temperatures are redistributing species towards higher and cooler latitudes which are most affected by ocean acidification. Whilst the persistence of intertidal species in cold environments is related to their capacity to resist sub-zero air temperatures, studies have never considered the interacting impacts of ocean acidification and freeze stress on species survival and distribution. A full-factorial experiment was used to study whether ocean acidification increases mortality in Mytilus spp. following sub-zero air temperature exposure. We examined physiological processes behind variation in freeze tolerance using 1H NMR metabolomics, analyses of fatty acids, and amino acid composition. We show that low pH conditions (pH = 7.5) significantly decrease freeze tolerance in both intertidal and subtidal populations of Mytilus spp. Under current day pH conditions (pH = 7.9), intertidal M. trossulus were more freeze tolerant than subtidal M. trossulus and M. galloprovincialis. Opposite, under low pH conditions, subtidal M. trossulus was more freeze tolerant than the other groups. We observed a marked shift from negative to positive metabolite-metabolite correlations across species under low pH conditions, but there was no evidence that the concentration of individual metabolites or amino acids affected freeze tolerance. Finally, pH-induced changes in the composition of cell membrane phospholipid fatty acids had no effect on survival. These results suggest that ocean acidification can offset the poleward expanding facilitated by warming, and that reduced freeze tolerance could result in a niche squeeze if temperatures become lethal at the equatorward edge.

ecology↗

bioRxiv2022

Dityrosine cross-links are present in Alzheimer's disease-derived tau oligomers and paired helical filaments (PHF) which promotes the stability of PHF-core tau (297-391) in vitro.

A characteristic hallmark of Alzheimers Disease (AD) is the pathological aggregation and deposition of tau into paired helical filaments (PHF) in neurofibrillary tangles (NFTs). Oxidative stress is an early event during AD pathogenesis and is associated with tau-mediated AD pathology. Oxidative environments can result in the formation of covalent dityrosine crosslinks that can increase protein stability and insolubility. Dityrosine cross-linking has been shown to occur in vivo in A{beta} plaques and -synuclein aggregates in Lewy bodies, and this modification may increase the insolubility of these aggregates and their resistance to degradation. Using the PHF-core tau fragment (residues 297 - 391) as a model, we have previously demonstrated that dityrosine formation traps tau assemblies to reduce further elongation. However, it is unknown whether dityrosine crosslinks are found in tau deposits in vivo in AD and its relevance to disease mechanism is unclear. Here, using transmission electron microscope (TEM) double immunogold-labelling, we reveal that neurofibrillary NFTs in AD are heavily decorated with dityrosine crosslinks alongside tau. Single immunogold-labelling TEM and fluorescence spectroscopy revealed the presence of dityrosine on AD brain-derived tau oligomers and fibrils. Using the tau (297-391) PHF-core fragment as a model, we further showed that prefibrillar tau species are more amenable to dityrosine crosslinking than tau fibrils. Dityrosine formation results in heat and SDS stability of oxidised prefibrillar and fibrillar tau assemblies. This finding has implications for understanding the mechanism governing the insolubility and toxicity of tau assemblies in vivo.

biochemistry↗

bioRxiv2022

Transcriptome-wide patterns reveal conserved and population-specific responses to increasing acclimation temperatures in developing lake sturgeon (Acipenser fulvescens)

Rising mean and variance in temperatures elevate threats to endangered freshwater species such as lake sturgeon, Acipenser fulvescens. Previous research demonstrated that higher temperatures during development result in physiological consequences for lake sturgeon populations throughout Manitoba, Canada, with alteration of metabolic rate, thermal tolerance, transcriptional responses, growth, and mortality. We acclimated lake sturgeon (30 - 60 days post fertilization, a period of high mortality) from northern and southern populations (56{degrees} 02' 46.5'' N, 96{degrees} 54' 18.6'' W and 50{degrees} 17' 52'' N, 95{degrees} 32' 51'' W respectively, separated by approximately 650 km) within Manitoba to current (summer highs of 20-23{degrees}C) and future projected (+2-3{degrees}C) environmental temperatures of 16, 20, and 24{degrees}C for 30 days, and measured gill transcriptional responses using RNAseq. Transcripts revealed SNPs consistent with genetically distinct populations and transcriptional responses altered by acclimation temperature. There were a higher number of differentially expressed transcripts observed in the southern, compared to the northern, population as temperatures increased, indicating enhanced transcriptional plasticity. Both lake sturgeon populations responded to elevated acclimation temperatures by downregulating the transcription of genes involved in protein synthesis and energy production. Further, there were population-specific thresholds for the downregulation of processes promoting transcriptional plasticity as well as mitochondrial function as the northern population showed decreases at 20{degrees}C, while this capacity was not diminished until 24{degrees}C in the southern population. These transcriptional responses highlight the molecular impacts of increasing temperatures for divergent lake sturgeon populations during vulnerable developmental periods and the critical influence of transcriptome plasticity on acclimation capacity.

molecular biology↗

bioRxiv2022

Proteostasis in ice: The role of heat shock proteins and ubiquitin in the freeze tolerance of the intertidal mussel, Mytilus trossulus

The bay mussel, Mytilus trossulus, is one of the few animals that can survive internal ice formation. Freeze tolerant intertidal animals, like M. trossulus, may freeze and thaw many times during the winter, depending on air and ocean temperatures. Freezing can cause protein denaturation, leading to an induction of the heat shock response with expression of proteins like HSP70, and an increase in ubiquitin conjugated proteins. There has been little work on the mechanisms of freeze tolerance in intertidal species, limiting our understanding of this survival strategy. Additionally, this limited research has focused solely on the effects of single freezing events, but the act of repeatedly crossing the freezing threshold may present novel physiological or biochemical stressors that have yet to be discovered. We predicted that repeated freeze exposures would increase mortality, upregulate HSP70 expression, and increase ubiquitin conjugates in mussels, relative to single, prolonged freeze exposures. Mytilus trossulus from Vancouver, Canada were repeatedly frozen for a combination of 1 x 8 hours, 4 x 2 hours, or 2 x 4 hours. We then compared mortality, HSP70 expression, and ubiquitin quantity across experimental groups. We found a single 8-hour freeze caused significantly more mortality than repeated freeze-thaw cycles. We also found that HSP70 and ubiquitin expression was upregulated exclusively after freeze-thaw cycles, suggesting that freeze-thaw cycles offer a period of damage repair between freezes. This indicates that freeze-thaw cycles, which happen naturally in the intertidal, are crucial for M. trossulus survival in sub-zero temperatures.

biochemistry↗

bioRxiv2022

Population demography maintains biogeographic boundaries

Global biodiversity is organized into biogeographic regions that comprise distinct biotas. The contemporary factors maintaining differences in species composition between biogeographic regions are poorly understood. Given the evidence that populations with sufficient genetic variation can adapt to fill new habitats, it is surprising that we do not see more homogenization of species assemblages among regions. Theory suggests that the expansion of populations across biogeographic transition zones could be limited by environmental gradients that affect population demography in ways that could limit adaptive capacity, but this has not been empirically explored. Using three independently curated data sets describing continental patterns of mammalian demography and population genetics, we show that populations closer to biogeographic transition zones have lower effective population sizes and genetic diversity, and are more genetically differentiated. These patterns are consistent with reduced adaptive capacity near biogeographic transition zones. The consistency of these patterns across mammalian species suggests they are stable, predictable, and generalizable in their contribution to long-term limits on expansion and homogenization of biodiversity across biogeographic transition zones. Understanding the contemporary processes acting on populations that maintain differences in the composition of regional biotas is crucial for our basic understanding of the current and future organization of global biodiversity. The importance of contemporary, population-level processes on the maintenance of global biogeographic regions suggests that biogeographic boundaries are susceptible to environmental perturbation associated with human-caused global change.

ecology↗