Molecular Ecology

Vole and lemming population cycles are an enigma in ecology. Decades of field observations and experimental manipulations have revealed that cycles cannot always be explained by extrinsic factors in the environment, including food availability or predator numbers. Thus, it has been proposed that intrinsic mechanisms, such as adaptive alterations in phenotype during different phases of the cycle, drive population dynamics. However, the mechanisms underlying such phenotypic changes have not been elucidated. We test the hypothesis that epigenetic changes occur over population cycles by comparing whole epigenome DNA methylation changes in brain tissue collected from northern red-backed voles (Clethrionomys rutilus) in a wild, naturally cycling population during the peak, decline, and low years. Overall, the greatest number of differentially methylated CG sites (DMCs) and differentially methylated regions (DMRs) were detected in comparisons between voles from the peak phase and low phase of the cycle. We highlight methylation differences in the promoter region of ATP synthase subunit c (Atp5g3) and an intron of insulin-like growth factor 1 receptor (Igf1R), which may be associated with growth, development, and bioenergetics. There were additional changes in the promoters of members of the cytochrome P450 enzyme family, including Cyp1a1, associated with estrogen metabolism, as well as the promoter of macrophage migration inhibitory factor (Mif), and in an exon of serum/glucocorticoid regulated kinase (Sgk1), which may link changes in stressors to direct brain changes. Our study is the first interrogation into broad epigenetic changes associated with natural population cycle phase in a wild mammal.

Understanding the drivers of genomic health and their consequences for population viability is often overlooked but potentially important to effective conservation amidst the biodiversity crisis of the Anthropocene. Leatherback turtle (Dermochelys coriacea) populations have declined globally due to anthropogenic factors, with some populations losing over 90% of their abundance over the past 30-50 years. While conservation efforts have been successful in stabilizing some populations, others continue to decline, and the reasons for these differential trajectories remain unclear. To assess how recent demographic factors, such as population size and decline, influence population genomic health, we combined population monitoring information with medium depth whole-genome and reduced representation resequencing data from globally representative populations. We found that small-stable populations have lower genomic diversity and higher inbreeding than large declining populations, reflecting prolonged small population sizes and limited gene flow. Yet, small-stable populations also show evidence of deleterious allele purging, suggesting genetic resilience. This, combined with lack of detectable genomic erosion over the study period, provides hope for potential recovery of healthy leatherback populations provided that anthropogenic threats are effectively mitigated. However, potential time lags and possible recent increases in inbreeding among close relatives in recently declined populations warrant continued monitoring and assessment. Genomic and abundance-based metrics were less aligned following rapid population declines, emphasizing the different timescales of the evolutionary and demographic processes they reflect, respectively, and the strength in their complementary, integrative use for extinction risk assessments. This also supports that it is not too late to turn the tide for recently declined leatherback populations and that continued investment in conservation efforts and threat reductions are warranted. Collectively, our results highlight how recent and historical demography shapes current genomic health and recovery potential in leatherback turtles, aids understanding of current risks and informs future conservation and management strategies.

Genomic forecasting approaches based on genotype-environment associations (GEAs) are increasingly used to estimate genomic offsets (GOs), which predict population maladaptation and extinction risk under current or future climatic conditions. Despite their widespread use, only a subset of studies have evaluated how accurately GOs predict (mal)adaptation, limiting their interpretation and application in policy and management. Here, we used GEA analyses to estimate GOs for past, present, and future climates in Lycaeides butterflies, focusing on the causes of variation in GOs among populations and their relationships with demographic parameters inferred from population genomic data. Using multivariate linear regression and genotyping-by-sequencing data from 42 Lycaeides populations (922 butterflies), we found that mean annual temperature, cumulative annual precipitation, and hybridization history together explained 47.6% of variation in genome-wide allele frequencies. Genomic offsets differed substantially among populations and across past, present, and future climates, with evidence for increasing maladaptation under more distant future climate scenarios. We found no relationship between GOs for present climates and contemporary effective population size. In contrast, genetic diversity, which reflects long-term effective population size, and local rates of gene flow together explained 27.3% of variation in contemporary GOs. Populations with higher genetic diversity and more gene flow exhibited lower GOs, consistent with the hypothesis that genetic diversity enhances adaptive capacity and that gene flow may introduce adaptive alleles. Overall, our results support the utility of GO predictions, particularly when validated with independent measures of adaptation, while cautioning against simplistic interpretations of GO as a direct measure of maladaptation in conservation and management contexts.

Birdsong mediates territory acquisition and mate choice. In agonistic interactions, local songs generally elicit stronger responses than songs from more distant populations. However, the molecular mechanisms associated with differential responses to local vs. foreign songs are poorly understood. We addressed this knowledge gap by combining behavioral assays in the field with blood transcriptomic analysis, using a within-subjects design to ask whether male song sparrows (Melospiza melodia) show differential gene expression when exposed to playback of local and foreign songs. Transcriptomic profiles reflected the difference in behavioral response to local vs. foreign songs, with individuals exposed to local songs showing greater expression of genes associated with song perception and production, anti-inflammatory responses and energy metabolism. Our study suggests that changes in expression of key molecular pathways correlate with behavioral responses to geographic song variation, providing insight into the potential mechanisms regulating signal recognition and response to social challenges. HighlightsO_LIGene expression in sparrow blood was measured after simulated territorial intrusion. C_LIO_LIStronger response to local songs was associated with differential gene expression. C_LIO_LISong-associated genes (FOXP2, NRXN1) had higher expression when birds heard local songs. C_LIO_LIGene expression in the blood contains potential biomarkers of song recognition. C_LI

Strong population contractions can leave a persistent genomic legacy that can influence populations long after their demographic recovery. While bottlenecks facilitate the removal of strongly deleterious mutations, the effectiveness of purging may be limited in historically small populations. The Kirtlands warbler (Setophaga kirtlandii) is a rare North American songbird with an ancestrally small population. After narrowly evading extinction, they are one of few species that have been delisted from federal protections in the USA. Despite their recovery, a previous study showed evidence for recent inbreeding and a high burden of deleterious mutations that may have not been purged despite strong bottlenecks. Historical DNA offers a unique opportunity to understand the consequences of recent demographic declines on genetic diversity. Here, we use DNA from over 100-year-old museum specimens to estimate changes in genetic load in the Kirtlands warblers pre- and post-bottleneck. We validate our results with forward-in-time genetic simulations and explore how sample size and missing data can affect estimates. Both empirical data and simulations suggest a reduced ability to purge deleterious mutations in this historically small population. Our simulations also highlight that limited sampling design and data quality can constrain the ability to detect changes.

Hybridisation between wild and domestic taxa can favour the spread of domestic alleles into wild populations through backcrossing. The complex interplay of random genetic drift, recombination, and selection can shape the fate of introgressed alleles. Maladaptive domestic variants are likely to be purged by natural selection, but others may persist across generations. It has long been known that the Apennine Italian wolf population, exposed to large numbers of free-ranging dogs, has experienced extensive introgression. The unusually high frequency of black wolves observed in Italy, compared to other European populations, may parallel patterns documented in North American wolves, where the melanistic KB allele at the CBD103 gene, of domestic origin, has spread over thousands of years of introgression. We tested whether the KB mutation entered the peninsular Italian wolf population via hybridisation and spread through adaptive introgression. Genome-wide analyses of black and wild-type (grey-coated) Apennine wolves showed no clear signatures of recent dog ancestry in most melanistic animals. Our ancestry reconstruction approaches identified two distinct KB haplogroups of domestic origin, suggesting multiple introgression events. Notably, we found molecular evidence consistent with balancing selection on the KB haplotypes, whose functional role, nonetheless, warrants further research. Therefore, the microevolutionary genomic and ecological consequences of wolf-dog hybridisation in Italy should be carefully investigated to inform appropriate science-based conservation management strategies.

Allopatric isolation under contrasting environments can drive rapid phenotypic divergence, even over contemporary timescales. Rapid changes in morphology or physiology can allow organisms to adapt to biotic and abiotic characteristics of their habitats. While studying metabolism, growth and resources needs may allow to understand adaptation to several selective pressures, these traits are rarely jointly considered. We investigated morphological, growth, and metabolic divergence in two allopatric populations of Arctic charr (Salvelinus alpinus) sharing a common evolutionary origin but inhabiting contrasting environments. We combined field observations, common garden and quantitative genetic approaches to disentangle contributions of genetic divergence and plasticity to phenotypic variability. Wild adults differed in body shape and growth trajectories, potentially reflecting plasticity related to resource availability and temperature variations. Under common garden conditions, juveniles displayed inter-population differences in routine metabolic rate, its allometric scaling with body mass. These patterns suggest divergent selection on physiological traits. Despite low neutral genetic differentiation, phenotypic divergence unfolded in fewer than 100 years, suggesting that plasticity and selection can promote rapid multi-trait changes. These findings highlight that considering changes in physiological, growth and morphological traits can reveal the adaptive potential of small, isolated populations facing rapid environmental change.

Sex ratio distorters (SRDs) are heritable elements that bias offspring sex ratios to enhance their transmission. In the terrestrial isopod Armadillidium vulgare, feminization of genetic males can occur through vertical transmission of the sex ratio distorter known as the f-element, as well as through infection by Wolbachia, a maternally inherited bacterial endosymbiont that can alter host reproduction. Previous studies have focused on the distribution of SRDs and their associations with mitochondrial haplotypes in native European populations, but these patterns are poorly understood in the United States. In this study, we sampled A. vulgare in 12 states, screening individuals for Wolbachia infection, the presence of the f-element, and mitochondrial haplotypes. We found that Wolbachia shows a heterogeneous distribution across populations and haplotypes, in contrast with stronger associations in Europe. The f-element occurred in lower overall frequencies but showed a strong association with mitochondrial haplotype VI. These results indicate that patterns associated with SRD differ from those observed in Europe and suggest that multiple introductions and population mixing have shaped these distributions.

Sexual selection arises from individual differences in reproductive success, which can drive the maintenance of genetic polymorphisms in genes subject to balancing selection by the pleiotropic effects that trade-off between survival and reproduction. However, the extent to which sexual selection maintains genetic polymorphisms in wild populations remains unclear. Here, we explored on genomic signatures of balancing selection and selective sweep in the northern medaka, Oryzias sakaizumii in Japan by performing whole-genome resequencing of wild individuals. In addition, we re-evaluated the population genetic structure and admixture of Oryzias latipes and O. sakaizumii across the Japanese archipelago and detected genomic regions affected by introgression. Regions with signatures of selection from multiple statistics were located on eleven chromosomes. In particular, a region spanning 4.25 to 6.80 Mb on chromosome 18 showed high genetic diversity that could not be explained by sex differentiation or introgression from O. latipes in Eastern Japan. This pattern suggests that balancing selection maintains genetic polymorphisms in O. sakaizumii. Specifically, because a previously reported quantitative trait locus associated with female mating behavior overlaps with this region, we infer that sexual selection contributes to the maintenance of genetic polymorphism at this locus.

Sex ratio is a key demographic parameter shaping population dynamics and evolutionary trajectories. In biocontrol agents, demographic bottlenecks during species introduction to a new habitat and subsequent mass rearing can elevate inbreeding, potentially biasing sex ratios through sex-specific mortality associated with inbreeding depression. Moreover, reproductive endosymbionts such as Wolbachia are known to manipulate host reproduction and further skew sex ratios. However, the relative contributions of these processes to sex-ratio variation remain poorly resolved. In this study, we evaluated the effects of cross-generational full-sibling inbreeding and Wolbachia infection on sex ratio and key life-history traits in the biocontrol beetle Zygogramma bicolorata using controlled laboratory crosses across three generations. Inbreeding did not significantly alter offspring sex ratio, which remained close to parity across generations, while pupal mortality increased in later generations, consistent with delayed expression of inbreeding depression. Adult body weight remained largely unaffected by inbreeding. Wolbachia infection was detected in a subset of females and was associated with a modest but significant increase in female-biased offspring production, although the effect was variable across lineages. Strain typing identified a single supergroup A Wolbachia, consistent with previous descriptions of the wBic strain from this species. These findings indicate that sex-ratio variation in introduced populations of Z. bicolorata is not driven by inbreeding alone but instead emerges from the interaction between demographic processes and symbiont-mediated effects, providing crucial insights for optimizing biocontrol programs where sex-ratio stability is essential for population establishment and persistence. SignificanceSex ratio is a key determinant of population growth and stability - the essential parameters determining success of biocontrol programs. Yet, the mechanisms shaping sex-ratio variation remain poorly resolved. Using controlled crosses in Zygogramma bicolorata, we show that short-term inbreeding does not directly alter sex allocation, despite inducing delayed fitness costs through increased pupal mortality. In contrast, Wolbachia infection contributes to female-biased offspring production, although with variable outcome across lineages. These findings demonstrate that sex-ratio variation in Z. bicolorata arises from the interaction of demographic processes and symbiont effects, rather than a single mechanism, with important implications for predicting the establishment, persistence, and efficacy of mass-reared biocontrol populations.

The fitness of immigrants and their descendants determines the effectiveness of gene flow. Genetic incompatibilities or outbreeding depression can limit the spread of novel alleles, while highly fit immigrant lineages can hasten introgression. These fitness effects of gene flow can also differ between generations as immigrant and resident haplotypes recombine. Understanding the genetic factors that shape immigrant fitness over multiple generations is increasingly important as habitat fragmentation threatens populations by reducing genetic variation and leading to increased levels of inbreeding. Few studies have measured the multigenerational fitness of immigrant lineages, especially within populations that had histories of high gene flow. We used 33 years of life history and pedigree data on a population of Florida scrub-jays (Aphelocoma coerulescens) with historically high immigration to quantify the fitness of immigrants and their descendants. We compared the fitness of immigrants and residents as well as their resulting descendants (F1, F2, etc.) to determine the composite genetic effects responsible for fitness differences. We found evidence of additive benefits of immigrant ancestry and heterosis driven by non-additive effects that persists for multiple generations. These results are promising for conservation efforts aiming to increase connectivity and illustrate the complex dynamics that determine the rates of introgression in natural populations.

Accelerated warming at high elevations is having a disproportionate impact on alpine species. While assessments of climate vulnerability require quantifying the ecological and evolutionary components of adaptive capacity, such assessments are rare, especially in alpine systems. We leverage recent advances in population and landscape genomics to assess how variation in spatial heterogeneity and population connectivity across alpine systems influences adaptive capacity, using the North American Rosy-Finch species complex as a model system. In doing so, we clarify taxonomic relationships across the complex and identify one new ESU, the Sierra Nevada Rosy-Finch, based on its combined ecological and evolutionary distinctiveness. We then illustrate how combining genomic analyses with ecological data can improve estimates of adaptive capacity, sensitivity, and exposure and ultimately clarify climate vulnerability. Overall, our integrative analyses revealed that more isolated lineages, such as the Sierra Nevada Rosy-Finch, have lower adaptive capacity and face disproportionately high risks from climate change. This work highlights how conservation strategies that account for the multidimensional aspects of adaptive capacity can improve estimates of climate vulnerability.

Antimicrobial resistance (AMR) genes are increasingly recognized as an emerging environmental contaminant. Yet, the ecological mechanisms shaping their distribution across natural landscapes remain poorly understood. Here, we quantified AMR gene abundances in microbial communities sampled from wild fish from eight freshwater lakes on Vancouver Island and paired these gene-level measurements with fine-scale limnological and land-use data. Using droplet digital PCR, field surveys, and an iterative spatial forecasting framework that integrates Random Forest models with regression kriging, we explored how watershed-scale processes relate to variation in AMR genes across lakes. Our analyses reveal potential associations between elevated AMR gene levels, changes in water quality, deforestation, and geographic proximity to salmon aquaculture. By integrating data across biological and spatial scales, from genes within microbial communities to lake-level conditions and landscape patterns, this study illustrates the value of combining quantitative molecular measurements with geospatial modeling to identify environmental factors that may promote antimicrobial resistance in natural systems. Our approach provides a proof-of-concept and a general predictive framework for generating hypotheses and informing future monitoring efforts aimed at understanding, managing, and forecasting environmental reservoirs of resistance. SignificanceAntimicrobial resistance (AMR) genes are ancient components of environmental microbiomes. Yet, the mechanisms that generate modern hotspots of resistance across natural landscapes remain unclear. Here, we reveal how watershed-scale environmental change, including water quality metrics linked with deforestation and proximity to salmon aquaculture, predicts elevated AMR gene levels in the microbiomes of wild fish populations. By combining quantitative droplet digital PCR with ecological data and geospatial modeling, we move beyond isolated surveillance data to identify ecological mechanisms that promote antimicrobial resistance in freshwater ecosystems. This integrative approach provides mechanistic insight into why certain habitats, and the organisms within them, become reservoirs of resistance while others do not. Our findings highlight the importance of ecological context in understanding resistance evolution and offer a predictive tool for informing proactive monitoring and management strategies.

Background and AimsGroundwater-dependent ecosystems support disproportionate biodiversity in arid regions, yet the population genetics of spring-specialist plants remains poorly understood. Here, we present the first species-wide genetic dataset for crimson monkeyflower ( Mimulus verbenaceus, Phrymaceae), a spring-specialist plant distributed in seeps, springs, and associated riparian areas across desert regions of North America. MethodsUsing genome-wide reduced representation sequencing data consisting of 10,760 SNPs from 175 individuals across 17 populations, we characterized the patterns of genetic diversity using FST and Neis D. Population structure was assessed using ADMIXTURE and PCA. We examined the contributions of climate to range-wide genetic variation in crimson monkeyflower using redundancy analysis. Key ResultsPatterns of genetic differentiation were more consistent with those of spring-specialist animal taxa than those of upland plants or generalist riparian plants. We found strong population structure at both broad regional scales and at fine local scales. While riparian connectivity influenced local patterns of diversity, adaptation to local climatic variation was more influential at regional scales, with temperature, relative humidity, and a monsoon-driven climate gradient structuring genetic differentiation. ConclusionsOur findings highlight the distinctive influence of isolated perennial groundwater sources, as well as adaptation to climate, in shaping genetic variation in this spring-specialist plant. These findings suggest that spring-specialist plants deserve special consideration in ecological theory, management, and conservation.

The field of genetics of bird migration advances, driven by exponential refinements of sequencing and tracking technologies. In willow warblers (Phylloscopus trochilus), a complex repeat-rich region named MARB (Migration Associated Repeat Block) has recently been found to correlate with the routes taken by individual birds from Europe to their African wintering grounds. However, the genomic location of this region remains unknown. Here, we characterized MARB using a combination of approaches to understand how it evolved. We describe the region using long-read genome assemblies of two willow warbler subspecies (P. t. trochilus and P. t. acredula), two related species, the common chiffchaff (P. collybita) and the greenish warbler (P. trochiloides), and whole genome sequencing data from 76 willow warblers. Finally, we applied karyotyping and fluorescent in situ hybridization techniques on willow warbler spermatocytes to cytogenetically locate MARB. Due to the many repeats, we cannot order scaffolds in silico, but probe hybridization on the karyotype shows that MARB constitutes a single locus (~27.5 Mb) spanning most of the 11th largest chromosome in the willow warbler genome. Interestingly, the MARB regions of all species share several characteristics such as relatively high GC content (50%), a high density of specific repeat families and notably, more than 800 olfactory receptor sequences. Regions homologous to MARB may exist in several migrant bird genomes, though currently unassembled due to their complexity. Resolving these in species with similar migratory polymorphisms to willow warblers will be essential to determine whether MARB influences migratory behaviour across species.

The evolutionary divergence between Henophidia (non-venomous) and Caenophidia (venomous) snakes has produced distinct cranial morphologies, digestive strategies, and presence of specialised venom systems in Caenophidia, yet the extent to which these long-standing diverging trajectories have shaped cloacal microbiota assembly remains poorly understood. We characterised cloacal microbiota in 70 captive snakes (52 Caenophidia, 18 Henophidia) by 16S rRNA amplicon sequencing. Beta diversity was tested by PERMANOVA, differential abundance by ANCOM-BC2, community types by Dirichlet Multinomial Mixture modelling (DMM), and microbial interactions by SparCC co-occurrence networks. Predicted functional potential (PICRUSt2) was analysed by ALDEx2 differential abundance testing and elastic net feature selection. Henophidia exhibited significantly higher bacterial richness and greater compositional variability than Caenophidia. Community composition showed clade-associated differences (PERMANOVA) and partitioned into two distinct DMM community types. The Henophidia network was 11.9-fold denser and more modular, with Burkholderiaceae as a keystone hub, whereas the Caenophidia network was sparse. Henophidia showed predicted enrichment in C1 metabolic pathways (ethylmalonyl-CoA, formaldehyde assimilation I, glycine betaine degradation I, methylaspartate cycle), aromatic compound catabolism, and nitrogen recycling, whilst Caenophidia showed enrichment in allantoin and glucuronate degradation. This multi-method analysis suggests Burkholderiaceae as a candidate keystone taxon in Henophidia and indicates that phylogenetic clade is a major contributor to cloacal microbiota structure. The lower richness in Caenophidia raises a testable hypothesis that broad-spectrum antimicrobial activity of their venom components may selectively filter susceptible microbial lineages, motivating future shotgun metagenomic studies in wild populations of snakes.

The deployment of clothianidin-based insecticide formulations in malaria vector control has highlighted the capacity of Anopheles funestus to displace more susceptible mosquito species in treated areas and to rapidly evolve resistance under selection pressure. Metabolic detoxification, together with structural and genetic changes in nicotinic acetylcholine receptors (nAChRs), the primary molecular targets of neonicotinoids, can reduce insecticide efficacy. Here, we characterized amino acid substitutions across all 11 nAChR subunits in An. funestus to assess standing variation that may facilitate adaptive responses to chemical exposure. Using whole-genome sequencing data from 656 mosquitoes sampled in 13 African countries, we found marked contrasts in the distribution of nonsynonymous variants among nAChR subunits. Most subunits are strongly constrained and carry no missense variants, whereas two loci (3 and 7) display three geographically widespread amino acid substitutions across the continent. In contrast, 9 and {beta}2 accumulate dozens of nonsynonymous mutations occurring at intermediate to high frequencies, including within domains involved in orthosteric ligand binding and channel gating. Genetic differentiation at nAChR loci among populations from different countries is low to moderate, although several nonsynonymous mutations display high FST values consistent with geographic structuring. These results highlight relaxed constraint on two subunits that may provide opportunities for evolutionary diversification within a conserved family of multimeric receptor assemblies. Such diversification has not been observed in vector species displaced by An. funestus in indoor residual spraying areas, and the potential implications for reduced sensitivity to neonicotinoids are discussed.

Oxygen limitation is a widespread environmental constraint that shapes physiological and evolutionary responses across ecosystems. A central unresolved question is whether tolerance to hypoxia reflects generalized stress responses or coordinated regulatory strategies shaped by long-term environmental exposure. Here, we use comparative transcriptomic analyses to examine gene expression responses to low oxygen in two aquifer-dwelling stoneflies (Isocapnia sp. and Paraperla frontalis) and one benthic species (Sweltsa sp.) under controlled conditions. Time-series analysis in Isocapnia sp. revealed a multi-phase transcriptional response involving early regulatory activation, metabolic reorganization, and late-stage cellular stabilization. Across aquifer taxa, hypoxia was associated with downregulation of energy-demanding processes and upregulation of pathways related to oxidative stress mitigation, metabolite transport, and protein folding, consistent with coordinated cellular adjustment to oxygen limitation. In contrast, the river benthic species exhibited transcriptional profiles dominated by neural signaling, ion channel activity, and structural remodeling, which are patterns consistent with acute physiological stress rather than coordinated regulation. Despite these differences, all taxa showed modulation of ion transport and calcium signaling pathways, suggesting conserved mechanisms of hypoxia sensing. Together, these results indicate that transcriptional responses to hypoxia differ systematically with habitat and are consistent with the evolution of distinct regulatory strategies in chronically hypoxic environments. Significant statementOxygen limitation is a common environmental challenge that affects organisms across aquatic and terrestrial ecosystems, yet the mechanisms by which species cope with low oxygen remain incompletely understood. A key question is whether tolerance to hypoxia reflects common stress responses or the evolution of coordinated metabolic regulatory strategies under chronic exposure. By comparing gene expression responses in closely related aquatic insects from oxygen-variable underground aquifers and oxygen-rich river habitats, we show that species that evolved under persistent hypoxia exhibit transcriptional patterns consistent with energy conservation and cellular stabilization, whereas those experiencing hypoxia as a transient stress display signature of physiological disruption. These findings highlight fundamental differences between evolutionarily adaptive and acute stress-driven responses to environmental change and provide insight into how organisms may respond to increasing hypoxia under global change.

Parasites are ubiquitous drivers of host evolution by exerting strong selective pressure on natural populations. Understanding the genetic basis of host susceptibility to infection is important to know how host-pathogen interactions shape patterns of resistance and diversity in natural populations. We conducted a genome-wide association study (GWAS) to identify host genetic variants associated with infection by helminth and blood pathogens in spatially structured populations of Bank voles (Myodes glareolus; (Schreber, 1780). We genotyped 182 individuals sampled from ten sites in central Europe using quaddRAD sequencing, retaining 30,206 high-quality single-nucleotide polymorphisms (SNPs). Associations between SNP genotypes and parasite infection status were tested using mixed models controlling for relatedness, with host body mass included as a covariate. Across parasite taxa, we identified twelve SNPs exceeding genome-wide significance with the strongest signals detected for the intestinal nematode Heligmosomum mixtum. The variants identified are all intergenic, intronic, upstream or downstream of genes, with none predicted to alter coding sequences. These genes are not classical immunity genes but some are implicated in cytokine production, PI3K/AKT signalling and p38 MAPK pathway, suggesting that selective pressure from pathogens does not only act on known immunity genes, but on broader regulatory and metabolic networks. This finding suggests that variation in gene expression may be important for the differences in host susceptibility or resistance to parasitic infections.

RDL (Resistance to dieldrin) is a GABA-gated chloride channel that was first described as target of the insecticide dieldrin. Despite dieldrin being discontinued for decades because of its environmental per-sistence and health concerns, Rdl resistance mutations (A296S, A296G) continue at high frequencies in natural populations of the malaria mosquito Anopheles gambiae complex across Africa, suggesting a selective advantage. We have recently shown that RDL acts as a critical modulator of mosquito auditory sensitivity. Because acoustic recognition is essential for mate acquisition in An. gambiae, we hypothesized that these mutations confer a pleiotropic effect on mating success in the field, mediated through altered acoustic sensitivity, with potential consequences for sexual selection. We first provide laboratory evidence that resistance mutations enhance auditory behaviours of An. gambiae and show that the effect of environmental noise on mating success depends on the male Rdl genotype. We then conduct field collections in the city of Bangui (Central African Republic) and surrounding rural areas, revealing the presence of Rdl resistant alleles and their association with the urban environment, and within the city, with the noisiest locations. We also show decreased mating success of susceptible females with increasing noise levels, suggesting detrimental effects. Together, our findings support that Rdl resistance mutations enhance auditory function and mating success in acoustically challenging environments. We propose that this auditory advantage may contribute, together with other selective pressures such as cross-selection by other insecticides, to the persistence of these alleles in nature and may facilitate urban colonization by malaria vectors. Our study reveals, for the first time, an unintended evolutionary consequence of insecticide use, where a resistance mutation has been co-opted to enhance sensory performance and ecological adaptation, with significant implications for vector management strategies.