Find research datasets worth reusing

Data from: Integrating population genetics to define conservation units from the core to the edge of Rhinolophus ferrumequinum western range

The greater horseshoe bat (Rhinolophus ferrumequinum) is among the most widespread bat species in Europe but it has experienced severe declines, especially in Northern Europe. This species is listed Near Threatened in the European IUCN Red List of Threatened Animals and it is considered to be highly sensitive to human activities and particularly to habitat fragmentation. Therefore, understanding the population boundaries and demographic history of populations of this species is of primary importance to assess relevant conservation strategies. In this study, we used 17 microsatellite markers to assess the genetic diversity, the genetic structure and the demographic history of R. ferrumequinum colonies in the western part of its distribution. We identified one large population showing high levels of genetic diversity and large population size. Lower estimates were found in England and northern France. Analyses of clustering and isolation by distance suggested that the Channel and the Mediterranean seas could impede R. ferrumequinum gene flow. These results provide important information to improve the delineation of R. ferrumequinum management units. We suggest that a large management unit corresponding to the population ranging from Spanish Basque country to northern France must be considered. Particular attention should be given to mating territories as they seem to play a key role in maintaining the high levels of genetic mixing between colonies. Smaller management units corresponding to English and northern France colonies must also be implemented. These insular or peripheral colonies could be at higher risk of extinction in a near future.

opencc-by-4.0Oct 2020View details →

zenodo36/100

Drivers of within-host genetic diversity in acute infections of viruses

Mutations frequencies of HIV, RSV and CMV samples taken from acute infections.

Under the radar: genetic assessment of Rio Grande Shiner (Notropis jemezanus) and Speckled Chub (Macrhybopsis aestivalis), two Rio Grande basin endemic cyprinids that have experienced recent range contractions

The Rio Grande drainage of the southwestern United States and Mexico has undergone intense anthropogenic alteration by water diversions, extraction and associated habitat changes. These alterations have disproportionately impacted the pelagic broadcast spawning guild of minnows (pelagophils). Several Rio Grande endemic pelagophils, including the co-occurring Rio Grande Shiner (Notropis jemezanus) and Speckled Chub (Macrhybopsis aestivalis), have experienced dramatic recent range-wide declines yet have slipped under the radar of conservation efforts. The status of N. jemezanus and M. aestivalis in the Rio Grande and Pecos River was evaluated and standing genetic variation were characterized. Genetic evidence indicates that populations of both species found in the Rio Grande and Pecos River are genetically distinct. Additionally, 159 outlier loci were identified in M. aestivalis suggesting possible local adaptation in the Rio Grande and Pecos River populations. Though range-wide genetic data are limited, N. jemezanus populations in both rivers harbor considerable genetic diversity. Mitochondrial data from both taxa are consistent with a history of secondary contact between formerly isolated populations with deeply divergent haplotypes found within the Rio Grande and Pecos River populations of N. jemezanus and within the Rio Grande population of M. aestivalis. Extensive survey efforts in the lower Rio Grande and its tributaries in Texas document significant range contraction and near extirpation of N. jemezanus from this part of the basin; highlighting the need for immediate action to protect the species.

Genetic structures across a biogeographical barrier reflect dispersal potential of four Southeast Asian mangrove plant species

Aim Biogeographic barriers restrict the movement of individuals, resulting in population divergence, genetic differentiation, endemism and speciation. Yet, some barriers demonstrate unequal effect across species depending on species dispersal, which manifests in varying genetic structure. We test the hypotheses that the genetic structure of four coastal mangrove species would reflect differences in dispersal potential across the Malay Peninsula, a major biogeographic barrier in the Indo-West Pacific region. Location Twelve sites from the east and west coasts of the Malay Peninsula. Taxon Mangrove trees Avicennia alba, Sonneratia alba, Bruguiera gymnorhiza, and Rhizhophora mucronata. Methods For each species, we characterized genetic structure and gene flow using seven to 12 species-specific nuclear microsatellite markers. We tested for east-west genetic differentiation across the peninsula, a stepping-stone migration pattern, and assessed the proportion of recent dispersal and direction of historical migration along the Malacca Strait. Results Significant east-west genetic differentiation across the peninsula was observed in A. alba, S. alba and B. gymnorhiza, and the effect was most pronounced for the two species with lower dispersal potential (A. alba, S. alba). In contrast, the two species with higher dispersal potential (B. gymnorhiza and R. mucronata) exhibited much higher proportion of recent inter-population migration along the Malacca Strait. The signature of historical colonization from refugia in the Andaman Sea (north-to-south migration along the Malacca Strait) predominated for A. alba and S. alba. Historical south-north migration predominated for R. mucronata and B. gymnorhiza. Main conclusions This study is the first to implicate dispersal potential as a causal factor of varying mangrove species genetic structure across a biogeographic barrier. The Malay Peninsula functions as a filter to gene flow rather than a barrier. The genetic structure in mangrove species with a higher dispersal potential is more congruent with contemporary gene flow while that of species with a lower dispersal potential reflects historical processes.Our findings hint at the role of dispersal potential as a predictor of gene flow in mangroves.

Scripts from: Controlling evolution in genetically engineered systems through repeated introduction

Genetically engineered transgenes evolve in the same way as other genetic material. However, evolution in engineered genes is often undesirable and can negatively affect their stability, frequency, and efficacy over time. Methods that maintain the stability of engineered genomes are therefore critical to the successful design and use of genetically engineered organisms. One potential method to limit unwanted evolution is by taking advantage of the ability of gene-flow to counter local adaption, a process of supplementation. Here we investigate the feasibility of supplementation as a mechanism to offset the evolutionary degradation of a transgene in three model systems: a bioreactor, a gene drive, and a transmissible vaccine. In each model, continual introduction from a stock is used to balance mutation and selection against the transgene. Each system has its unique features. The bioreactor system is especially tractable and has a simple answer: the level of supplementation required to maintain the transgene at a frequency is approximately , where s is the selective disadvantage of the transgene. Supplementation is also feasible in the transmissible vaccine case but is probably not practical to prevent the evolution of resistance against a gene drive. We note, however, that the continual replacement of even a small fraction of a large population can be challenging, limiting the usefulness of supplementation as a means of controlling unwanted evolution.

Limited genetic parallelism underlies recent, repeated incipient speciation in geographically proximate populations of an Arctic fish (Salvelinus alpinus)

The genetic underpinnings of incipient speciation, including the genomic mechanisms which contribute to morphological and ecological differentiation and reproductive isolation, remain poorly understood. The repeated evolution of consistently, phenotypically distinct morphs of Arctic Charr (Salvelinus alpinus) within the Quaternary period offer an ideal model to study the repeatability of evolution at the genomic level. Sympatric morphs of Arctic Charr are found across this species' circumpolar distribution. However, the specific genetic mechanisms driving this morph differentiation are largely unknown despite the cultural and economic importance of the anadromous morph. We used a newly designed 87k SNP chip to investigate the character and consistency of the genomic differences among sympatric morphs within three recently deglaciated and geographically proximate lakes in Labrador, Canada. We found genetically distinct small and large morph Arctic Charr in all three lakes consistent with resident and anadromous morphs, respectively. A degree of reproductive isolation among sympatric morphs is likely given genome-wide distributions of outlier SNPs and high genome-wide FSTs. Across all lakes, outlier SNPs were largely non-overlapping suggesting a lack of genetic parallelism driving morph differentiation. Alternatively, several genes and paralogous copies of the same gene consistently differentiated morphs across multiple lakes suggesting their importance to the manifestation of morphs. Our results confirm the utility of Arctic Charr as a model for investigating the predictability of evolution and support the importance of both genetic parallelism and non-parallelism to the incipient speciation of Arctic Charr morphs.

Dataset for METAPOPGEN 2.0: a multi-locus genetic simulator to model populations of large size

Multi-locus genetic processes in subdivided populations can be complex and difficult to interpret using theoretical population genetics models. Genetic simulators offer a valid alternative to study multi-locus genetic processes in arbitrarily complex scenarios. However, the use of forward-in-time simulators in realistic scenarios involving high numbers of individuals distributed in multiple local populations is limited by computation time and memory requirements. These limitations increase with the number of simulated individuals. We developed a genetic simulator, MetaPopGen 2.0, to model multi-locus population genetic processes in subdivided populations of arbitrarily large size. It allows for spatial and temporal variation in demographic parameters, age structure, adult and propagule dispersal, variable mutation rates and selection on survival and fecundity. We developed MetaPopGen 2.0 in the R environment to facilitate its use by non-modeler ecologists and evolutionary biologists. We illustrate the capabilities of MetaPopGen 2.0 for studying adaptation to water salinity in the striped red mullet Mullus surmuletus.

Weak founder effects but significant spatial genetic imprint of recent contraction and expansion of European beech populations.

Understanding the ecological and evolutionary processes occurring during species range shifts is important in the current context of global change. Here, we investigate the interplay between recent expansion, gene flow and genetic drift, and their consequences for genetic diversity and structure at landscape and local scales in European beech (Fagus sylvatica L.) On Mont Ventoux, South-Eastern France, we located beech forest refugia at the time of the most recent population minimum, approximately 150 years ago, and sampled 71 populations (2042 trees) in both refugia and expanding populations over an area of 15,000 ha. We inferred patterns of gene flow and genetic structure using 12 microsatellite markers. We identified six plots as originating from planting, rather than natural establishment, mostly from local genetic material. Comparing genetic diversity and structure in refugia versus recent populations did not support the existence of founder effects: heterozygosity (He = 0.667) and allelic richness (Ar = 4.298) were similar, and FST was low (0.031 overall). Still, significant spatial evidence of colonization was detected, with He increasing along the expansion front, while genetic differentiation from the entire pool (βWT) decreased. Isolation by distance was found in refugia but not in recently expanding populations. Our study indicates that beech capacities for colonization and gene flow were sufficient to preserve genetic diversity despite recent forest contraction and expansion. Because beech has long distance pollen and seed dispersal, these results illustrate a 'best case scenario' for the maintenance of high genetic diversity and adaptive potential under climate-change related range change.

Population genetic structure of the insular Ryukyu flying fox Pteropus dasymallus

Small isolated populations are vulnerable to both stochastic events and the negative consequences of genetic drift. For threatened species, the genetic management of such populations has therefore become a crucial aspect of conservation. Flying foxes (Pteropus spp, Chiroptera) are keystone species with essential roles in pollination and seed dispersal in tropical and subtropical ecosystems. However, many flying fox species are also threatened, having experienced dramatic population declines driven by habitat loss and hunting. The insular Ryukyu flying fox (Pteropus dasymallus) ranges from the Ryukyu Archipelago of Japan through Taiwan to the northern Philippines and has undergone precipitous population crashes on several islands in recent decades. To assess the population genetic structure and diversity in P. dasymallus, and its likely causes, we analyzed mitochondrial and microsatellite DNA. Both markers showed significant genetic differentiation among most island populations, with mitochondrial haplotypes showing some mixing across the region, likely reflecting historical colonization and/or dispersal events. In contrast, microsatellite markers showed an overall pattern of isolation by distance; however, this pattern appeared to be driven by the presence of deep ocean trenches between geographically distant populations. Thus the current distribution of P. dasymallus and its subspecific diversity appears to have arisen through vicariance coupled with a long history of restricted gene flow across oceanic barriers. We conclude that isolated island subgroups should be managed separately, with efforts directed at reducing further declines in genetic diversity.

Insights into the genetic basis of predator-induced response in Daphnia galeata

Phenotypic plastic responses allow organisms to rapidly adjust when facing environmental challenges - these responses comprise morphological, behavioral but also life-history changes. Alteration of life-history traits when exposed to predation risk have been reported often in the ecological and genomic model organism Daphnia. However, the molecular basis of this response is not well understood, especially in the context of fish predation. Here, we characterized the transcriptional profiles of two Daphnia galeata clonal lines with opposed life histories when exposed to fish kairomones. First, we conducted a differential gene expression, identifying a total of 125 candidate transcripts involved in the predator-induced response, uncovering substantial intra-specific variation. Second, we applied a gene co-expression network analysis to find clusters of tightly linked transcripts revealing the functional relations of transcripts underlying the predator-induced response. Our results showed that transcripts involved in remodeling of the cuticle, growth and digestion correlated with the response to environmental change in D. galeata. Furthermore, we used an orthology-based approach to gain functional information for transcripts lacking gene ontology (GO) information, as well as insights into the evolutionary conservation of transcripts. We could show that our candidate transcripts have orthologs in other Daphnia species but almost none in other arthropods. The unique combination of methods allowed us to identify candidate transcripts, their putative functions and evolutionary history associated with predator-induced responses in Daphnia. Our study opens up to the question as to whether the same molecular signature is associated with fish kairomones-mediated life-history changes in other Daphnia species.

opencc-zeroJan 2020View details →

Geography, seasonality, and host-associated population structure influence the fecal microbiome of a genetically depauparate Arctic mammal

The Canadian Arctic is an extreme environment with low floral and faunal diversity characterized by major seasonal shifts in temperature, moisture and daylight. Muskoxen (Ovibos moschatus) are one of few large herbivores able to survive this harsh environment. Microbiome research of the gastrointestinal tract may hold clues as to how muskoxen exist in the Arctic, but also how this species may respond to rapid environmental changes. In this study, we investigated the effects of season (spring/summer/winter), year (2007-2016), and host genetic structure on population-level microbiome variation in muskoxen from the Canadian Arctic. We utilized 16S rRNA gene sequencing to characterize the fecal microbial communities of 78 male muskoxen encompassing two population genetic clusters.<a name="_Hlk534564036"> These clusters are defined by Arctic Mainland and Island populations, including; 1) two mainland sampling locations of the Northwest Territories and Nunavut; and 2) four locations of Victoria Island. </a>Between these geographic populations, we found that differences in the microbiome reflected host-associated genetic cluster with evidence of migration. Within populations, seasonality influenced bacterial diversity with no significant differences between years of sampling. We found evidence of pathogenic bacteria, with significantly higher presence in mainland samples. Our findings demonstrate the effects of seasonality and the role of host population-level structure in driving fecal microbiome differences in a large Arctic mammal.

Strong genetic structure in a widespread estuarine crab: A test of potential versus realized dispersal

Aim: Genetic structure has proven difficult to predict for marine and estuarine species with multi-day pelagic larval durations, since many disperse far less than expected based on passive transport models. In such cases, the gap between potential and realized dispersal may result from larval behaviors that evolved to facilitate retention and settlement in favorable environments. Behavior is predicted to play a particularly key role in structuring truly estuarine species, which often moderate their behavior to remain within their natal estuaries. In such systems, this restricted dispersal may lead to high divergence, local adaptation, and eventual speciation across their range. Here, we test whether a geographically widespread estuarine crab, known to have behavior promoting larval retention, exhibits high population structure despite a 2-4 week larval duration. Location: Atlantic and Gulf Coasts of North America Taxon: White-fingered mud crab, Rhithropanopeus harrisii Methods: Population genomic analyses across nine estuaries from New Hampshire to Louisiana using 12,638 transcriptome-derived SNPs. Results: We found highly differentiated genetic signatures among all nine estuaries, separated by 200-5,000 km of coastline. Estimates of gene flow suggest that migration is low and largely symmetrical between sites. We also observed deep phylogenetic divides corresponding to major biogeographic breaks. Main conclusions: These results indicate substantial and longstanding constraints to dispersal in the species' native range, likely arising from the emergence of geological and oceanographic barriers and sustained by behavior that promotes estuarine retention during larval development. This work supports the idea that larval behavior promoting estuarine retention can be reflected in substantial genetic structure even in species with multi-week pelagic larval durations. Such behavior-restricted dispersal has implications for predicting adaptation and spread in estuarine species, many of which have been introduced outside their native ranges.

opencc-by-4.0Oct 2020View details →

zenodo36/100

Data set, combining epidemiological, genetics, and government stringency data of COVID-19 pandemic.

This data set combines epidemiological, genetics, and government stringency data of COVID-19 pandemics, all from open data sources. The sources are: Our World in Data, Worldometer, GISAID-Nextstrain, and the Oxford COVID-19 Government Response Tracker (OxCGRT). The cut off date of the first version is at the end of June 2020.  The simple data set is provided as an Excel workbook, where the first, "readme" worksheet describes the details of data of all the worksheets in the data set.  This is a working data set, expected to be refreshed over time.  Raw data are not cleaned - this collection is a tool to check various hypotheses regarding possible relations among the various data types. Simple visualisations of data relations are provided in a separate sheet.

opencc-zeroAug 2021View details →

Hare's affairs: lessons learnt from a noninvasive genetic monitoring for tracking mountain hare individuals

Systematic monitoring of individuals and their abundance over time has become an important tool to provide information for conservation. For genetic monitoring studies, noninvasive sampling has emerged as a valuable approach, particularly so for elusive or rare animals. Here, we present the five-year results of an ongoing noninvasive genetic monitoring of mountain hares (Lepus timidus) in a protected area in the Swiss Alps. We used nuclear microsatellites and a sex marker to identify individuals and assign species to noninvasively collected feces samples. Through including a marker for sex identification, we were able to assess sex-ratio changes and sex-specific demographic parameters over time. Male abundance in the area showed high fluctuations and apparent survival for males was lower than for females. Generally, males and females showed only little temporary migration into and out of the study area. Additionally, using genotyped tissue samples from mountain hares, European hares (Lepus europaeus) and their hybrids, we were able to provide evidence for the first occurrence of a European hare in the study area at an elevation of 2300 m a.s.l. in spring 2016. For future monitoring studies, we suggest to include complementary analysis methods to reliably infer species identities of the individuals analyzed and thus, not only monitor mountain hare individual abundance, but also assess the potential threats given through competitive exclusion by and hybridization with the European hare.

opencc-zeroNov 2019View details →

Data from: Genetic diversity and conservation status of Helianthus verticillatus, an endangered sunflower of the Southern United States

Evaluating species diversity and patterns of population genetic variation is an essential aspect of conservation biology to determine appropriate management strategies and preserve the biodiversity of native plants. Habitat fragmentation and potential habitat loss are often an outcome of a reduction in naturally occurring wildfires and controlled prescribed burning, as seen in Helianthus verticillatus (whorled sunflower). This endangered, wild relative of the common sunflower, Helianthus annuus, is endemic to four locations in Alabama, Georgia, and Tennessee, United States. Despite its endangered status, there is no recovery plan for H. verticillatus, and knowledge related to its basic plant biology and importance in ecosystem services is mostly unknown. In this study, we utilized 14 microsatellite loci to investigate fine-scale population structure and genetic diversity of H. verticillatus individuals found on two sampling sites within the Georgia population. Our results indicated moderate genetic diversity and the presence of two distinct genetic clusters. Analyses of molecular variance indicated that the majority of variance was individually based, thus confirming high genetic differentiation and limited gene flow between H. verticillatus collection sites. The evidence of a population bottleneck in these sites suggests a recent reduction in population size that could be explained by habitat loss and population fragmentation. Also, high levels of linkage disequilibrium were detected, putatively suggesting clonal reproduction among these individuals. Our study provides a better understanding of fine-scale genetic diversity and spatial distribution of H. verticillatus populations in Georgia. Our results can underpin an original recovery plan for H. verticillatus that could be utilized for the conservation of this endangered species and to promote its persistence in the wild.

A chromosome-scale reference genome and genome-wide genetic variations elucidate adaptation in yak

Yak is an important livestock for the people who lived in harsh and oxygen-deprived Qinghai-Tibetan Plateau and Hindu-Kush Himalayan Mountains. Although there is a yak genome be sequenced in 2012, the assembly is quite fragmented due to the limitation of Illumina sequencing technology. An accurate and complete reference genome is critical for studying genetic variation of a specie. Long-read sequences are more complete than short-read ones, and they have been successfully used for high-quality genome assembly in several species. Here, we present a high-quality assembly of the yak genome (PB_v1.0) at chromosome scale, which was constructed using long-read sequencing technology assisted by chromatin interaction technology. Compared to the previous yak genome assembly (BosGru_v2.0), the PB_v1.0 assembly has substantially improved chromosome sequence continuity, minimized repetitive structure ambiguity, and achieved gene model completeness. To intensively characterize genetic variation of yak, we generated de novo genome assemblies based on Illumina short reads of seven recognized domestic yak breeds from Tibet and Sichuan as well as one wild yak from Hoh Xil. By comparing these eight assemblies to the PB_v1.0 genome, we obtained a comprehensive map of yak genetic diversity at whole genome level and identified a few protein-coding genes that were absent from the PB_v1.0 assembly. Although wild yak suffered bottleneck effect, the genetic diversity of wild yak is still higher than that of domestic yak. By whole genome alignment, we identified breed-specific sequences and genes, this will help the breeds identification of yak.

opencc-zeroNov 2020View details →

Genetic variants beyond amyloid and tau associated cognitive decline: a cohort study

Objective: To identify single nucleotide polymorphisms (SNPs) associated with cognitive decline independent of amyloid &[beta] (A&[beta]) and tau pathology in Alzheimer's disease (AD). Methods: Discovery and replication datasets consisting of 414 subjects (94 cognitively normal control [CN), 185 with mild cognitive impairment [MCI], and 135 AD) and 72 subjects (22 CN, 39 MCI, and 11 AD), respectively, were obtained from the Alzheimer's Disease Neuroimaging Initiative database. Genome-wide association analysis was conducted to identify SNPs associated with individual cognitive function (measured using the MMSE and ADAS-cog) while controlling for the level of A&[beta] and tau (measured as CSF p-tau/A&[beta]1-42). Gene ontology analysis was performed on SNP associated genes. Results: We identified one significant (rs55906536, &[beta]=-1.91,standard error 0.34, P =4.07×10-8) and four suggestive variants on chromosome 6, which were associated with poorer cognitive function. Congruent results were found in the replication data. A structural equation model showed that the identified SNP deteriorated cognitive function partially through cortical thinning of the brain in a region-specific manner. Furthermore, a bioinformatics analysis showed that the identified SNPs were associated with genes related to glutathione metabolism. Conclusions: In this study, we identified SNPs related to cognitive decline, in a manner which could not be explained by A&[beta] and tau levels. Our findings provide insight into the complexity of AD pathogenesis and support the growing literature on the role of glutathione in AD. This study suggests anti-oxidative agents may serve therapeutic for AD subjects with the identified SNPs.

opencc-zeroNov 2020View details →

Mixed-stock analysis using Rapture genotyping to evaluate stock-specific exploitation of a walleye population despite weak genetic structure

Mixed-stock analyses using genetic markers have informed fisheries management in cases where strong genetic differentiation occurs among local spawning populations, yet many fisheries are supported by multiple spawning stocks that are weakly differentiated. Freshwater fisheries exemplify this problem, with many harvested populations supported by multiple stocks of young evolutionary age and that are isolated across small spatial scales. As a result, attempts to conduct genetic mixed-stock analyses of inland fisheries have often been unsuccessful. Advances in genomic sequencing now offer the ability to discriminate among populations with weak population structure, by providing the necessary resolution to conduct mixed-stock assignment among previously indistinguishable stocks. We demonstrate the use of genomic data to conduct a mixed-stock analysis of Lake Erie's commercial and recreational walleye (Sander vitreus) fisheries and estimate the relative harvest of weakly differentiated stocks. We used RAD-capture (Rapture) to sequence and genotype individuals at 12,081 loci that had been previously determined to be capable of discriminating between western and eastern basin stocks (mean pairwise FST = 0.001) with 95% reassignment accuracy. An outcome not possible in the past with microsatellite markers. Genetic assignment of 1,075 fish harvested from recreational and commercial fisheries in the eastern basin indicated that western basin stocks supported the majority of the harvest during peak harvest (July – September). Composition of harvest changed seasonally, with eastern basin fish comprising much of the early season harvest (May – June). Clear spatial structure in stock-specific harvest existed; more easterly sites contained more individuals of east basin origin than did westerly sites. Our study provides important stock contribution estimates for Lake Erie fishery management and demonstrates the power of genomic data to facilitate mixed-stock analysis in exploited fish populations with weak population structure or limited existing genetic resources.

opencc-zeroDec 2019View details →

Data for: Coevolution fails to maintain genetic variation in a host-parasite model with constant finite population size

Coevolutionary negative frequency-dependent selection has been hypothesized to maintain genetic variation in host and parasites. Despite the extensive literature pertaining to host-parasite coevolution, the dynamics of genetic variation has not been examined in a matching-alleles model (MAM) with a finite population size relative to the expectation under neutral genetic drift alone. The dynamics of the MA coevolution in an infinite population, in fact, suggests that genetic variation in these coevolving populations behaves neutrally. By comparing host heterozygosity to the expectation in a single-species model of neutral genetic drift we find that while this is also largely true in finite populations two additional phenomena arise. First, reciprocal natural selection acting on stochastic perturbations in host and pathogen allele frequencies results in a slight increase or decrease in genetic variation depending on the parameter conditions. Second, following the fixation of an allele in the parasite, selection in the MAM becomes directional, which then rapidly erodes genetic variation in the host. Hence, rather than maintain it, we find that, on average, matching-alleles coevolution depletes genetic variation.