Biology subjects

Weber, J. N.

Publications and source records attributed to Weber, J. N..

At least 19 recordsLinked to original sources

bioRxiv2026

Constitutive and inducible fibrosis explain immune variation among threespine stickleback populations

Understanding how immune variation arises in natural populations requires disentangling the relative contributions of host genetic differences, environmental variation, and parasite effects, which is rarely possible in wild systems. Threespine stickleback populations vary in their use of intraperitoneal fibrosis as a defense against the helminth parasite Schistocephalus solidus, providing a natural system to study the genetic and ecological drivers of immune variation. We combined a 46-lake field survey with common garden experiments on 20 representative populations exposed to multiple parasite genotypes to test whether population differences in fibrosis persist under controlled conditions and whether they depend on parasite genotype or lake ecology. Fibrosis variation was strongly heritable, with both constitutive and inducible components persisting under common garden conditions. In contrast, parasite genotype had only a weak effect on fibrosis responses. Moreover, inducible fibrosis covaried with lake environmental conditions, with populations from more eutrophic-like lakes exhibiting stronger responses than those from more oligotrophic-like lakes. Together, these results reveal ecologically structured divergence in heritable immune responses among natural populations.

evolutionary biology↗

bioRxiv2026

Intrinsic fitness differences outweigh environmental matching in shaping introduction outcomes in nature

Species introductions and transplants offer powerful contexts to understand evolutionary patterns and processes, and they are increasingly critical for conservation. However, introduction success varies widely, and predicting outcomes remains challenging. Introducing multiple source populations should increase the chance of success, while also providing an opportunity to explore the factors that predict success of individual source populations in the same environment. We used replicated, mixed-population introductions of >12,000 threespine stickleback (Gasterosteus aculeatus) to test whether source population success could be predicted by environmental matching between source and recipient environments and/or by intrinsic source population characteristics. We introduced four to eight source populations of stickleback into each of nine natural lakes and tracked their relative success over the following two years (up to two generations). Source population success was largely consistent across lakes, despite divergent environmental conditions. These results point to the importance of intrinsic source population characteristics rather than environmental matching in predicting introduction success in natural settings. Source populations that were consistently successful tended to have greater stress tolerance (mortality rate during translocation) and higher genetic diversity, though these relationships were not conclusive. Our study highlights the value of considering factors that generate fitness differences independent of environmental contexts in predicting ecological and evolutionary dynamics and planning conservation programs. Significance StatementPredicting which populations will succeed when introduced to new environments is a central challenge in ecology, evolution, and conservation. Environmental conditions are often assumed to be crucial in determining which populations succeed, given the expectation that populations preadapted to local conditions should perform best. We test this assumption by introducing >12,000 threespine stickleback fish from up to eight source populations into nine natural lakes spanning diverse environmental conditions. We show that the relative success of individual source populations was remarkably consistent across lakes and environmental conditions, indicating that some populations are intrinsically better suited to introductions. Our findings underscore the importance of considering intrinsic population characteristics alongside environmental conditions when predicting ecological and evolutionary outcomes and guiding conservation efforts.

evolutionary biology↗

bioRxiv2025

Lake size shapes the relationship between body mass and gut microbiota in threespine stickleback (Gasterosteus aculeatus)

Host-microbe interactions are shaped by both host and environmental factors. However, little is known about how host-microbe interactions vary across populations within a species. Here, we characterized the gut microbiota of 191 wild threespine stickleback fish (Gasterosteus aculeatus) from six populations from Alaskan lakes spanning a gradient of surface area. We tested how environmental context (lake size and ecotype) and host traits (sex, body mass, gravidity, Schistocephalus solidus (S. solidus) infection, and fibrosis) influence stickleback gut microbial composition using 16S rRNA gene sequencing. We found that the lake surface area strongly predicted fish gut microbial alpha diversity. Fish from intermediate-sized lakes harbored significantly more diverse microbiota than those from small and large lakes, independent of ecotype. Body mass was associated with gut microbial diversity. Model-predicted marginal effects from the mass and lake surface area interaction analysis showed that the association between fish mass and microbial alpha diversity was strongly negative in the smallest lakes, weakest in intermediate-sized lakes, and strongly positive in the largest lakes. In addition, sex and S. solidus infection were significantly associated with gut microbiota alpha and beta diversity, whereas fibrosis and gravidity showed minimal effects. Differential abundance analysis revealed lake size-dependent associations between body mass and individual taxa. Together, these results demonstrate that both habitat context and host variation interactively shape stickleback gut microbial communities in the wild. Integrating lake-level and individual-level analyses reveals how ecological setting modulates host-microbe associations, offering insights into the role of the gut microbiota in host adaptation and population divergence.

microbiology↗

bioRxiv2025

Heritable differences in metabolic stability underpin thermal tolerance of threespine stickleback (Gasterostues aculeatus) ecotypes

Understanding how organisms adapt to divergent thermal conditions can inform efforts to preserve biodiversity in a warming world. Change in aerobic scope (AS)-total energy available to perform tasks outside of homeostasis-is an ecologically relevant predictor of performance across a range of temperatures. Mathematical models suggest that the shape of AS-temperature curves should evolve depending on environmental heterogeneity, but few studies have tested whether this occurs at the intraspecific level. We examined AS-temperature associations across two ecotypes of threespine stickleback fish (Gasterosteus aculeatus), including both short- and long-term heat treatments. We predicted that fish from shallow, thermally dynamic lakes would display greater AS stability at high temperatures than residents of deep, thermally stable lakes. We also tested whether heat and AS are correlated with variation in a fibrotic immune response after exposure to the cestode Schistocephalus solidus. We found few heat-associated differences in condition or immunity, but fibrosis decreased AS. Additionally, limnetic AS declined with heat and this shift was correlated with mortality. In contrast, benthic ecotypes displayed remarkable stability in AS and survival across temperatures. Connecting intraspecific variation in AS with local thermal environments is a promising avenue for estimating, and potentially fostering, population resilience to warming climates.

evolutionary biology↗

bioRxiv2025

Heritable and environmental influences on innate immunity across three populations of threespine stickleback (Gasterosteus aculeatus)

Environmental variation plays a key role in immune development and function; factors such as pathogen exposure history, seasonality, and resource availability all affect an individuals immune phenotype. However, the relative contributions of heritable and non-heritable factors remain unclear for most immune phenotypes. We used three populations of threespine stickleback (Gasterosteus aculeatus) with heritable differences in immune function to investigate the relationship between immunity, genetic divergence, and the environment. To test for environmental effects on immunity, fish were raised in tanks with different flow rates (continuous or intermittent). After long-term acclimation to one tank environment, subsets of adult fish were moved to the alternate flow regime and allowed to acclimate for eighteen weeks. We then measured the effects of starting environment, transfer between environments, and final environment across several immune parameters. Fish population and treatment both significantly affected immune function. Stickleback from a population previously found to display the highest heritable levels of innate immunity displayed the highest oxidative burst capacity (ROS) regardless of tank environment. However, all fish in intermittent flow tanks (both resident and transfers) tended to have higher ROS production, more granulocytes, and greater spleen mass than in continuous flow. Variation in liver mass was mainly driven by population effects. We also provide limited data suggesting that the two water flow regimes harbor different microbial environments, offering a potential future direction for understanding the proximate connection between tank environment and immune variation. Overall, this work demonstrates that a simple change in water flow dynamics can induce immune flexibility. Perhaps more importantly, it also highlights the need for further research examining how naturally evolved genetic differences and environmental factors individually and jointly influence the magnitude and direction of immune responses.

evolutionary biology↗

bioRxiv2025

Egg hatching in the cestode Schistocephalus solidus shows no evidence of quorum sensing

Schistocephalus solidus is a parasitic cestode with a complex, multi-host life cycle. S. solidus reproduces in its terminal host either by exchanging gametes with similarly sized individuals or selfing. Fertilized eggs then pass through the feces of the host and hatch at the bottom of freshwater lakes. Previous work found that selfing greatly depresses egg hatching rates, presumably as a result of inbreeding depression. We predicted that S. solidus may have evolved quorum sensing (QS) during hatching as a mechanism to facilitate synchronized infection, thereby increasing the opportunity for outcrossing in its terminal host. We tested whether density-dependent hatch rates were present across three parasite populations, examining both outcrossed and selfed progeny. We predicted that if QS was present, it would be common across all populations, and that increasing egg density would result in higher hatching rates. We also expected that outcrossed eggs would hatch at higher rates than those produced via selfing. While we found different hatching rates between populations, there was no effect of egg density. Selfed eggs did hatch at significantly lower rates than outcrossed eggs, replicating previous findings. Although we failed to find density dependent hatching in our limited sample, we conclude by discussing the conditions in which QS may evolve in isolated S. solidus populations.

evolutionary biology↗

bioRxiv2025

Variable performance of widely used bisulfite sequencing methods and read mapping software for DNA methylation

DNA methylation (DNAm) is the most commonly studied marker in ecological epigenetics, yet the performance of library preparation strategies and bioinformatic tools are seldom assessed in genetically variable natural populations. We profiled DNAm in threespine stickleback (Gasterosteus aculeatus) liver tissue, using reduced representation bisulfite sequencing (RRBS) and whole genome bisulfite sequencing (WGBS) across technical and biological replicates. We additionally collated publicly available RRBS and WGBS data from taxonomically diverse organisms, and then compared how the most commonly used methylation software (Bismark) performed relative to alternative pipelines (BWA meth, BiSulfite Bolt, and Biscuit). Even after choosing parameters to maximize Bismarks mapping efficiency, it was still outperformed by all other methods. Surprisingly, newer tools overrepresented DNAm compared to older methods, highlighting the importance of testing methods on nonmodel organisms. There were also distinct differences in DNAm profiles produced across library preparation methods, with large impacts of population and read depth filters. Methylated sites unique to WGBS predominantly mapped to introns and intergenic regions, while sites unique to RRBS primarily overlapped with promoters and exons. Moreover, the prevalence of nucleotides with intermediate methylation (within individuals) was greatly reduced in RRBS. Together, this suggests that RRBS may be more useful for detecting functionally-relevant methylation differences. Based on these results, we provide methodological recommendations for improving the reliability and utility of DNAm profiles, particularly concerning the detection of functionally relevant DNAm differences in genetically diverse natural populations.

bioinformatics↗

bioRxiv2025

Hi-reComb: constructing recombination maps from bulk gamete Hi-C sequencing

Recombination is central to genetics and to evolution of sexually reproducing organisms. However, obtaining accurate estimates of recombination rates, and of how they vary along chromosomes, continues to be challenging. To advance our ability to estimate recombination rates, we present Hi-reComb, a new method and software for estimation of recombination maps from bulk gamete chromosome conformation capture sequencing (Hi-C). Simulations show that Hi-reComb produces robust, accurate recombination landscapes. With empirical data from sperm of five fish species we show the advantages of this approach, including joint assessment of recombination maps and large structural variants, map comparisons using bootstrap, and workflows with trio phasing vs. Hi-C phasing. With off-the-shelf library construction and a straightforward rapid workflow, our approach will facilitate routine recombination landscape estimation for a broad range of studies and model organisms in genetics and evolutionary biology. Hi-reComb is open-source and freely available at https://github.com/millanek/Hi-reComb.

genetics↗

bioRxiv2025

Needle in a haystack: A droplet digital polymerase chain reaction assay to detect rare helminth parasites infecting natural host populations

Helminths infect humans, livestock, and wildlife, yet remain understudied despite their significant impact on public health and agriculture. Because many of the most prevalent helminth-borne diseases are zoonotic, the health of diverse host species are closely interconnected. Therefore, understanding helminth transmission among wildlife could improve predictions and management of infection risks across species. A key challenge to understanding helminth transmission dynamics in wildlife is accurately and quantitatively tracking infection levels across hosts and environments. Traditional methods, such as visual parasite identification from environmental samples or infected hosts, are time-consuming, while standard molecular techniques (e.g., PCR and qPCR) often lack the sensitivity to reliably detect lower parasit burdens. These limitations often underestimate the prevalence and severity of infection, hindering efforts to manage infectious diseases. Here, we developed a multiplexed droplet digital PCR (ddPCR) assay to quantify helminth levels in aquatic habitats using 18S rRNA target genes. Using Schistocephalus solidus and their copepod hosts as a case study, we demonstrate ddPCRs sensitivity and precision. By establishing a 1:1 infection standard in the lab, we contextualize ddPCR gene concentration data to quantify both host and parasite numbers in field samples. The assay is highly reproducible, reliably detecting target genes at concentrations as low as 1 picogram of DNA in lab standards and field samples (multi-species and eDNA). Thus, we provide a toolkit for quantifying infection loads in intermediate hosts and monitoring infection dynamics across spatio-temporal scales in multiple helminth systems of concern for public health, agriculture, and conservation biology. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=139 SRC="FIGDIR/small/634533v1_ufig1.gif" ALT="Figure 1"> View larger version (66K): org.highwire.dtl.DTLVardef@1bc2e40org.highwire.dtl.DTLVardef@180822eorg.highwire.dtl.DTLVardef@1e2c2c8org.highwire.dtl.DTLVardef@621909_HPS_FORMAT_FIGEXP M_FIG Applications of ddPCR probe-primer design to parallel systems. Cyclopoid copepods serve as initial hosts for diverse helminthic diseases distributed globally. The primers designed in this assay are suitable for other systems, with minimal work required for probe design specific to each helminth species. C_FIG

molecular biology↗

bioRxiv2024

Destabilized host-parasite dynamics in newly founded populations

When species disperse into previously unoccupied habitats, new populations encounter unfamiliar species interactions such as altered parasite loads. Theory predicts that newly founded populations should exhibit destabilized eco-evolutionary fluctuations in infection rates and immune traits. However, to understand founder effects biologists typically rely on retrospective studies of range expansions, missing early-generation infection dynamics. To remedy this, we experimentally founded whole-lake populations of threespine stickleback. Infection rates were temporally stable in native source lakes. In contrast, newly founded populations exhibit destabilized host-parasite dynamics: high starting infection rates led to increases in a heritable immune trait (peritoneal fibrosis), suppressing infection rates. The resulting temporal auto-correlation between infection and immunity suggest that newly founded populations can exhibit rapid host-parasite eco-evolutionary dynamics.

evolutionary biology↗

bioRxiv2024

A spectral framework to map QTLs affecting joint differential networks of gene co-expression

Studying the mechanisms underlying the genotype-phenotype association is crucial in genetics. Gene expression studies have deepened our understanding of the genotype [->] expression [->] phenotype mechanisms. However, traditional expression quantitative trait loci (eQTL) methods often overlook the critical role of gene co-expression networks in translating genotype into phenotype. This gap highlights the need for more powerful statistical methods to analyze genotype [->] network [->] phenotype mechanism. Here, we develop a network-based method, called snQTL, to map quantitative trait loci affecting gene co-expression networks. Our approach tests the association between genotypes and joint differential networks of gene co-expression via a tensor-based spectral statistics, thereby overcoming the ubiquitous multiple testing challenges in existing methods. We demonstrate the effectiveness of snQTL in the analysis of three-spined stickleback (Gasterosteus aculeatus) data. Compared to conventional methods, our method snQTL uncovers chromosomal regions affecting gene co-expression networks, including one strong candidate gene that would have been missed by traditional eQTL analyses. Our framework suggests the limitation of current approaches and offers a powerful network-based tool for functional loci discoveries. Significance statementThis work addresses a key gap in understanding the mechanistic foundations for genotype-phenotype associations. While existing expression quantitative trait loci (eQTL) methods identify candidate loci affecting gene expression variants, they often neglect the crucial role of gene co-expression networks. Here, we develop a network-based QTL framework to map genetic loci affecting the gene co-expression network. Utilizing a tensor-based spectral approach, our snQTL method estimates the differential co-expression patterns and effectively identifies the associated genetic loci. Application of snQTL to three-spined sticklebacks revealed candidate loci missed by standard methods. This work suggests the limitations of current approaches and highlights the potential of network-based functional loci discovery.

genetics↗

bioRxiv2023

Evolution of horn length and lifting strength in the Japanese rhinoceros beetle Trypoxylus dichotomus

Rhinoceros beetle (Trypoxylus dichotomus) males have pitchfork-shaped head horns, which they use to pry rival males from the trunks of trees. In the largest males these horns can be three times the length of horns in the two closest sister species. Because this weapon functions as a lever, longer horns should lift with less force than shorter horns (the paradox of the weakening combatant) unless other elements of the weapon system (e.g., input lever length, muscle mass) evolve to compensate. We used next-generation sequencing approaches to consolidate 23 sample locations into 8 genetically distinguishable populations, reconstructing their historical relationships and providing a comprehensive picture of the evolution of this horn lever system. We show that head horns likely increased in length independently in the Northern and Southern lineages. In both instances this resulted in weaker lifting forces, but this mechanical disadvantage was later ameliorated, to some extent and in some locations, by subsequent reductions to horn length, changes in muscle size, or by an increase in input lever length (head height). Our results reveal an exciting geographic mosaic of differences in weapon size, weapon force, and in the extent and nature of mechanical compensation. Reconstructing the evolution of this weapon system offers critical insights towards meaningfully linking mating system dynamics, selection patterns, and diversity in sexually selected traits.

evolutionary biology↗

bioRxiv2022

Population genomics of a threespine stickleback tapeworm in Vancouver Island

We surveyed the genetic structuring of 12 Schistocephalus solidus tapeworm populations from Vancouver Island (BC, Canada) using ddRAD sequencing and compared it to that of their threespine stickleback fish hosts. There were small but mostly significant genetic differences among the tapeworm populations. PCA results separated the populations by watershed (from the lakes where the tapeworms were collected), but we could not determine if the genetic structures seen were due to discrete models (i.e. watershed) or to a continuous model (i.e. isolation by distance). However, the tapeworm genetic differences were significantly smaller (P < 0.001) than those of the fish, which indicates that the parasite disperses more readily than their fish hosts.

evolutionary biology↗

bioRxiv2022

Evidence of divergent selection in a parasite due to its host immunological respond

We investigated if an immunological response (i.e. fibrosis) in threespine stickleback fish can cause divergent selection in its tapeworm Schistocephalus solidus. We pooled tapeworms from six populations in Vancouver Island (BC, Canada) and sequenced the whole genome of these pools. Then we used a modified Population Branch Statistics (PBS) technique based on FST comparisons to find loci under divergent selection due to fibrosis. We found at least eight loci under divergent selection in tapeworm populations caused by this strong immunological respond to infection from the fish.

evolutionary biology↗

bioRxiv2021

Evolution of a costly immunity to cestode parasites is a pyrrhic victory

Parasites impose fitness costs on their hosts. Biologists therefore tend to assume that natural selection favors infection-resistant hosts. Yet, when the immune response itself is costly, theory suggests selection may instead favor loss of resistance. Immune costs are rarely documented in nature, and there are few examples of adaptive loss of resistance. Here, we show that when marine threespine stickleback colonized freshwater lakes they gained resistance to the freshwater-associated tapeworm, Schistocephalus solidus. Extensive peritoneal fibrosis and inflammation contribute to suppression of cestode growth and viability, but also impose a substantial cost of reduced fecundity. Combining genetic mapping and population genomics, we find that the immune differences between tolerant and resistant populations arise from opposing selection in both populations acting, respectively, to reduce and increase resistance consistent with divergent optimization. One Sentence SummaryRecently-evolved freshwater populations of stickleback frequently evolve increased resistance to tapeworms, involving extensive fibrosis that suppresses parasite growth; because this fibrosis greatly reduces fish fecundity, in some freshwater populations selection has favored an infection-tolerant strategy with fibrosis suppression.

evolutionary biology↗

bioRxiv2020

Immune gene expression covaries with gut microbiome composition in stickleback

Commensal microbial communities have immense effects on their vertebrate hosts, contributing to a number of physiological functions as well as host fitness. In particular, host immunity is strongly linked to microbiota composition through poorly understood bi-directional links. Gene expression may be a potential mediator of these links between microbial communities and host function. However few studies have investigated connections between microbiota composition and expression of host immune genes in complex systems. Here we leverage a large study of laboratory-raised fish from the species Gasterosteus aculeatus (three-spined stickleback) to document correlations between gene expression and microbiome composition. First, we examined correlations between microbiome alpha diversity and gene expression. Our results demonstrate robust positive associations between microbial alpha diversity and expression of host immunity. Next, we examined correlations between host gene expression and abundance of microbial taxa. We identified 15 microbial families that were highly correlated to host gene expression. These families were all tightly correlated to host expression of immune genes and processes, falling into one of three categories: those positively correlated, negatively correlated, and neutrally related to immune processes. Furthermore, we highlight several important immune processes that are commonly associated with abundance of these taxons, including both macrophage and B cell functions. Further functional characterization of microbial taxa will help disentangle the mechanisms of the correlations described here. In sum, our study supports prevailing hypotheses of intimate links between host immunity and gut microbiome composition.

immunology↗

bioRxiv2020

A test of the Baldwin Effect: Differences in both constitutive expression and inducible responses to parasites underlie variation in host response to a parasite

Despite the significant effect of host-parasite interactions on both ecological systems and organism health, there is still limited understanding of the mechanisms driving evolution of host resistance to parasites. One model of rapid evolution, the Baldwin Effect, describes the role of plasticity in adaptation to novel conditions, and subsequent canalization of associated traits. While mostly applied in the context of environmental conditions, this theory may be relevant to the evolution of host resistance to novel parasites. Here we test the applicability of the Baldwin Effect to the evolution of resistance in a natural system using threespine stickleback fish (Gasterosteus aculeatus) and their cestode parasite Schistochephalus solidus. We leverage a large transcriptomic data set to describe the response to S. solidus infection by three different genetic crosses of stickleback, from a resistant and a tolerant population. Hosts mount a multigenic response to the parasite that is similar among host genotypes. In addition, we document extensive constitutive variation in gene expression among host genotypes. However, although many genes are both infection-induced and differentially expressed between genotypes, this overlap is not more extensive than expected by chance. We also see little evidence of canalization of infection-induced gene expression in the derived resistant population. These patterns do not support the Baldwin Effect, though they illustrate the importance of variation in both constitutive expression and induced responses to parasites. Finally, our results improve understanding of the cellular mechanisms underlying a putative resistance phenotype (fibrosis). Combined, our results highlight the importance of both constitutive and inducible variation in the evolution of resistance to parasites, and identify new target genes contributing to fibrosis. These findings advance understanding of host-parasite interactions and co-evolutionary relationships in natural systems.

immunology↗

bioRxiv2020

Split-HaloTag Imaging Assay for in vivo 3D-Microscopy and Subdiffractional Analyses of Protein-Protein Interactions

An ever-increasing number of intracellular multi-protein networks have been identified in plant cells. Split-GFP based protein-protein interaction assays combine the advantages of in vivo interaction studies in a native environment with additional visualisation of protein complex localisation. Due to its simple protocols, it has become one of the most frequently used methods. However, standard fluorescent proteins entail several drawbacks for sophisticated microscopy. With the HaloTag(R) system, these drawbacks can be overcome as this reporter forms covalent irreversible bonds with synthetic photostable fluorescent ligands. Dyes can be used in adjustable concentrations and are suitable for advanced microscopy methods. Therefore, we established the Split-HaloTag(R) imaging assay in plants which is based on the reconstitution of a functional HaloTag(R) protein upon protein-protein interaction and subsequent covalent binding of an added fluorescent ligand. Its suitability and robustness were demonstrated using well-characterised interactions as an example for protein-protein interaction at cellular structures: the molybdenum cofactor biosynthesis complex anchoring to filamentous actin. Additionally, a specific interaction was visualised with subdiffractional polarisation microscopy in a more distinctive manner as example for sophisticated imaging. Split-GFP and Split-HaloTag(R) can complement one another as Split-HaloTag(R) represents an alternative option and an addition to the large toolbox of in vivo methods. Therefore, this promising new Split-HaloTag(R) imaging assay provides a unique and sensitive approach for more detailed characterization of protein-protein interaction with specific microscopic techniques such as 3D-imaging, single molecule tracking and super-resolution microscopy.

plant biology↗