Changes In Genetic Diversity Research Articles

Changing environments and genetic variation: natural variation in inbreeding does not compromise short-term physiological responses.

Selfing plant lineages are surprisingly widespread and successful in a broad range of environments, despite showing reduced genetic diversity, which is predicted to reduce their long-term evolutionary potential. However, appropriate short-term plastic responses to new environmental conditions might not require high levels of standing genetic variation. In this study, we tested whether mating system variation among populations, and associated changes in genetic variability, affected short-term responses to environmental challenges. We compared relative fitness and metabolome profiles of naturally outbreeding (genetically diverse) and inbreeding (genetically depauperate) populations of a perennial plant, Arabidopsis lyrata, under constant growth chamber conditions and an outdoor common garden environment outside its native range. We found no effect of inbreeding on survival, flowering phenology or short-term physiological responses. Specifically, naturally occurring inbreeding had no significant effects on the plasticity of metabolome profiles, using either multivariate approaches or analysis of variation in individual metabolites, with inbreeding populations showing similar physiological responses to outbreeding populations over time in both growing environments. We conclude that low genetic diversity in naturally inbred populations may not always compromise fitness or short-term physiological capacity to respond to environmental change, which could help to explain the global success of selfing mating strategies.

Estimated six per cent loss of genetic variation in wild populations since the industrial revolution.

Genetic variation is fundamental to population fitness and adaptation to environmental change. Human activities are driving declines in many wild populations and could have similar effects on genetic variation. Despite the importance of estimating such declines, no global estimate of the magnitude of ongoing genetic variation loss has been conducted across species. By combining studies that quantified recent changes in genetic variation across a mean of 27 generations for 91 species, we conservatively estimate a 5.4%–6.5% decline in within‐population genetic diversity of wild organisms since the industrial revolution. This loss has been most severe for island species, which show a 27.6% average decline. We identified taxonomic and geographical gaps in temporal studies that must be urgently addressed. Our results are consistent with single time‐point meta‐analyses, which indicated that genetic variation is likely declining. However, our results represent the first confirmation of a global decline and provide an estimate of the magnitude of the genetic variation lost from wild populations.

Evaluation of recent changes in genetic variability in Japanese thoroughbred population based on a short tandem repeat parentage panel.

The integrity of thoroughbreds is maintained under strict regulation involving DNA parentage testing, which is robust in a population with high genetic variability. The genetic variability of the thoroughbred population is possibly fluctuating because of selective breeding that has focused on adaptations for racing performance. To monitor genetic variability within the population and the effectiveness of short tandem repeat (STR) parentage testing, we investigated allele frequencies and the exclusion probability (PE) of 16-17 loci of a parentage panel in the Japanese thoroughbred population over 15years. Expected heterozygosities (He) of 14 loci indicated a decreasing trend, and the average He of the population decreased significantly. Low genetic variability was possibly induced by a decrease in population size and a selective breeding bias. Four loci showed both a significant increase in allele frequency and a significant decrease in He; it is assumed that those loci were affected by positive selection for racing performance. There was a significant decrease in the PE because of the changes in genetic variability; however, it has remained over 0.99995. The current STR panel is still effective for parentage control, but it will be necessary to continuously monitor genetic variability, which has decreased over 15years.

Cultural hitchhiking and competition between patrilineal kin groups explain the post-Neolithic Y-chromosome bottleneck

In human populations, changes in genetic variation are driven not only by genetic processes, but can also arise from cultural or social changes. An abrupt population bottleneck specific to human males has been inferred across several Old World (Africa, Europe, Asia) populations 5000–7000 BP. Here, bringing together anthropological theory, recent population genomic studies and mathematical models, we propose a sociocultural hypothesis, involving the formation of patrilineal kin groups and intergroup competition among these groups. Our analysis shows that this sociocultural hypothesis can explain the inference of a population bottleneck. We also show that our hypothesis is consistent with current findings from the archaeogenetics of Old World Eurasia, and is important for conceptions of cultural and social evolution in prehistory.

Trait Response and Change in Genetic Variation upon Selection for Spike Number in Salina Wildrye

Salina wildrye (Leymus salinus [M.E. Jones] Á. Löve) is a perennial cool-season grass that potentially could become an important restoration species in the Colorado Plateau. However, its seed production has never been commercially viable due to sparse heading. We compared a 4x ssp. salmonis population, Lakeside C3, to an 8x ssp. salinus population, 9043501, for seed production−related traits and measured the response of 9043501 to 2 cycles of selection for increased spike number over a 4-yr period at Millville, Utah. Seed yield of Lakeside and 9043501 was similar (P > 0.10) in 2013, but seed yield of 9043501 was 81% greater (P < 0.10) than Lakeside in 2014 and 191% greater (P < 0.01) in 2015. Lakeside spike number was 99% greater (P < 0.0001) than 9043501 in 2013, but they were similar (P > 0.10) in 2014 and 2015. Seeds per spike of 9043501 were 71% (P < 0.05), 80% (P < 0.05), and 209% (P < 0.01) greater than Lakeside in 2013, 2014, and 2015, respectively. Selection in 9043501 increased (P < 0.05) spike number by 4.3 spikes per plant (19.8%) per cycle of selection in the first seed-production yr (2013), but no change was seen in 2014 or 2015 (P > 0.10). Selection did not change (P > 0.10) seeds per spike or individual seed mass. Consequently, seed yield increased (P < 0.05) 0.32 g per plant per cycle (36.8%) in 2013, with no increase (P > 0.10) in 2014 or 2015. Dry matter per plant across the 4 yr increased (P < 0.01) 10.3 g per plant per cycle (9.3%), and canopy height increased (P < 0.01) 3.9 cm per cycle (6.6%) in 2013. AFLP DNA primers detected a 1.7% loss of genetic variation per cycle, presumably due to a combination of selection and genetic drift, but no plant traits were diminished as a result.

Temporal changes in genetic variability in three bumblebee species from Rio Grande do Sul, South Brazil

In order to protect biodiversity, conservation genetics are of great importance. Until now, a few population genetic studies of Neotropical bumblebees are available but studies of temporal stability in genetic diversity are lacking. Here, genetic variability of three South Brazilian species Bombus bellicosus, B. pauloensis, and B. morio was investigated over time. Hereto, museum collection specimens of 1946 until 2012, from eight locations in Rio Grande do Sul, were genotyped at 16 microsatellite loci. During an additional sampling in the foraging season of 2015, no bumblebees could be collected possibly due to the super El Nino of 2015–2016. Our results on the collection specimens demonstrated a significantly higher genetic diversity in B. morio than in B. pauloensis. Genetic variability in B. pauloensis gradually and significantly decreased over time from 1946 until 2012; while in B. morio, genetic variability remained stable until the last time period (2010–2012). For B. bellicosus, not enough data was available. Although the studied populations became more vulnerable over time, for the conservation of Neotropical bumblebees, still more information is needed and could include more frequent monitoring of bumblebees. Adding B. bellicosus to the Brazilian list of threatened species is suggested.

Genomic data reveal a loss of diversity in two species of tuco-tucos (genus Ctenomys) following a volcanic eruption

Marked reductions in population size can trigger corresponding declines in genetic variation. Understanding the precise genetic consequences of such reductions, however, is often challenging due to the absence of robust pre- and post-reduction datasets. Here, we use heterochronous genomic data from samples obtained before and immediately after the 2011 eruption of the Puyehue-Cordón Caulle volcanic complex in Patagonia to explore the genetic impacts of this event on two parapatric species of rodents, the colonial tuco-tuco (Ctenomys sociabilis) and the Patagonian tuco-tuco (C. haigi). Previous analyses using microsatellites revealed no post-eruption changes in genetic variation in C. haigi, but an unexpected increase in variation in C. sociabilis. To explore this outcome further, we used targeted gene capture to sequence over 2,000 putatively neutral regions for both species. Our data revealed that, contrary to the microsatellite analyses, the eruption was associated with a small but significant decrease in genetic variation in both species. We suggest that genome-level analyses provide greater power than traditional molecular markers to detect the genetic consequences of population size changes, particularly changes that are recent, short-term, or modest in size. Consequently, genomic analyses promise to generate important new insights into the effects of specific environmental events on demography and genetic variation.

Environmental stress correlates with increases in both genetic and residual variances: A meta-analysis of animal studies.

Adaptive evolutionary responses are determined by the strength of selection and amount of genetic variation within traits, however, both are known to vary across environmental conditions. As selection is generally expected to be strongest under stressful conditions, understanding how the expression of genetic variation changes across stressful and benign environmental conditions is crucial for predicting the rate of adaptive change. Although theory generally predicts increased genetic variation under stress, previous syntheses of the field have found limited support for this notion. These studies have focused on heritability, which is dependent on other environmentally sensitive, but nongenetic, sources of variation. Here, we aim to complement these studies with a meta-analysis in which we examine changes in coefficient of variation (CV) in maternal, genetic, and residual variances across stressful and benign conditions. Confirming previous analyses, we did not find any clear direction in how heritability changes across stressful and benign conditions. However, when analyzing CV, we found higher genetic and residual variance under highly stressful conditions in life-history traits but not in morphological traits. Our findings are of broad significance to contemporary evolution suggesting that rapid evolutionary adaptive response may be mediated by increased evolutionary potential in stressed populations.

Rapid increase in genetic diversity in an endemic Patagonian tuco-tuco following a recent volcanic eruption

Catastrophic natural events can have profound impacts on patterns of genetic diversity. Due to the typically unpredictable nature of such phenomena, however, few studies have been able to directly compare patterns of diversity before and after natural catastrophic events. Here, we examine the impacts of a recent volcanic eruption in southern Chile on genetic variation in the colonial tuco-tuco (Ctenomys sociabilis), a subterranean species of rodent endemic to the area most affected by the June 2011 eruption of the Puyehue-Cordon Caulle volcanic complex. To provide a comparative context for interpreting changes in genetic variation in this species, we also analyze the effects of this eruption on genetic variation in the geographically proximate but more widely distributed Patagonian tuco-tuco (C. haigi). Our analyses indicate that while both C. sociabilis and C. haigi displayed significant post-eruption decreases in population density, the apparent impacts of the eruption on genetic diversity differed between species. In particular, genetic diversity at multiple microsatellite loci increased in C. sociabilis after the eruption while no comparable post-eruption increase in C. haigi was observed at these loci. No changes in post-eruption diversity at the mitochondrial cytochrome b locus were detected for either species. To place these findings in a larger spatiotemporal context, we compared our results for C. sociabilis to genetic data from additional modern and ancient populations of this species. These comparisons, combined with Bayesian serial coalescent modeling, suggest that post-eruption gene flow from nearby populations represents the most probable explanation for the apparent increase in post-eruption microsatellite diversity in C. sociabilis. Thus, detailed comparisons of pre- and post-eruption populations provide important insights into not only the genetic consequences of a natural catastrophic event, but also the demographic processes by which these changes in genetic diversity likely occurred.

On the Long-term Stability of Clines in Some Metabolic Genes in Drosophila melanogaster

Very little information exists for long-term changes in genetic variation in natural populations. Here we take the unique opportunity to compare a set of data for SNPs in 15 metabolic genes from eastern US collections of Drosophila melanogaster that span a large latitudinal range and represent two collections separated by 12 to 13 years. We also expand this to a 22-year interval for the Adh gene and approximately 30 years for the G6pd and Pgd genes. During these intervals, five genes showed a statistically significant change in average SNP allele frequency corrected for latitude. While much remains unchanged, we see five genes where latitudinal clines have been lost or gained and two where the slope significantly changes. The long-term frequency shift towards a southern favored Adh S allele reported in Australia populations is not observed in the eastern US over a period of 21 years. There is no general pattern of southern-favored or northern-favored alleles increasing in frequency across the genes. This observation points to the fluid nature of some allelic variation over this time period and the action of selective responses or migration that may be more regional than uniformly imposed across the cline.

Highly Connected Populations and Temporal Stability in Allelic Frequencies of a Harvested Crab from the Southern Pacific Coast.

For marine invertebrates with a benthic adult form and a planktonic larva phase, the connectivity among populations is mainly based on larval dispersal. While an extended larval phase will promote gene flow, other factors such as an intensive fishery and geographical barriers could lead to changes in genetic variability. In this study, the population genetic structure of the commercial crab Metacarcinus edwardsii was analyzed along 700 km of the Chilean coast. The analysis, based on eight microsatellite loci genotyped from megalopae and adult crabs, considered temporal and spatial patterns of genetic variation. The results showed no evidence of spatial patterns in genetic structure, suggesting high connectivity among the sampling sites. The temporal analysis showed no evidence of changes in allele frequencies and no evidence of a recent bottleneck. The lack of spatial structure and allele variation over time could be explained by the interaction of factors such as i) low reproductive variance due to the capability of females to store sperm in the seminal receptacle, which can be used for successive broods, ii) high larval dispersal and iii) high individual reproductive output. Using our data as priors, a genetic modelling approach coincided, predicting this temporal and spatial stability. The same analysis showed that a reduction in population size leads to the loss of genetic variability in populations, as well as of the genetic cohesiveness between populations, pointing out the importance management for species under exploitation, such as M. edwardsii.

Comparison of old and new wheat cultivars in Iran by measuring germination related traits, osmotic tolerance and ISSR diversity.

A primary concern of modern plant breeding is that genetic diversity has decreased during the past century. This study set out to explore changes in genetic variation during 84years of breeding by investigating the germination-related traits, inter-simple sequence repeat (ISSR) fingerprinting and osmotic stress tolerance of 30 Iranian wheat (Triticum aestivum L.) cultivars. Seeds were planted under control and osmotic stress (-2, -4 and -6bar) in three replications. The ISSR experiment was carried out using 32 different primers. Genotypes were divided into two groups (old and new) each containing 15 members. The results of ANOVA showed that highly significant differences existed among genotypes and among growth conditions. The results showed that during breeding in some traits such as coleoptile length and seedling vigor index, a significant decrease has been occurred. New cultivars had a mean coleoptile length of 33mm, shorter than that of old cultivars (42mm) under osmotic stress of -6bar. Genetic variance of root length, shoot length and seedling vigor index for old cultivars were 1.59, 1.93 and 45,763, respectively, significantly higher than those for new cultivars (0.55, 1.08 and 27,996, respectively). This difference was also verified by ISSR results as the polymorphism information content was 0.28 in old cultivars, higher than that of new cultivars (0.26). These results prove this claim that during breeding, genetic diversity has decreased for many germination-related traits and breeders are better to pay more attention to genetic diversity.

High genetic variation among closely related red oak (Quercus rubra) populations in an ecosystem under metal stress: analysis of gene regulation

Metal toxicity is a major abiotic stressor of plants. It has been established that changes in genetic variation occur very rapidly in plants in response to environmental stressors such as increased levels of metals. Quercus rubra (red oak) is a pioneer species in mining regions contaminated with metals in Northern Ontario (Canada). The objectives of the study were to (1) determine the level of genetic variation in Q. rubra populations from mining damaged ecosystems using RAPD marker system and (2) assess the level of gene expression of candidate genes for nickel resistance. Total gene diversity (HT) and the mean gene diversity among populations (HS) were 0.22 and 0.19, respectively. The percent of polymorphic loci within populations was high ranging from 61 % (Capreol) to 72 % (Daisy Lake) despite a high level of gene flow (2.4). The population differentiation (GST) value was low (0.17). No significant difference was found among the contaminated and reference sites for all the genetic parameters estimated. Hence, all the Q. rubra populations from the metal-contaminated and damaged ecosystems are genetically sustainable. Moreover, this study reveals that all populations were genetically closely related with genetic distance values varying from 0.17 to 0.35. A zinc finger protein of Arabidopsis thaliana (ZAT11) gene involved in nickel resistance was differentially expressed in samples analyzed. There was a 120 times higher of ZAT11 expression in samples from metal contaminated areas of Wahnapitae Dam compared to other metal contaminated and uncontaminated sites, but no association between soil metal levels and expression of ZAT11 was established.

Application of a dense genetic map for assessment of genomic responses to selection and inbreeding in Heliothis virescens.

Adaptation of pest species to laboratory conditions and selection for resistance to toxins in the laboratory are expected to cause inbreeding and genetic bottlenecks that reduce genetic variation. Heliothis virescens, a major cotton pest, has been colonized in the laboratory many times, and a few laboratory colonies have been selected for Bacillus thuringiensis (Bt) resistance. We developed 350-bp double-digest restriction-site associated DNA-sequencing (ddRAD-seq) molecular markers to examine and compare changes in genetic variation associated with laboratory adaptation, artificial selection and inbreeding in this nonmodel insect species. We found that allelic and nucleotide diversity declined dramatically in laboratory-reared H.virescens as compared with field-collected populations. The declines were primarily a result of the loss of low frequency alleles present in field-collected H.virescens. A further, albeit modest decline in genetic diversity was observed in a Bt-selected population. The greatest decline was seen in H.virescens that were sib-mated for 10 generations, in which more than 80% of loci were fixed for a single allele. To determine which regions of the genome were resistant to fixation in our sib-mated line, we generated a dense intraspecific linkage map containing three PCR-based and 659 ddRAD-seq markers. Markers that retained polymorphism were observed in small clusters spread over multiple linkage groups, but this clustering was not statistically significant. Overall, we have confirmed and extended the general expectations for reduced genetic diversity in laboratory colonies, provided tools for further genomic analyses and produced highly homozygous genomic DNA for future whole genome sequencing of H.virescens.

The genetic underpinnings of population cyclicity: establishing expectations for the genetic anatomy of cycling populations

Despite extensive research into the mechanisms underlying population cyclicity, we have little understanding of the impacts of numerical fluctuations on the genetic variation of cycling populations. Thus, the potential implications of natural and anthropogenically‐driven variation in population cycle dynamics on the diversity and evolutionary potential of cyclic populations is unclear. Here, we use Canada lynx Lynx canadensis matrix population models, set up in a linear stepping‐stone, to generate demographic replicates of biologically realistic cycling populations. Overall, increasing cycle amplitude predictably reduced genetic diversity and increased genetic differentiation, with cyclic effects increased by population synchrony. Modest dispersal rates (1–3% of the population) between high and low amplitude cyclic populations did not diminish these effects suggesting that spatial variation in cyclic amplitude should be reflected in patterns of genetic diversity and differentiation at these rates. At high dispersal rates (6%) groups containing only high amplitude cyclic populations had higher diversity and lower differentiation than those mixed with low amplitude cyclic populations. Negative density‐dependent dispersal did not impact genetic diversity, but did homogenize populations by reducing differentiation and patterns of isolation by distance. Surprisingly, temporal changes in diversity and differentiation throughout a cycle were not always consistent with population size. In particular, negative density‐dependent dispersal simultaneously decreased differences in genetic diversity while increasing differences in genetic differentiation between numerical peaks and nadirs. Combined, our findings suggest demographic changes at fine temporal scales can impact genetic variation of interacting populations and provide testable predictions relating population cyclicty to genetic variation. Further, our results suggest that including realistic demographic and dispersal parameters in population genetic models and using information from temporal changes in genetic variation could help to discern complex demographic scenarios and illuminate population dynamics at fine temporal scales.

Assessing Biological Impacts of Land Reclamation in a Mining Region in Canada: Effects of Dolomitic Lime Applications on Forest Ecosystems and Microbial Phospholipid Fatty Acid Signatures

The ability of an ecosystem to withstand serious disturbances may depend in part on the diversity of the system, with soil microbiological communities being coupled to their associated vegetation. The main objectives of the present study were (1) to determine the association between soil microbial diversity, abundance, and activities with diversity and sustainability of remediated mining-damaged ecosystems in Northern Ontario, and (2) to assess the effects of dolomitic lime applications on aboveground and belowground biodiversity and community structures. Results revealed that liming increases soil pH, cation exchange capacity (CEC), forest tree species diversity and abundance, and the overall ecosystem health even 25 to 35 years after dolomite applications. The mean Shannon index value was significantly higher in limed compared to unlimed sites. Tree species richness was 4.0, 6.0, and 7.7 for unlimed, limed, and reference sites, respectively. Overall, the mean health index revealed a significant improvement in population health in limed sites (index score = 7) compared to unlimed areas (index score = 4). Soil microbial biomass and respiration were also increased by liming. Surprisingly, the main component of soil microbial biomass in limed, unlimed, and reference sites within the vicinity of the restored lands was bacteria (mostly Gram (−). Significant difference was also observed between limed, unlimed, and reference sites for arbuscular mycorrhizal fungi, Gram (−) bacteria, Gram (+) bacteria, anaerobe, and actinomycetes abundance. The ratios between fungi and bacteria and among other phospholipid fatty acid (PLFA) measures were extremely low suggesting that the targeted region is still under environmental stress. No apparent associations among soil microbial biomass, soil respiration, and forest plant diversity or abundance were observed. Soil pH levels and organic matter amounts and quality appear to be the main factors affecting these parameters. Molecular analysis of main tree species within the impacted region revealed no change in genetic variation among plant populations on either limed or unlimed lands contaminated with metals over two generations.

Revealing the consequences of male-biased trophy hunting on the maintenance of genetic variation

Demographic models accounting for operational sex ratio (OSR) show that male numbers can have a substantial influence on the dynamics of wild populations. We used the Cantabrian capercaillie, a forest bird, as a model to assess the effects of the reduction in the number of breeding males (increased OSR) associated to male-biased hunting, on the genetics of the population. We based our assessment in the comparison of the dynamics of neutral markers transmitted by both parents (microsatellites) versus markers transmitted only by females (mitochondrial DNA—mtDNA). Parallel to the analysis of field data, we ran computer simulations to explore how different levels of OSR and two other important demographic factors, population size and connectivity, might influence the dynamics of genetic variation of microsatellites and mtDNA. We found evidence of a genetic bottleneck and low genetic variability affecting microsatellites but not mtDNA early in our study period, when male-biased hunting was more intense. This was followed by a decline in mtDNA variation around 10–20 years later. Simulations suggested that changes in genetic variation associated with high OSR had the closest similarity to those observed at the beginning of our study, whereas a combination of reduced size and migration rate better resembled the patterns found later on. Our findings indicate that male-biased hunting might have triggered the ongoing decline of the Cantabrian capercaillie, on its own or in combination with habitat configuration, and support the need to incorporate OSR into decision making for the management and conservation of exploited populations.

Expression of parasite genetic variation changes over the course of infection: implications of within-host dynamics for the evolution of virulence.

How infectious disease agents interact with their host changes during the course of infection and can alter the expression of disease-related traits. Yet by measuring parasite life-history traits at one or few moments during infection, studies have overlooked the impact of variable parasite growth trajectories on disease evolution. Here we show that infection-age-specific estimates of host and parasite fitness components can reveal new insight into the evolution of parasites. We do so by characterizing the within-host dynamics over an entire infection period for five genotypes of the castrating bacterial parasite Pasteuria ramosa infecting the crustacean Daphnia magna. Our results reveal that genetic variation for parasite-induced gigantism, host castration and parasite spore loads increases with the age of infection. Driving these patterns appears to be variation in how well the parasite maintains control of host reproduction late in the infection process. We discuss the evolutionary consequences of this finding with regard to natural selection acting on different ages of infection and the mechanism underlying the maintenance of castration efficiency. Our results highlight how elucidating within-host dynamics can shed light on the selective forces that shape infection strategies and the evolution of virulence.

Dynamics of genetic variability in Anastrepha fraterculus (Diptera: Tephritidae) during adaptation to laboratory rearing conditions.

BackgroundAnastrepha fraterculus is one of the most important fruit fly plagues in the American continent and only chemical control is applied in the field to diminish its population densities. A better understanding of the genetic variability during the introduction and adaptation of wild A. fraterculus populations to laboratory conditions is required for the development of stable and vigorous experimental colonies and mass-reared strains in support of successful Sterile Insect Technique (SIT) efforts.MethodsThe present study aims to analyze the dynamics of changes in genetic variability during the first six generations under artificial rearing conditions in two populations: a) a wild population recently introduced to laboratory culture, named TW and, b) a long-established control line, named CL.ResultsResults showed a declining tendency of genetic variability in TW. In CL, the relatively high values of genetic variability appear to be maintained across generations and could denote an intrinsic capacity to avoid the loss of genetic diversity in time.DiscussionThe impact of evolutionary forces on this species during the adaptation process as well as the best approach to choose strategies to introduce experimental and mass-reared A. fraterculus strains for SIT programs are discussed.

Population structure and recent temporal changes in genetic variation in Eurasian otters from Sweden

The Eurasian otter (Lutra lutra) population in Sweden went through a drastic decline in population size between the 1950s and 1980s, caused mostly by anthropogenic factors such as high hunting pressure and the introduction of environmental toxic chemicals into the otter’s habitats. However, after the bans of PCBs and DDT in the 1970s, the population began to recover in the 1990s. This study compares microsatellite data across twelve loci from historical and contemporary otter samples to investigate whether there has been a change in population structure and genetic diversity across time in various locations throughout Sweden. The results suggest that otters in the south were more severely affected by the bottleneck, demonstrated by a decline in genetic diversity and a shift in genetic composition. In contrast, the genetic composition in otters from northern Sweden remained mostly unchanged, both in terms of population structure and diversity. This suggests that the decline was not uniform across the country. Moreover, our analyses of historical samples provide an overview of the level of genetic variation and population structure that existed prior to the bottleneck, which may be helpful for the future management and conservation of the species.