Levels Of Admixture Research Articles

The Genetic Architecture of Parkinson Disease in Spain: Characterizing Population-Specific Risk, Differential Haplotype Structures, and Providing Etiologic Insight.

The Iberian Peninsula stands out as having variable levels of population admixture and isolation, making Spain an interesting setting for studying the genetic architecture of neurodegenerative diseases. To perform the largest PD genome-wide association study restricted to a single country. We performed a GWAS for both risk of PD and age at onset in 7,849 Spanish individuals. Further analyses included population-specific risk haplotype assessments, polygenic risk scoring through machine learning, Mendelian randomization of expression, and methylation data to gain insight into disease-associated loci, heritability estimates, genetic correlations, and burden analyses. We identified a novel population-specific genome-wide association study signal at PARK2 associated with age at onset, which was likely dependent on the c.155delA mutation. We replicated four genome-wide independent signals associated with PD risk, including SNCA, LRRK2, KANSL1/MAPT, and HLA-DQB1. A significant trend for smaller risk haplotypes at known loci was found compared to similar studies of non-Spanish origin. Seventeen PD-related genes showed functional consequence by two-sample Mendelian randomization in expression and methylation data sets. Long runs of homozygosity at 28 known genes/loci were found to be enriched in cases versus controls. Our data demonstrate the utility of the Spanish risk haplotype substructure for future fine-mapping efforts, showing how leveraging unique and diverse population histories can benefit genetic studies of complex diseases. The present study points to PARK2 as a major hallmark of PD etiology in Spain. © 2019 International Parkinson and Movement Disorder Society.

Impact of merging commercial breeding lines on the genetic diversity of Landrace pigs

BackgroundThe pig breeding industry has undergone a large number of mergers in the past decades. Various commercial lines were merged or discontinued, which is expected to reduce the genetic diversity of the pig species. The objective of the current study was to investigate the genetic diversity of different former Dutch Landrace breeding lines and quantify their relationship with the current Dutch Landrace breed that originated from these lines.ResultsPrincipal component analysis clearly divided the former Landrace lines into two main clusters, which are represented by Norwegian/Finnish Landrace lines and Dutch Landrace lines. Structure analysis revealed that each of the lines that are present in the Dutch Gene bank has a unique genetic identity. The current Dutch Landrace breed shows a high level of admixture and is closely related to the six former lines. The Dumeco N-line, which is conserved in the Dutch Gene bank, is poorly represented in the current Dutch Landrace. All seven lines (the six former and the current line) contribute almost equally to the genetic diversity of the Dutch Landrace breed. As expected, the current Dutch Landrace breed comprises only a small proportion of unique genetic diversity that was not present in the other lines. The genetic diversity level, as measured by Eding’s core set method, was equal to 0.89 for the current Dutch Landrace breed, whereas total genetic diversity across the seven lines, measured by the same method, was equal to 0.99.ConclusionsThe current Dutch Landrace breed shows a high level of admixture and is closely related to the six former Dutch Landrace lines. Merging of commercial Landrace lines has reduced the genetic diversity of the Landrace population in the Netherlands, although a large proportion of the original variation is maintained. Thus, our recommendation is to conserve breeding lines in a gene bank before they are merged.

Oh, what a tangled web we weave

Oh, what a tangled web we weave

Eastern Anatolian apples with a unique population structure are genetically different from Anatolian apples

The origin of the apple is known to be the Transcaucasian region. Eastern Anatolia, which is located on the migration routes from Asia to Europe, has a rich and an uncharacterized apple germplasm and the characterization of apple genetic sources from this region is important for both evolutionary studies and apple breeding. In this study, 94 M. domestica accessions originated from seven diverse regions within Eastern Anatolia were studied using 16 SSR (simple sequence repeat) loci. SSR markers we used produced high allele numbers in all loci and CH02d11 (PI: 0.059) with 18 alleles was the most informative locus. In addition, 14 identical accession groups were identified. Most likely due to self-incompatibility, relatively high levels of heterozygosity (Ho: 0.696) was found for Eastern Anatolia apples. Structure Harvester analyses of East Anatolian apple accessions showed that although each group seems to be somewhat distinct, some levels of admixture with other populations might also exist. Due to a significant gene flow between all pairs of seven apple populations, a limited (low) differentiation was found between the populations. Comparisons using 16 common SSR loci revealed that Eastern Anatolia accessions were genetically different from Anatolian accessions. In addition, based on FCA, and Nei’s genetic distance analyses, Eastern Anatolian apples were found to be genetically different from the commercial apple cultivars Golden Delicious and Florina. Our results suggesting that Eastern Anatolia apple populations have a unique structure will be useful for future genetic and evolutionary studies on apples.

European Roma groups show complex West Eurasian admixture footprints and a common South Asian genetic origin

The Roma population is the largest transnational ethnic minority in Europe, characterized by a linguistic, cultural and historical heterogeneity. Comparative linguistics and genetic studies have placed the origin of European Roma in the Northwest of India. After their migration across Persia, they entered into the Balkan Peninsula, from where they spread into Europe, arriving in the Iberian Peninsula in the 15th century. Their particular demographic history has genetic implications linked to rare and common diseases. However, the South Asian source of the proto-Roma remains still untargeted and the West Eurasian Roma component has not been yet deeply characterized. Here, in order to describe both the South Asian and West Eurasian ancestries, we analyze previously published genome-wide data of 152 European Roma and 34 new Iberian Roma samples at a fine-scale and haplotype-based level, with special focus on the Iberian Roma genetic substructure. Our results suggest that the putative origin of the proto-Roma involves a Punjabi group with low levels of West Eurasian ancestry. In addition, we have identified a complex West Eurasian component (around 65%) in the Roma, as a result of the admixture events occurred with non-proto-Roma populations between 1270–1580. Particularly, we have detected the Balkan genetic footprint in all European Roma, and the Baltic and Iberian components in the Northern and Western Roma groups, respectively. Finally, our results show genetic substructure within the Iberian Roma, with different levels of West Eurasian admixture, as a result of the complex historical events occurred in the Peninsula.

Revelation of genomic breed composition in a crossbred cattle of India with the help of Bovine50K BeadChip

The aim of the present study was to assess the population structure and admixture levels in the Vrindavani composite population in India by using Bovine50KSNP BeadChip data. Genotypic data were generated for randomly selected animals (n = 72) of Vrindavani population and the data for parental breeds i.e., Hariana (n = 10), Holstein-Friesian (n = 63), Jersey (n = 28) and Brown Swiss (n = 22) were retrieved from a public repository. The indices of population structure were calculated using PLINK software and R-program. The merged dataset was analysed for assessing admixture levels and population stratification using three different approaches i.e., principal component analysis (PCA), multi-dimensional scaling (MDS) approach and the model-based approach in STRUCTURE software. The average minor allele frequency (MAF) value for Vrindavani population was estimated to be 0.235. Vrindavani population was found to possess an average ancestry of 39.5, 22.9, 26.9, and 10.7% inheritance levels from Holstein Friesian, Jersey, Hariana and Brown Swiss cattle breeds, respectively.

High levels of recent wolf × dog introgressive hybridization in agricultural landscapes of central Italy

Representing a form of anthropogenic hybridization, wolf–dog interbreeding may potentially compromise the ecological and evolutionary traits of local wolf populations and corrode social tolerance towards wolves. However, estimates of the extent of wolf–dog hybridization in wolf populations are scarce, especially at a multi-pack scale and in human-dominated landscapes. Using non-invasive (n = 215) and invasive (n = 25) samples of wolf-like canids collected in the Province of Grosseto (central Italy, 2012–2014), we assessed the extent of wolf–dog hybridization based on multi-locus genotypes (16 and 49 loci for non-invasive and invasive samples, respectively) and Bayesian clustering techniques. Based on a total of 72 genotypes, the minimum proportion of admixed individuals in our sample was 30.6%, comprising 8 out of the 13 surveyed packs; however, by correcting for the proportion of admixed individuals undetected using the 16-loci compared with the 49-loci marker set (26.7%), we suspect the rate of recent admixture could be closer to 50%. While we did not detect any F1 hybrid, four admixed individuals had a non-negligible probability of being first-generation backcrosses, one of which likely derived from a backcross of a F1 hybrid into the dog population. Complementary genetic markers (i.e., Y-haplotype and K-locus) or anomalous morphological traits further indicated widespread occurrence of admixed individuals of older generations of backcross. This high level of admixture raises serious wolf conservation concerns and exemplifies the expected dynamics of wolf–dog hybridization if left unmanaged in human-dominated landscapes. The implications of our findings need to be urgently upscaled for the implementation of management interventions that cannot be procrastinated any longer at the regional and national scale.

Genomic approaches to identify hybrids and estimate admixture times in European wildcat populations

The survival of indigenous European wildcat (Felis silvestris silvestris) populations can be locally threatened by introgressive hybridization with free-ranging domestic cats. Identifying pure wildcats and investigating the ancestry of admixed individuals becomes thus a conservation priority. We analyzed 63k cat Single Nucleotide Polymorphisms (SNPs) with multivariate, Bayesian and gene-search tools to better evaluate admixture levels between domestic and wild cats collected in Europe, timing and ancestry proportions of their hybrids and backcrosses, and track the origin (wild or domestic) of the genomic blocks carried by admixed cats, also looking for possible deviations from neutrality in their inheritance patterns. Small domestic ancestry blocks were detected in the genomes of most admixed cats, which likely originated from hybridization events occurring from 6 to 22 generations in the past. We identified about 1,900 outlier coding genes with excess of wild or domestic ancestry compared to random expectations in the admixed individuals. More than 600 outlier genes were significantly enriched for Gene Ontology (GO) categories mainly related to social behavior, functional and metabolic adaptive processes (wild-like genes), involved in cognition and neural crest development (domestic-like genes), or associated with immune system functions and lipid metabolism (parental-like genes). These kinds of genomic ancestry analyses could be reliably applied to unravel the admixture dynamics in European wildcats, as well as in other hybridizing populations, in order to design more efficient conservation plans.

Consequences of habitat fragmentation on genetic diversity and structure of Salix alba L. populations in two major river systems of Turkey

Salix alba L. (white willow) is an indicator species of a healthy riparian ecosystem with great renewable energy potential in Turkey though habitats of the species in many river ecosystems are highly degraded or fragmented. Impacts of this degradation of river ecosystems on the magnitude and pattern of genetic diversity are not known. This study was aimed at assessing the genetic structure of S. alba populations in two highly degraded and fragmented river systems (the Goksu and Kizilirmak rivers) in Turkey with the use of 20 nuclear simple sequence repeat (SSR) loci. Fifteen of them were used for the first time in this study. Out of the 20 SSR loci, 10 loci significantly deviated from the Hardy-Weinberg equilibrium frequencies and five of them contributed greatly to the differentiation of populations. Generally, high levels of genetic diversity were found in populations of both Goksu and Kizilirmak river systems and moderate genetic differentiation (FST = 0.07) between the river systems. On the contrary to expectations, genetic diversity was higher in middle populations of the rivers (Ho = 0.67 of GRMID (Goksu river middle population), Ho = 0.68 in KRMID1 (Kizilirmak river middle population 1), and 0.65 in KRMID2 (Kizilirmak river middle population 2)) than in downstream populations (Ho = 0.65 in GRDOWN (Goksu river downstream population), Ho = 0.62 in KRDOWN1, 2 (Kizilirmak downstream populations 1, 2)). These could be due to experienced past bottlenecks, extensive vegetative material movements, and habitat fragmentation by constructed dams in the natural ecosystems of the two river systems. The genetic structure results revealed that the white willow populations in the two different river systems may have evolved from two different founder populations. A low level of genetic admixture between the river systems but high admixture within the river systems were observed due to extensive human-mediated vegetative material movements. The current study has provided valuable genetic data and information that could contribute insights to efficient conservation, management, utilization, and breeding of genetic resources of the species.

A Statewide Evaluation of Florida Bass Genetic Introgression in Tennessee

AbstractThe Largemouth Bass (LMB) Micropterus salmoides is one of the most popular freshwater sport fish in the United States, and managers in southeastern states have stocked its subspecies, the Florida Bass (FLB) M. salmoides floridanus, outside of the subspecies’ natural range to increase the size structure of existing LMB populations. In Tennessee, fisheries for LMB are concentrated in reservoirs of the Cumberland and Tennessee River systems; however, FLB stockings have to date been restricted to two reservoirs of the Tennessee River and have varied significantly in extent and duration. We quantified levels of genetic admixture between FLB and LMB by using 38 species‐diagnostic single‐nucleotide polymorphisms for 979 fish sampled from 14 reservoirs within the Cumberland and Tennessee River systems. We tested for differences in genetic admixture across river systems and evaluated the relative importance of fish stockings in explaining observed levels of genetic admixture. Levels of admixture and associated variation were higher in Tennessee River reservoirs (average percentage of FLB alleles: range = 6.3–30.4%) than in Cumberland River reservoirs (range = 5.7–13.4%), but admixture was not solely related to stocking rates. The highest levels of FLB introgression were detected in Chickamauga Reservoir, the most extensively stocked reservoir in the state. Linear models identified fish stocked as a significant overall predictor of admixture, but we also observed stocked and unstocked reservoirs with similar levels of admixture, suggesting that factors other than stocking influence population genetics. Our statewide assessment of reservoir‐level patterns of hybridization among black bass was performed prior to the recent expansion of FLB stocking efforts in Tennessee and thus represents a baseline for evaluation of future stocking.

The population genetic structure approach adds new insights into the evolution of plant LTR retrotransposon lineages.

Long terminal repeat retrotransposons (LTR-RTs) in plant genomes differ in abundance, structure and genomic distribution, reflecting the large number of evolutionary lineages. Elements within lineages can be considered populations, in which each element is an individual in its genomic environment. In this way, it would be reasonable to apply microevolutionary analyses to understand transposable element (TE) evolution, such as those used to study the genetic structure of natural populations. Here, we applied a Bayesian method to infer genetic structure of populations together with classical phylogenetic and dating tools to analyze LTR-RT evolution using the monocot Setaria italica as a model species. In contrast to a phylogeny, the Bayesian clusterization method identifies populations by assigning individuals to one or more clusters according to the most probabilistic scenario of admixture, based on genetic diversity patterns. In this work, each LTR-RT insertion was considered to be one individual and each LTR-RT lineage was considered to be a single species. Nine evolutionary lineages of LTR-RTs were identified in the S. italica genome that had different genetic structures with variable numbers of clusters and levels of admixture. Comprehensive analysis of the phylogenetic, clusterization and time of insertion data allowed us to hypothesize that admixed elements represent sequences that harbor ancestral polymorphic sequence signatures. In conclusion, application of microevolutionary concepts in genome evolution studies is suitable as a complementary approach to phylogenetic analyses to address the evolutionary history and functional features of TEs.

Admixture analyses and phylogeographic relationships reveal complete genetic distinctiveness of Polish farm and wild red foxes (Vulpes vulpes) and the North American origin of farm-bred individuals.

A number of studies showed that many mtDNA haplotypes were shared among contemporary farm red foxes bred on different continents and the historical wild red foxes of North American origin. Therefore, in this study, the population genetic structure and phylogeographic relationships of Polish red foxes kept on fur farms and their wild conspecifics were investigated to assess the ancestry of the farm red foxes in Poland. A total of 330 tissue samples (200 from farm foxes and 130 from wild foxes) were used for the genetic analyses. Thirty microsatellite loci and two regions of mtDNA were used to assess the level of admixture between farm- and wild red foxes, to construct haplotype networks and create a phylogenetic tree. The genetic structure analysis clearly indicated two genetic clusters as being the most probable number of genetically distinct populations. The fixation index revealed a significant genetic distance between the farm- and wild red fox populations (FST =0.27, p<0.05). Haplotype networks based on frequencies showing relationships between concatenated haplotypes of Polish farm- and wild red foxes and the constructed phylogenetic tree clearly indicated two genetically distinct groups. The results of this study provide strong evidence confirming the North American origin of red foxes bred on Polish farms and the genetic distinctiveness of both studied populations.

Possible European Origin of Circulating Varicella Zoster Virus Strains.

Varicella zoster virus (VZV) is the causative agent of chickenpox and shingles. The geographic distribution of VZV clades was taken as evidence that VZV migrated out of Africa with human populations. We show that extant VZV strains most likely originated in Europe and not in Africa. Europe was also identified as the ancestral location for most internal nodes of the VZV phylogeny, including the ancestor of clade 5 strains. We also show that strains from clades 1, 2, 3, and 5 derived a major proportion of their ancestry from each of 4 ancestral populations. Conversely, viruses from other clades displayed variable levels of admixture. Some low-level admixture was also observed for clade 5 genomes, but only for non-African viruses. This pattern indicates that the clade 5 VZV strains do not represent recent introductions from Africa due to migratory fluxes. These data have also relevance for the definition and classification of VZV clades.

Population genetic structure and demographic history of Spodoptera frugiperda (Lepidoptera: Noctuidae): implications for insect resistance management programs.

Spodoptera frugiperda is a destructive pest that often imposes difficult management due to its high polyphagy and rapid insecticide resistance evolution. Knowledge of species diversification, population structure, and host preference can aid efforts to manage pest populations. Here, we investigated the patterns of hybridization, genetic structure, and gene flow in S. frugiperda populations, discussing how we can apply this knowledge to insect resistance management programs in South America. The corn-strain CS-h2 of S. frugiperda was the most frequent haplotype in all sampled populations. Spodoptera frugiperda populations are experiencing demographic expansion, and the ecoregions partially explain the genetic structure and not strains. We did not find a correlation between gene flow and susceptibility levels to flubendiamide and lufenuron insecticides, but populations with high LC50 sent a great number of migrants to all other locations, maintaining resistance alleles in the geographic range. High levels of population admixture, including between corn- and rice-strains, were found in sampled populations. We showed that S. frugiperda immigrants will not necessarily cause an increase in LC50 upon arrival in a new location but will assure the constant presence of resistance alleles in the area. Increases in LC50 largely depend on the local pesticide management adopted in the areas. Our results indicate that pesticide resistance management must be adopted on a local or small regional scale. © 2019 Society of Chemical Industry.

Population structure of Betula albosinensis and Betula platyphylla: evidence for hybridization and a cryptic lineage.

Background and AimsDifferences in local abundance and ploidy level are predicted to impact the direction of introgression between species. Here, we tested these hypotheses on populations of Betula albosinensis (red birch) and Betula platyphylla (white birch) which were thought to differ in ploidy level, the former being tetraploid and the latter diploid.MethodsWe sampled 391 birch individuals from nine localities in China, and classified them into species based on leaf morphology. Twelve nuclear microsatellite markers were genotyped in each sample, and analysed using principal coordinates analysis and STRUCTURE software. We compared the effects of two different methods of scoring polyploid genotypes on population genetic analyses. We analysed the effect of ploidy, local species abundance and latitude on levels of introgression between the species.Key ResultsLeaf morphology divided our samples into red and white birch, but genetic analyses unexpectedly revealed two groups within red birch, one of which was tetraploid, as expected, but the other of which appeared to have diploid microsatellite genotypes. Five individuals were identified as early-generation hybrids or backcrosses between white birch and red birch and five were identified between red birch and ‘diploid’ red birch. Cline analysis showed that levels of admixture were not significantly correlated with latitude. Estimated genetic differentiation among species was not significantly different between determined tetraploid and undetermined tetraploid genotypes.ConclusionsLimited hybridization and gene flow have occurred between red birch and white birch. Relative species abundance and ploidy level do not impact the direction of introgression between them, as genetic admixture is roughly symmetrical. We unexpectedly found populations of apparently diploid red birch and this taxon may be a progenitor of allotetraploid red birch populations. Incomplete lineage sorting may explain patterns of genetic admixture between apparently diploid and allotetraploid red birch.

Species diversification in a lineage of Mexican red oak (Quercus section Lobatae subsection Racemiflorae)—the interplay between distance, habitat, and hybridization

In widespread taxa in which hybridization is suspected of being an important aspect of species biology, the patterns and drivers of lineage diversification are not always clear. Here, we examine the patterns of species diversification in a monophyletic lineage of oaks endemic to western Mexico, a center of global oak diversity. This group of four species inhabits a variety of soil types and exhibits varying patterns of species distribution ranging from widespread to restricted, with the range bisected by the Trans-Mexican Volcanic Belt (TVB). Using chloroplast and nuclear microsatellites, we evaluated genetic diversity, diversification, and genetic group assignment across 49 populations. Chloroplast data identified 29 haplotypes in three distinct lineages, many of these found occurring on opposite sides of the TVB. Individual species were only loosely associated to specific chloroplast haplotypes but the distribution of shared haplotypes supports a one-time wider distribution. One lineage was highly divergent and geographically isolated, likely representing a case of chloroplast capture via hybridization and may indicate a range expansion of Racemiflorae into new territory. Nuclear gene diversity varied little across species and populations; however, differentiation and genetic assignment analysis was strongly structured geographically and tended to cluster with broad soil types. Soil specialist taxa produced homogeneous genetic structure while soil generalists showed varying patterns of mixed ancestry and high levels of admixture. Speciation appears driven by a combination of distance and edaphic factors leading to drift. Hybridization appears to be complementary, occurring most often in non-specific soil environments and in marginal areas, and contributes to a long-scale pattern of gene exchange as species ranges fluctuate with time.

Population Pharmacogenomics for Precision Public Health in Colombia.

While genomic approaches to precision medicine hold great promise, they remain prohibitively expensive for developing countries. The precision public health paradigm, whereby healthcare decisions are made at the level of populations as opposed to individuals, provides one way for the genomics revolution to directly impact health outcomes in the developing world. Genomic approaches to precision public health require a deep understanding of local population genomics, which is still missing for many developing countries. We are investigating the population genomics of genetic variants that mediate drug response in an effort to inform healthcare decisions in Colombia. Our work focuses on two neighboring populations with distinct ancestry profiles: Antioquia and Chocó. Antioquia has primarily European genetic ancestry followed by Native American and African components, whereas Chocó shows mainly African ancestry with lower levels of Native American and European admixture. We performed a survey of the global distribution of pharmacogenomic variants followed by a more focused study of pharmacogenomic allele frequency differences between the two Colombian populations. Worldwide, we found pharmacogenomic variants to have both unusually high minor allele frequencies and high levels of population differentiation. A number of these pharmacogenomic variants also show anomalous effect allele frequencies within and between the two Colombian populations, and these differences were found to be associated with their distinct genetic ancestry profiles. For example, the C allele of the single nucleotide polymorphism (SNP) rs4149056 [Solute Carrier Organic Anion Transporter Family Member 1B1 (SLCO1B1)∗5], which is associated with an increased risk of toxicity to a commonly prescribed statin, is found at relatively high frequency in Antioquia and is associated with European ancestry. In addition to pharmacogenomic alleles related to increased toxicity risk, we also have evidence that alleles related to dosage and metabolism have large frequency differences between the two populations, which are associated with their specific ancestries. Using these findings, we have developed and validated an inexpensive allele-specific PCR assay to test for the presence of such population-enriched pharmacogenomic SNPs in Colombia. These results serve as an example of how population-centered approaches to pharmacogenomics can help to realize the promise of precision medicine in resource-limited settings.

MICROSCOPICAL AND MICROMECHANICAL FEATURES OF HIGH PERFORMANCE CONCRETE CONTAINING LOW LEVELS OF FLY ASH

Alkali activated fly ash is a widely used admixture to the concrete. Due to the pozzolanic activity, the fly ash can replace up to 60 mass percentage. The impact of fly ash on the concrete depend on the level of it content, i.e. in small levels it improves the macro-mechanical properties and durability as well as chemical resistance. On the other side, fly ash admixture negatively influence the set time and cause slow development of strength. Therefore, the effect of small fly ash admixture levels on the micro-structure of high performance concrete (HPC) is discussed in this study.

Dissecting the Pre-Columbian Genomic Ancestry of Native Americans along the Andes-Amazonia Divide.

Extensive European and African admixture coupled with loss of Amerindian lineages makes the reconstruction of pre-Columbian history of Native Americans based on present-day genomes extremely challenging. Still open questions remain about the dispersals that occurred throughout the continent after the initial peopling from the Beringia, especially concerning the number and dynamics of diffusions into South America. Indeed, if environmental and historical factors contributed to shape distinct gene pools in the Andes and Amazonia, the origins of this East-West genetic structure and the extension of further interactions between populations residing along this divide are still not well understood.To this end, we generated new high-resolution genome-wide data for 229 individuals representative of one Central and ten South Amerindian ethnic groups from Mexico, Peru, Bolivia, and Argentina. Low levels of European and African admixture in the sampled individuals allowed the application of fine-scale haplotype-based methods and demographic modeling approaches. These analyses revealed highly specific Native American genetic ancestries and great intragroup homogeneity, along with limited traces of gene flow mainly from the Andes into Peruvian Amazonians. Substantial amount of genetic drift differentially experienced by the considered populations underlined distinct patterns of recent inbreeding or prolonged isolation. Overall, our results support the hypothesis that all non-Andean South Americans are compatible with descending from a common lineage, while we found low support for common Mesoamerican ancestors of both Andeans and other South American groups. These findings suggest extensive back-migrations into Central America from non-Andean sources or conceal distinct peopling events into the Southern Continent.

Chimerism and population dieback alter genetic inference related to invasion pathways and connectivity of biofouling populations on artificial substrata.

Disentangling pathways by which nonindigenous species expand and spread regionally remains challenging. Molecular ecology tools are often employed to determine the origins and spread of introduced species, but the complexities of some organisms may be reducing the efficacy of these tools. Some colonial species exhibit complexities by way of chimerism and winter colony regression, which may alter the genetic diversity of populations and mask the connectivity occurring among them. This study uses nuclear microsatellite data and simple GIS‐based modeling to investigate the influence of chimerism and winter regression on the genetic diversity and patterns of genetic population connectivity among colonies of Didemnum vexillum on artificial substrates. Colonies sampled in summer were shown to form a metapopulation, with high levels of admixture, extreme outcrossing, and some substructure. These patterns were consistent within the subsampled winter colonies and with the inclusion of chimeric data. However, allelic richness and diversity were significantly different between winter and summer samples, altering interpretations relating to population connectivity and pelagic larval duration. This study demonstrates the importance of including seasonal sampling and imperative life history traits in genetic studies for clear interpretations and the successful management of introduced species.