Genetic Admixture Research Articles

Urbanization-associated range expansion genetically homogenizes a butterfly species

Human-induced environmental change and globalization facilitate biological invasions, which can lead to the displacement of native species by non-native ones.1,2,3,4 Analogously, biodiversity loss may occur within species when habitat modifications facilitate the expansion of a specific population's range, leading to genetic admixture with native local populations. We demonstrate such intraspecific loss in population-level diversity in the Southern Small White (Pieris mannii), an originally sedentary butterfly5 that recently expanded its range across Central Europe due to urbanization.6,7,8 Using genome-wide markers from historical museum specimens and contemporary samples, we identify a distinct population initiating this expansion and reveal the genetic homogenization of native local populations by admixture with the expansive one. Our study illustrates how human-made environmental change can simultaneously benefit a species by permitting range expansion and drive cryptic biodiversity loss through the genetic homogenization of conspecific populations.

Phylogeographic analysis reveals multiple origins of the desert shrub Reaumuria songarica in northern Xinjiang, involving homoploid and tetraploid hybrids.

Hybrid speciation plays an important role in species diversification. The establishment of reproductive isolation is crucial for hybrid speciation, and the identification of diverse types of hybrids, particularly homoploid hybrid species, contributes to a comprehensive understanding of this process. Reaumuria songarica is a constructive shrub widespread in arid Central Asia. Previous studies have inferred that the R. songarica populations in the Gurbantunggut Desert (GuD) originated from homoploid hybridizations between its eastern and western lineages and may have evolved into an incipient species. To further elucidate the genetic composition of different hybrid populations and to determine the species boundary of this hybrid lineage, we investigated the overall phylogeographic structure of R. songarica based on variation patterns of five cpDNA and one nrITS sequences across 32 populations. Phylogenetic analyses demonstrated that within the GuD lineage, the Wuerhe population evolved directly from ancestral lineages, whereas the others originated from hybridizations between the eastern and western lineages. PCoA and genetic barrier analysis supported the subdivision of the GuD lineage into the southern (GuD-S) and northern (GuD-N) groups. Populations in the GuD-S group had a consistent genetic composition and the same ancestral female parent, indicating that they belonged to a homoploid hybrid lineage. However, the GuD-N group experienced genetic admixture of the eastern and western lineages on nrITS and cpDNA, with some populations inferred to be allopolyploid based on ploidy data. Based on cpDNA haplotypes, BEAST analyses showed that the GuD-S and GuD-N groups originated after 0.5 Ma. Our results suggest that multiple expansions and contractions of GuD, driven by Quaternary climatic oscillations and the Kunlun-Yellow River tectonic movement, are important causes of the complex origins of R. songarica populations in northern Xinjiang. This study highlights the complex origins of the Junggar Basin flora and the underappreciated role of hybridization in increasing its species diversity.

Genetic and telomeric variability: Insights from a tropical avian hybrid zone.

Telomere lengths and telomere dynamics can correlate with lifespan, behaviour and individual quality. Such relationships have spurred interest in understanding variation in telomere lengths and their dynamics within and between populations. Many studies have identified how environmental processes can influence telomere dynamics, but the role of genetic variation is much less well characterized. To provide a novel perspective on how telomeric variation relates to genetic variability, we longitudinally sampled individuals across a narrow hybrid zone (n = 127 samples), wherein two Manacus species characterized by contrasting genome-wide heterozygosity interbreed. We measured individual (n = 66) and population (n = 3) differences in genome-wide heterozygosity and, among hybrids, amount of genetic admixture using RADseq-generated SNPs. We tested for population differences in telomere lengths and telomere dynamics. We then examined how telomere lengths and telomere dynamics covaried with genome-wide heterozygosity within populations. Hybrid individuals exhibited longer telomeres, on average, than individuals sampled in the adjacent parental populations. No population differences in telomere dynamics were observed. Within the parental population characterized by relatively low heterozygosity, higher genome-wide heterozygosity was associated with shorter telomeres and higher rates of telomere shortening-a pattern that was less apparent in the other populations. All of these relationships were independent of sex, despite the contrasting life histories of male and female manakins. Our study highlights how population comparisons can reveal interrelationships between genetic variation and telomeres, and how naturally occurring hybridization and genome-wide heterozygosity can relate to telomere lengths and telomere dynamics.

Prevalence of cardiovascular autonomic neuropathy in an admixed population of patients with type 1 diabetes. Lessons from a pioneer multicentre study in Brazil

AIMSTo evaluate the prevalence of cardiovascular autonomic neuropathy (CAN) and its associated factors in Brazilian patients with type 1 diabetes (T1D). MethodsThis cross-sectional, multicentre study was conducted in 14 public clinics in ten Brazilian cities. From 1760 patients, 1712 were included (97.3 %): 953 females (55.7 %), 930 (54.3 %) Caucasians, aged 29.9 ±11.9 years and with diabetes duration of 15.4 ± 9.2 years. CAN was evaluated using cardiovascular autonomic reflex tests. ResultsThe prevalence of CAN was 23.4 %. Multivariable hierarchical logistic regression showed CAN associated with age, smoking, lower socioeconomic status, higher yearly medical appointments, insulin therapeutic regimens, higher levels of HbA1c, total cholesterol, uric acid, diastolic blood pressure and heart rate, presence of retinopathy, diabetic kidney disease and a tendency to be associated with severe hypoglycemia. Lower health-related quality of life was also found in univariate analysis in these patients. ConclusionsPatients with T1D presented an important prevalence of CAN that was associated with other diabetes-related chronic complications, and also with demographic, clinical and laboratorial traditional risk factors. Considering lack of formal policy, our data could be used for guiding public health approach to awareness and CAN’s screening, diagnosis and clinical management in patients with T1D in Brazil.

Genomic dynamics of the Lower Yellow River Valley since the Early Neolithic

The Yellow River Delta played a vital role in the development of the Neolithic civilization of China. However, the population history of this region from the Neolithic transitions to the present remains poorly understood due to the lack of ancient human genomes. This especially holds for key Neolithic transitions and tumultuous turnovers of dynastic history. Here, we report genome-wide data from 69 individuals dating to 5,410-1,345 years before present (BP) at 0.008 to 2.49× coverages, along with 325 present-day individuals collected from 16 cities across Shandong. During the Middle to Late Dawenkou period, we observed a significant influx of ancestry from Neolithic Yellow River farmers in central China and some southern Chinese ancestry that mixed with local hunter-gatherers in Shandong. The genetic heritage of the Shandong Longshan people was found to be most closely linked to the Dawenkou culture. During the Shang to Zhou Dynasties, there was evidence of genetic admixture of local Longshan populations with migrants from the Central Plain. After the Qin to Han Dynasties, the genetic composition of the region began to resemble that of modern Shandong populations. Our genetic findings suggest that the middle Yellow River Basin farmers played a role in shaping the genetic affinity of neighboring populations in northern China during the Middle to Late Neolithic period. Additionally, our findings indicate that the genetic diversity in the Shandong region during the Zhou Dynasty may be linked with their complex ethnicities.

Genetic admixture predictors of fetal alcohol spectrum disorders (FASD) in a South African population

Ancestrally admixed populations are underrepresented in genetic studies of complex diseases, which are still dominated by European-descent populations. This is relevant not only from a representation standpoint but also because of admixed populations’ unique features, including being enriched for rare variants, for which effect sizes are disproportionately larger than common polymorphisms. Furthermore, results from these populations may be generalizable to other populations. The South African Cape Coloured (SACC) population is genetically admixed and has one of the highest prevalences of fetal alcohol spectrum disorders (FASD) worldwide. We profiled its admixture and examined associations between ancestry profiles and FASD outcomes using two longitudinal birth cohorts (N=308 mothers, 280 children) designed to examine effects of prenatal alcohol exposure on development. Participants were genotyped via MEGAex array to capture common and rare variants. Rare variants were overrepresented in our SACC cohorts, with numerous polymorphisms being monomorphic in other reference populations (e.g., ∼30,000 and ∼ 221,000 variants in gnomAD European and Asian populations, respectively). The cohorts showed global African (51 %; Bantu and San); European (26 %; Northern/Western); South Asian (18 %); and East Asian (5 %; largely Southern regions) ancestries. The cohorts exhibited high rates of homozygosity (6 %), with regions of homozygosity harboring more deleterious variants when lying within African local-ancestry genomic segments. Both maternal and child ancestry profiles were associated with higher FASD risk, and maternal and child ancestry-by-prenatal alcohol exposure interaction effects were seen on child cognition. Our findings indicate that the SACC population may be a valuable asset to identify novel disease-associated genetic loci for FASD and other diseases.

Fitness consequences of population bottlenecks in an invasive blowfly.

Invasive species often undergo demographic bottlenecks that cause a decrease in genetic diversity and associated reductions in population fitness. Despite this, they manage to thrive in novel environments. Investigating the effects of inbreeding and genetic bottlenecks on population fitness for invasive species is, therefore, key to understanding how they may survive in new environments. We used the blowfly Calliphora vicina (Sciences, Mathématiques et Physique, 1830, 2, 1), which is native to Europe and was introduced to Australia and New Zealand, to examine the effects of genetic diversity on population fitness. We first collected 59 samples from 15 populations across New Zealand and one in Australia, and used 20,501 biallelic SNPs to investigate population genomic diversity, structure and admixture. We then explored the impacts of repeated experimental bottlenecks on population fitness by creating inbred and outbred lines of C. vicina and measuring a variety of fitness traits. In wild-caught samples, we found low overall genetic diversity, signals of genetic admixture and limited (<3%) genetic differentiation between North and South Island populations, with genetic links between the South Island and Australia. Following experimental bottlenecks, we found significant reductions in fitness for inbred lines. However, fitness effects were not felt equally across all phenotypic traits. Moreover, they were not enough to cause population collapse in any experimental line, suggesting that C. vicina (when under relaxed selection, as in laboratory settings) may be able to compensate for population bottlenecks even when highly inbred. Our results demonstrate the value of a tractable experimental system for investigating processes that may facilitate or hamper biological invasion.

Genomic, morphological and physiological data support fast ecotypic differentiation and incipient speciation in an alpine diving beetle.

An intricate interplay between evolutionary and demographic processes has frequently resulted in complex patterns of genetic and phenotypic diversity in alpine lineages, posing serious challenges to species delimitation and biodiversity conservation planning. Here we integrate genomic data, geometric morphometric analyses and thermal tolerance experiments to explore the role of Pleistocene climatic changes and adaptation to alpine environments on patterns of genomic and phenotypic variation in diving beetles from the taxonomically complex Agabus bipustulatus species group. Genetic structure and phylogenomic analyses revealed the presence of three geographically cohesive lineages, two representing trans-Palearctic and Iberian populations of the elevation-generalist A. bipustulatus and another corresponding to the strictly-alpine A. nevadensis, a narrow-range endemic taxon from the Sierra Nevada mountain range in southeastern Iberia. The best-supported model of lineage divergence, along with the existence of pervasive genetic introgression and admixture in secondary contact zones, is consistent with a scenario of population isolation and connectivity linked to Quaternary climatic oscillations. Our results suggest that A. nevadensis is an alpine ecotype of A. bipustulatus, whose genotypic, morphological and physiological differentiation likely resulted from an interplay between population isolation and local altitudinal adaptation. Remarkably, within the Iberian Peninsula, such ecotypic differentiation is unique to Sierra Nevada populations and has not been replicated in other alpine populations of A. bipustulatus. Collectively, our study supports fast ecotypic differentiation and incipient speciation processes within the study complex and points to Pleistocene glaciations and local adaptation along elevational gradients as key drivers of biodiversity generation in alpine environments.

Evaluation of genetic diversity among olive trees (Olea europaea L.) from Jordan.

This study aimed to identify and evaluate the genetic diversity of olive trees in Jordan, a country located in the eastern Mediterranean, where olive domestication originated. For this purpose, a total of 386 olive trees were analyzed, including 338 collected from two surveys (JOCC-1 and JOCC-2) across seven regions, and 48 selected accessions from the Olive Germplasm Bank of Jordan (JGBOC). These trees underwent comprehensive phenotypic and molecular characterization using different tools. Significant differences in morphological traits were detected among tested regions using the Chi-square test. Principal components analysis revealed that fruit color change and growth habit as the most discriminating traits, segregating the trees into two groups, with the first group including the Kanabisi cultivar and the second group including the Kfari Baladi cultivar. Utilizing Kompetitive Allele Specific PCR assay, two sets of informative SNPs were used for the genetic diversity analysis. Cladograms were constructed using the maximum likelihood method, revealing a consistent pattern where two clades containing identical genotypes were observed to cluster with the Kfari Baladi or Kanabisi. In addition, the SNP data was used to perform a comparative analysis with the Worldwide Olive Germplasm Bank of Córdoba, which revealed 73 unreported olive genotypes from Jordan. Genetic structure analyses using Discriminant Analysis of Principal Components (DAPC) identified four clusters with distinctive patterns of relatedness among 149 unique accessions, including 52 olive accessions from various Mediterranean countries (IOCC-3). ADMIXTURE analysis revealed four genetic clusters, consistent with the clustering observed in DAPC and cladogram analysis, indicating a high level of genetic admixture among Jordanian olive germplasm. In conclusion, the results show that olive trees in Jordan are highly diverse, providing valuable information for future conservation and management plans.

Global and Local Ancestry and its Importance: A Review.

The fastest way to significantly change the composition of a population is through admixture, an evolutionary mechanism. In animal breeding history, genetic admixture has provided both short-term and long-term advantages by utilizing the phenomenon of complementarity and heterosis in several traits and genetic diversity, respectively. The traditional method of admixture analysis by pedigree records has now been replaced greatly by genome-wide marker data that enables more precise estimations. Among these markers, SNPs have been the popular choice since they are cost-effective, not so laborious, and automation of genotyping is easy. Certain markers can suggest the possibility of a population's origin from a sample of DNA where the source individual is unknown or unwilling to disclose their lineage, which are called Ancestry-Informative Markers (AIMs). Revealing admixture level at the locus-specific level is termed as local ancestry and can be exploited to identify signs of recent selective response and can account for genetic drift. Considering the importance of genetic admixture and local ancestry, in this mini-review, both concepts are illustrated, encompassing basics, their estimation/identification methods, tools/software used and their applications.

Multi-generational benefits of genetic rescue

Genetic rescue—an increase in population fitness following the introduction of new alleles—has been proven to ameliorate inbreeding depression in small, isolated populations, yet is rarely applied as a conservation tool. A lingering question regarding genetic rescue in wildlife conservation is how long beneficial effects persist in admixed populations. Using data collected over 40 years from 1192 endangered Florida panthers (Puma concolor coryi) across nine generations, we show that the experimental genetic rescue implemented in 1995—via the release of eight female pumas from Texas—alleviated morphological, genetic, and demographic correlates of inbreeding depression, subsequently preventing extirpation of the population. We present unequivocal evidence, for the first time in any terrestrial vertebrate, that genetic and phenotypic benefits of genetic rescue remain in this population after five generations of admixture, which helped increase panther abundance (> fivefold) and genetic effective population size (> 20-fold). Additionally, even with extensive admixture, microsatellite allele frequencies in the population continue to support the distinctness of Florida panthers from other North American puma populations, including Texas. Although threats including habitat loss, human-wildlife conflict, and infectious diseases are challenges to many imperiled populations, our results suggest genetic rescue can serve as an effective, multi-generational tool for conservation of small, isolated populations facing extinction from inbreeding.

Novel loci linked to serum lipid traits are identified in a genome-wide association study of a highly admixed Brazilian population - the 2015 ISA Nutrition

BackgroundCardiovascular diseases (CVDs) comprise major causes of death worldwide, leading to extensive burden on populations and societies. Alterations in normal lipid profiles, i.e., dyslipidemia, comprise important risk factors for CVDs. However, there is lack of comprehensive evidence on the genetic contribution to dyslipidemia in highly admixed populations. The identification of single nucleotide polymorphisms (SNPs) linked to blood lipid traits in the Brazilian population was based on genome-wide associations using data from the São Paulo Health Survey with Focus on Nutrition (ISA-Nutrition).MethodsA total of 667 unrelated individuals had genetic information on 330,656 SNPs available, and were genotyped with Axiom™ 2.0 Precision Medicine Research Array. Genetic associations were tested at the 10− 5 significance level for the following phenotypes: low-density lipoprotein cholesterol (LDL-c), very low-density lipoprotein cholesterol (VLDL-c), high-density lipoprotein cholesterol (HDL-c), HDL-c/LDL-c ratio, triglycerides (TGL), total cholesterol, and non-HDL-c.ResultsThere were 19 significantly different SNPs associated with lipid traits, the majority of which corresponding to intron variants, especially in the genes FAM81A, ZFHX3, PTPRD, and POMC. Three variants (rs1562012, rs16972039, and rs73401081) and two variants (rs8025871 and rs2161683) were associated with two and three phenotypes, respectively. Among the subtypes, non-HDL-c had the highest proportion of associated variants.ConclusionsThe results of the present genome-wide association study offer new insights into the genetic structure underlying lipid traits in underrepresented populations with high ancestry admixture. The associations were robust across multiple lipid phenotypes, and some of the phenotypes were associated with two or three variants. In addition, some variants were present in genes that encode ncRNAs, raising important questions regarding their role in lipid metabolism.

Analysis of sex-biased gene expression in a Eurasian admixed population.

Sex-biased gene expression differs across human populations; however, the underlying genetic basis and molecular mechanisms remain largely unknown. Here, we explore the influence of ancestry on sex differences in the human transcriptome and its genetic effects on a Eurasian admixed population: Uyghurs living in Xinjiang (XJU), by analyzing whole-genome sequencing data and transcriptome data of 90 XJU and 40 unrelated Han Chinese individuals. We identified 302 sex-biased expressed genes and 174 sex-biased cis-expression quantitative loci (sb-cis-eQTLs) in XJU, which were enriched in innate immune-related functions, indicating sex differences in immunity. Notably, approximately one-quarter of the sb-cis-eQTLs showed a strong correlation with ancestry composition; i.e. populations of similar ancestry tended to show similar patterns of sex-biased gene expression. Our analysis further suggested that genetic admixture induced a moderate degree of sex-biased gene expression. Interestingly, analysis of chromosome interactions revealed that the X chromosome acted on autosomal immunity-associated genes, partially explaining the sex-biased phenotypic differences. Our work extends the knowledge of sex-biased gene expression from the perspective of genetic admixture and bridges the gap in the exploration of sex-biased phenotypes shaped by autosome and X-chromosome interactions. Notably, we demonstrated that sex chromosomes cannot fully explain sex differentiation in immune-related phenotypes.

Waves of Colonization and Gene Flow in a Great Speciator.

Secondary contact between previously allopatric lineages offers a test of reproductive isolating mechanisms that may have accrued in isolation. Such instances of contact can produce stable hybrid zones-where reproductive isolation can further develop via reinforcement or phenotypic displacement-or result in the lineages merging. Ongoing secondary contact is most visible in continental systems, where steady input from parental taxa can occur readily. In oceanic island systems, however, secondary contact between closely related species of birds is relatively rare. When observed on sufficiently small islands, relative to population size, secondary contact likely represents a recent phenomenon. Here, we examine the dynamics of a group of birds whose apparent widespread hybridization influenced Ernst Mayr's foundational work on allopatric speciation: the whistlers of Fiji (Aves: Pachycephala). We demonstrate two clear instances of secondary contact within the Fijian archipelago, one resulting in a hybrid zone on a larger island, and the other resulting in a wholly admixed population on a smaller, adjacent island. We leveraged low genome-wide divergence in the hybrid zone to pinpoint a single genomic region associated with observed phenotypic differences. We use genomic data to present a new hypothesis that emphasizes rapid plumage evolution and post-divergence gene flow.

Genetic admixture drives climate adaptation in the bank vole

Genetic admixture introduces new variants at relatively high frequencies, potentially aiding rapid responses to environmental changes. Here, we evaluate its role in adaptive variation related to climatic conditions in bank voles (Clethrionomys glareolus) in Britain, using whole-genome data. Our results reveal loci showing excess ancestry from one of the two postglacial colonist populations inconsistent with overall admixture patterns. Notably, loci associated with climate adaptation exhibit disproportionate amounts of excess ancestry, highlighting the impact of admixture between colonist populations on local adaptation. The results suggest strong and localized selection on climate-adaptive loci, as indicated by steep clines and/or shifted cline centres, during population replacement. A subset, including a haemoglobin gene, is associated with oxidative stress responses, underscoring a role of oxidative stress in local adaptation. Our study highlights the important contribution of admixture during secondary contact between populations from distinct climatic refugia enriching adaptive diversity. Understanding these dynamics is crucial for predicting future adaptive capacity to anthropogenic climate change.

Phylogeography and genetic structure of Papaver bracteatum populations in Iran based on genotyping-by-sequencing (GBS)

Papaver bracteatum, known for its high thebaine content and absence of morphine, has emerged as a promising alternative to opium poppy for codeine production. In this study, our objective was to create a diverse panel representing the natural variation of this species in Iran. To achieve this, we employed genotyping-by-sequencing to obtain genome-wide distributed single-nucleotide polymorphisms (SNPs) for phylogeographic analysis, population structure assessment, and evaluation of genetic diversity within P. bracteatum populations. A total of 244 P. bracteatum individuals from 13 distinct populations formed seven genetic groups, along with one highly admixed population. We observed a clear split between the populations inhabiting the Alborz Mts. in the east and Zagros Mts. in the west. In between these mountain ranges, the population of Kachal Mangan exhibited a high degree of genetic admixture between both genetic groups. At or after the end of the last glacial maximum, when climate conditions rapidly changed, all P. bracteatum populations experienced a strong demographic bottleneck reducing the already small effective population sizes further before they increased to their recent strengths. Our results suggest that the ongoing climate change together with human pressure on the species’ habitats and limited seed-dispersal ability are potential factors contributing today to rising genetic isolation of P. bracteatum populations. Our results provide genetic data that can be used for conservation measures to safeguard the species’ genetic diversity as a resource for future breeding approaches in this medicinally important species.

Unlocking Nile tilapia (Oreochromis niloticus Linn., 1758) selective breeding programmes in Uganda through geographical genetic structure mapping

AbstractNile tilapia (Oreochromis niloticus), native to Africa and the Levant, is an important species for both aquaculture and capture fisheries. Despite these attributes, Nile tilapia has been negatively impacted by anthropogenic activities ranging from overfishing and habitat destruction to translocations. These human‐mediated activities have threatened the genetic evolutionary integrity of native populations of Nile tilapia and congeneric species through admixture, demographic bottlenecks and introgressive hybridization. In this context, the genetic contrast between farmed/bred strains and wild Nile tilapia populations in the major lakes of Uganda remains understudied. Understanding the genetic structure of Nile tilapia populations in the major water bodies of Uganda (lakes Victoria, Kyoga, Edward, George, Albert and Nile River) is a key resource to guide selective breeding programmes, thus minimizing the effects of maladaptation under both aquaculture and natural stocks. Although the population genetics of Nile tilapia in Uganda's major lakes have been studied, this was based on limited sampling scope, especially in the wild, and the key information on the species could have been overlooked. We fill this knowledge gap by genotyping 756 Nile tilapia individuals from multiple populations for each major water body of Uganda using a panel of 34 microsatellite loci based on the microsatellite genotyping‐by‐sequencing (SSR‐GBS) technique. The results indicate two discrete gene pools/stocks: the Edward‐George system and the Albert‐Kyoga system‐Victoria. Evidence of loss of genetic diversity and admixture of some Nile tilapia stocks was found, most likely resulting from anthropogenic perturbations. This study contributes useful information key for understanding the potential Nile tilapia broodstock sources for selective breeding programmes, aimed at improving aquaculture production in Uganda.

Genetic Ancestry and Self-Reported "Skin Color/Race" in the Urban Admixed Population of São Paulo City, Brazil.

Epidemiological studies frequently classify groups based on phenotypes like self-reported skin color/race, which inaccurately represent genetic ancestry and may lead to misclassification, particularly among individuals of multiracial backgrounds. This study aimed to characterize both global and local genome-wide genetic ancestries and to assess their relationship with self-reported skin color/race in an admixed population of Sao Paulo city. We analyzed 226,346 single-nucleotide polymorphisms from 841 individuals participating in the population-based ISA-Nutrition study. Our findings confirmed the admixed nature of the population, demonstrating substantial European, significant Sub-Saharan African, and minor Native American ancestries, irrespective of skin color. A correlation was observed between global genetic ancestry and self-reported color-race, which was more evident in the extreme proportions of African and European ancestries. Individuals with higher African ancestry tended to identify as Black, those with higher European ancestry tended to identify as White, and individuals with higher Native American ancestry were more likely to self-identify as Mixed, a group with diverse ancestral compositions. However, at the individual level, this correlation was notably weak, and no deviations were observed for specific regions throughout the individual's genome. Our findings emphasize the significance of accurately defining and thoroughly analyzing race and ancestry, especially within admixed populations.

Historical and contemporary processes driving the origin and structure of an admixed population within a contact zone between subspecies of a north temperate diadromous fish.

Hybridization between divergent lineages can result in losses of distinct evolutionary taxa. Alternatively, hybridization can lead to increased genetic variability that may fuel local adaptation and the generation of novel traits and/or taxa. Here, we examined single-nucleotide polymorphisms generated using genotyping-by-sequencing in a population of Dolly Varden char (Pisces: Salmonidae) that is highly admixed within a contact zone between two subspecies (Salvelinus malma malma, Northern Dolly Varden [NDV] and S. m. lordi, Southern Dolly Varden [SDV]) in southwestern Alaska to assess the spatial distribution of hybrids and to test hypotheses on the origin of the admixed population. Ancestry analysis revealed that this admixed population is composed of advanced generation hybrids between NDV and SDV or advanced backcrosses to SDV; no F1 hybrids were detected. Coalescent-based demographic modelling supported the origin of this population about 55,000 years ago by secondary contact between NDV and SDV with low levels of contemporary gene flow. Ancestry in NDV and SDV varies within the watershed and ancestry in NDV was positively associated with distance upstream from the sea, contingent on habitat-type sampled, and negatively associated with the number of migrations that individual fish made to the sea. Our results suggest that divergence between subspecies over hundreds of thousands of years may not be associated with significant reproductive isolation, but that elevated diversity owing to hybridization may have contributed to adaptive divergence in habitat use and life history.

Population expansion, larger, and more homogeneous native American ancestry among Mexican mestizo populations based on 10 X-chromosome STR loci (X-STR decaplex system).

To evaluate the genetic diversity, admixture, genetic relationships, and sex-biased demographic processes in Mexican Mestizo (admixed) populations based on 10 X-chromosome STRs (X-STRs). We analyzed the X-STRs Decaplex system in 104 Mexican Native Americans to obtain the ancestral reference needed to complete the demographic analyses above mentioned. We included reported Iberian and Latin American (admixed) populations from Central and South America, as well as datasets from Mexican Mestizos based on Y-linked STRs (Y-STRs), autosomal STRs (A-STRs), and mtDNA. Higher X-linked Native American ancestry was observed among Latin American populations regarding that reported from A-STRs and Y-STRs. The interpopulation differentiation based on ancestry among Mexican Mestizos diminished according to the inheritance pattern: Y-STRs (highest), A-STRs, X-STRs, and mtDNA (lowest). This finding is related to the peculiar admixture process that occurred during and after the Spanish Conquest of Mexico (and most of Latin America), involving a large number of Spanish men (Y-chromosomes) with a lesser proportion of X-chromosomes than autosomes; besides to the limited number of Spanish women (XX) arrived in the Americas in subsequent and shorter periods. Population expansion was detected in Mexican Mestizos from all the country, except those from the southeast region characterized by elevated indigenous ancestry, marginalization, and poorness. Population growth was detected in most Mexican Mestizos, besides more homogeneous and larger Native American ancestry based on X-linked inheritance than that based on autosomal STRs and Y-STRs.