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73 results for “genetic introgression”
Selection against individuals from genetic introgression of escaped farmed salmon in a natural population of Atlantic salmon
<p>The viability of wild Atlantic salmon populations is threatened by genetic introgression from escaped farmed salmon. Farmed Atlantic salmon are genetically improved for important commercial traits and a life in captivity but are poorly adapted to the natural environment. The rate of geneflow from escaped farmed to wild salmon depends on their spawning success and on offspring survival at various life-stages. We here investigate relative survival of introgressed juvenile Atlantic salmon (parr) in a river in northern Norway. The studied population has experienced genetic introgression from farmed salmon for about four generations (20 years). We followed two cohorts of parr from the year of hatching (0+) to the age of two years (2+). Farmed genetic introgression was quantified at the individual level and on a continuous scale using diagnostic SNPs. Population-level genetic introgression decreased from 0+ to 2+ by 64% (2011 cohort) and 37% (2013 cohort) . This change was driven by a 70% (2011 cohort) and 49% (2013 cohort) lower survival from age 0+ to 2+ in introgressed parr compared to parr of wild origin. Our observations show that there is natural selection against genetic introgression with a potential cost of lower productivity.The viability of wild Atlantic salmon populations is threatened by genetic introgression from escaped farmed salmon. Farmed Atlantic salmon are genetically improved for important commercial traits and a life in captivity but are poorly adapted to the natural environment. The rate of geneflow from escaped farmed to wild salmon depends on their spawning success and on offspring survival at various life-stages. We here investigate relative survival of introgressed juvenile Atlantic salmon (parr) in a river in northern Norway. The studied population has experienced genetic introgression from farmed salmon for about four generations (20 years). We followed two cohorts of parr from the year of hatching (0+) to the age of two years (2+). Farmed genetic introgression was quantified at the individual level and on a continuous scale using diagnostic SNPs. Population-level genetic introgression decreased from 0+ to 2+ by 64% (2011 cohort) and 37% (2013 cohort) . This change was driven by a 70% (2011 cohort) and 49% (2013 cohort) lower survival from age 0+ to 2+ in introgressed parr compared to parr of wild origin. Our observations show that there is natural selection against genetic introgression with a potential cost of lower productivity.</p>
Archived data for: Balancing selection, genetic drift, and human mediated-introgression interplay to shape MHC (functional) diversity in Mediterranean brown trout
<p>The extraordinary polymorphism of Major Histocompatibility Complex (MHC) genes is considered a paradigm of pathogen-mediated balancing selection, although empirical evidence is still scarce. Furthermore, the relative contribution of balancing selection to shape MHC population structure and diversity, compared to that of neutral forces, as well as its interaction with other evolutionary processes such as hybridization, remains largely unclear. To investigate these issues, we analysed adaptive (MHC-DAB gene) and neutral (11 microsatellite loci) variation in 156 brown trout (<i>Salmo trutta </i>complex) from six wild populations in central Italy exposed to introgression from domestic hatchery lineages (assessed with the LDH gene). MHC diversity and structuring correlated with those at microsatellites, indicating the substantial role of neutral forces. However, individuals carrying locally rare MHC alleles/supertypes (regardless of the zygosity status and degree of sequence dissimilarity of MHC) were in better body condition (a proxy of individual fitness/parasite load), hence supporting balancing selection under rare allele advantage, but not heterozygote advantage or divergent allele advantage. The association between specific MHC supertypes and body condition confirmed in part this finding. Across populations, MHC allelic richness increased with increasing admixture between native and domestic lineages, indicating introgression as a source of MHC variation. Furthermore, introgression across populations appeared more pronounced for MHC than microsatellites, possibly because initially-rare MHC variants are expected to introgress more readily under rare allele advantage. Providing evidence for the complex interplay among neutral evolutionary forces, balancing selection and human-mediated introgression in shaping the pattern of MHC (functional) variation, our findings contribute to a deeper understanding of the evolution of MHC genes in wild populations exposed to anthropogenic disturbance.</p>
Benefit of introgression depends on genetic variation in cereal breeding programs
<p class="MsoBodyText"><span>We investigated the benefit from introgression of external lines into a cereal breeding program and strategies that accelerated introgression of the favourable alleles while minimising linkage drag using stochastic computer simulation. We simulated genomic selection for disease resistance and grain yield in two environments with a high level of genotype-by-environment (G×E) for the latter trait, using genomic data of a historical barley breeding program as the base generation. Two populations (existing and external) were created from this base population with different allele frequencies for few (N=10) major and many (N~990) minor simulated disease quantitative trait loci (QTL). The major disease QTL only existed in the external population and lines from the external population were introgressed into the existing population which had minor disease QTL with low, medium, and high allele frequencies. The study revealed that the benefit of introgression depended on the level of genetic variation for the target trait in the existing cereal breeding program. Introgression of external resources into the existing population was beneficial only when the existing population lacked variation in disease resistance or when minor disease QTL were already at medium or high frequency. When minor disease QTL were at low frequencies, no extra genetic gain was achieved from introgression. More benefit in the disease trait was obtained from the introgression if the major disease QTL had larger effect sizes, more selection emphasis was applied on disease resistance, or more external lines were introgressed. While our strategies to increase introgression of major disease QTL were generally successful, most were not able to completely avoid negative impacts on selection for grain yield with the only exception being when major introgression QTL effects were very large. Breeding programs are advised to carefully consider the level of genetic variation in a trait available in their breeding program before deciding to introgress germplasms.</span></p>
A case of forensic genomics in Uganda reveals animal ownership and low exotic genetic introgression in indigenous cattle
<p class="MsoNormal"><span>The cattle industry contributes to Uganda's agricultural output. It however faces challenges that include theft and parentage ascertainment. These challenges can benefit from recent developments in genomics and bioinformatics technologies. In the current study, we provided a proof-of-concept conflict resolution method based on the available bovine genomic tools. Briefly, two farmers we refer to as A and B contested for ownership of a group of 9 cattle. To offer objective and data-based guidance to resolving this conflict, we sampled hair samples of the 9 contested cattle as well as 7 and 2 cattle from farmers A and B respectively that were identified by these farmers as the closest relatives of the contested animals. DNA was extracted from each of the collected hair samples and subsequently genotyped on the Illumina BovineSNP50-24 version 3 BeadChip for 53218 DNA Single Nucleotide Polymorphisms (SNP) variants. Upon genotype data cleaning we retained ~30,000 SNPs which were used for different genomic analyses including principal component analysis, identity by state (IBS) analysis, and hierarchical clustering analysis, to establish the genetic relationships within and between the investigated animal groups.</span></p>
Comparative transmission genetics of introgressed chromatin in reciprocal advanced backcross populations in Gossypium (cotton) polyploids
<p>Introgression is a potential source of valuable genetic variation and interspecific introgression lines are important resources for plant breeders to access novel alleles. Experimental advanced-generation backcross populations contain individuals with genomic compositions similar to those resulting from natural interspecific hybridization and provide opportunities to study the nature and transmission pattern of donor chromatin in recipient genomes. Here, we analyze transmission of donor chromatin in reciprocal backcrosses between <em>G. hirsutum</em> and <em>G. barbadense</em>. Across the genome, recurrent backcrossing in both backgrounds yielded donor chromatin at slightly higher frequencies than the Mendelian expectation in BC<sub>5</sub>F<sub>1</sub> plants, while the average frequency of donor alleles in BC<sub>5</sub>F<sub>2</sub> segregating families was less than expected. In the two subgenomes of polyploid cotton, the rate of donor chromatin introgression was similar. Although donor chromatin was tolerated over much of the recipient genomes, 21 regions recalcitrant to donor alleles were identified. Only limited correspondence is observed between the recalcitrant regions in the two backgrounds, suggesting the effect of species background on introgression of donor segments. Genetic breakdown was progressive, with floral abscission and seed inviability ongoing during backcrossing cycles. Regions of either high or low introgression tended to be in terminal chromosomal regions that are generally rich in both genes and crossover events, with long stretches around the centromere having limited crossover activity resulting in relatively constant low introgression frequencies. Constraints on fixation and selection of donor alleles highlights the challenges of utilizing introgression breeding in crop improvement.</p>
Benefit of introgression depends on genetic variation in cereal breeding programs
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Selection against individuals from genetic introgression of escaped farmed salmon in a natural population of Atlantic salmon
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A case of forensic genomics in Uganda reveals animal ownership and low exotic genetic introgression in indigenous cattle
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Comparative transmission genetics of introgressed chromatin in reciprocal advanced backcross populations in Gossypium (cotton) polyploids
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Archived data for: Balancing selection, genetic drift, and human mediated-introgression interplay to shape MHC (functional) diversity in Mediterranean brown trout
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Data for paper: The making of a genetic cline: introgression of oceanic genes into coastal cod populations in the North East Atlantic
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Data from: Genetic introgression among differentiated clades is lower among clades exhibiting different parity modes
Mechanisms leading to sympatric speciation are diverse and may build up reproductive isolation. Reproductive isolation among differentiated clades may exist due to genetic incompatibilities, sexual selection, differences in parity mode, reduced post-zygotic survival or reproductive success of hybrids. Here we test whether differences in parity mode lead to reproductive isolation by investigating introgression in Zootoca vivipara, a lizard species exhibiting oviparous and viviparous reproduction. We measured introgression in transects spanning different viviparous clades, different oviparous subclades, transects containing oviparous and viviparous clades, and transects within the same subclade (control transects). Introgression in transects spanning oviparous and viviparous clades was one order of magnitude smaller than transects spanning the same reproductive mode and no statistical differences existed between transects spanning the same reproductive mode and contr ol transects. Among types of transects, no significant differences existed in genetic and geographic distances, nor number of detected alleles. Moreover, hybrids were detected in all types of transects, showing that parity mode alone does not necessarily lead to complete reproductive isolation, which suggests that reinforcement may play an important role. The evolution of different parity modes together with reinforcement may thus promote reproductive isolation and rapid speciation, potentially explaining why only six of the almost 40'000 vertebrates belonging to groups consisting of viviparous and oviparous species exhibit bimodal reproduction.
Asymmetric acoustic signal recognition led to asymmetric genetic introgression between two parapatric rhacophorid treefrogs
<p><span>Correct discrimination between courtship signals could help maintain genetic integrity between closely related species. However, asymmetric usage of signals might cause asymmetric magnitude of gene flow across the contact zone. <i>Buergeria japonica </i>and <i>B. otai </i>are sibling species with parapatric distribution pattern in Taiwan, forming two narrow contact zones in eastern and western sides of the island. Both species use a shared acoustic signal of calls (Type 1a/1b), whereas <i>B. otai </i>presents another unique call type (Type 2) which never appears in <i>B. japonica</i>. Combining behavioral experiments with genome-wide RAD-seq analyses, we aim to test whether the ability of signal recognition influences genetic introgression across their species boundary. The playback experiments showed that the western population of <i>B. otai</i> has evolved a stronger level of reproductive character displacement by showing the inclusive usage of their unique Type 2 signal. In contrast, the eastern population used both unique and shared signals and has a stronger preference for the latter. Consistent with behavioral difference, genetic introgression across the contact zone was detected only in the eastern boundary but not in the western one. Furthermore, the gene flow in this contact zone tends to be unidirectional from <i>B. japonica</i> toward <i>B. otai</i>. Our results support the prediction that a more specialized signal user might have a higher probability to maintain their genetic integrity compared to a generalized signal user.</span></p>
Data from: Intermediate habitat associations by hybrids may facilitate genetic introgression in a songbird
Hybridization or the interbreeding of genetically discrete populations or species can occur where ranges of genetically distinct units overlap. Golden-winged warblers Vermivora chrysoptera, a species that has been in steady decline for decades, highlight the potential population-level consequences of hybridization. A major factor implicated in their decline is hybridization with their sister species, the blue-winged warbler Vermivora cyanoptera, which has likely been exacerbated by historic and current land-use practices. We examined habitat associations of golden-winged and blue-winged warblers, phenotypic hybrids, and cryptic hybrids (i.e. mismatch between plumage phenotype and genotype as identified by mitochondrial DNA) in an area of relatively recent range overlap and hybridization in northern New York, USA. To explore the robustness of these results, we then compared the patterns from New York with habitat associations from the central Pennsylvanian Appalachian Mountains where blue-winged warblers either do not occur or are in very low abundance, yet cryptic golden-winged warbler hybrids are present. From 2008 to 2011, we captured 122 birds in New York and 28 in Pennsylvania and collected blood samples, which we used to determine maternal ancestry. For each bird captured, we measured territory-level (50-m radius circles) habitat, and later used remote-sensing data to quantify habitat on the territories and in surrounding areas (100-, 250-, and 500-m radius circles). In New York, golden-winged warblers occupied structurally heterogeneous territories surrounded by homogeneously structured, contiguous deciduous forest, far from urban areas. Blue-winged warblers showed opposite associations, and hybrids' habitat associations were typically intermediate. In Pennsylvania, the habitat associations of golden-winged warblers and their cryptic hybrids were remarkably similar to those in New York. These findings suggest that patterns of habitat occupancy by hybrids may promote contact with golden-winged warblers and thus likely facilitate genetic introgression, even in areas where the parental species are not sympatric.
Data from: RAD-seq reveals genetic structure of the F2-generation of natural willow hybrids (Salix L.) and a great potential for interspecific introgression
Background: Hybridization of species with porous genomes can eventually lead to introgression via repeated backcrossing. The potential for introgression between species is reflected by the extent of segregation distortion in later generation hybrids. Here we studied a population of hybrids between Salix purpurea and S. helvetica that has emerged within the last 30 years on a glacier forefield in the European Alps due to secondary contact of the parental species. We used 5,758 biallelic SNPs produced by RAD sequencing with the aim to ascertain the predominance of backcrosses (F1 hybrid x parent) or F2 hybrids (F1 hybrid x F1 hybrid) among hybrid offspring. Further, the SNPs were used to study segregation distortion in the second hybrid generation. Results: The analyses in STRUCTURE and NewHybrids revealed that the population consisted of parents and F1 hybrids, whereas hybrid offspring consisted mainly of backcrosses to either parental species, but also some F2 hybrids. Although there was a clear genetic differentiation between S. purpurea and S. helvetica (FST = 0.24), there was no significant segregation distortion in the backcrosses or the F2 hybrids. Plant height of the backcrosses resembled the respective parental species, whereas F2 hybrids were more similar to the subalpine S. helvetica. Conclusions: The co-occurrence of the parental species and the hybrids on the glacier forefield, the high frequency of backcrossing, and the low resistance to gene flow via backcrossing make a scenario of introgression in this young hybrid population highly likely, potentially leading to the transfer of adaptive traits. We further suggest that this willow hybrid population may serve as a model for the evolutionary processes initiated by recent global warming.
Data from: Genetic admixing of two evergreen oaks, Quercus acuta and Q. sessilifolia (subgenus Cyclobalanopsis), is the result of interspecific introgressive hybridization
In forests worldwide, Quercus is a major genus; however, the boundaries between the constituent species are relatively weak, and hybridization is reported frequently. In this study, we examined Quercus acuta and Quercus sessilifolia (subgenus Cyclobalanopsis), which have a putative hybrid—Q. x takaoyamensis. We investigated leaf morphological traits and microsatellites of Q. acuta and Q. sessilifolia in the area where the two species are both found. Although the leaf traits overlapped, the two species could be distinguished morphologically as demonstrated by principal component analysis based on a range of these traits. They were also genetically differentiated, with F ST = 0.104. However, they shared most of the alleles at all eight loci examined, and considerable genetic admixing was detected. Admixture analysis demonstrated that Q. acuta and Q. sessilifolia, respectively, contained 11 and 24 % of individuals with a probability of less than 0.9 of being correctly assigned to their species. Model-based testing showed that this admixing was created by not only shared ancestral polymorphism but also by hybridization. Effective population size and migration rate were estimated using the coalescent approach. We estimated 8.843 and 71.98 effective numbers of migrants per generation to Q. acuta and Q. sessilifolia, respectively. Theoretically, one to ten migrants per generation are required to prevent complete genetic differentiation. Based on the results of this study, it appears that genetic admixing, with sharing of most alleles, is probably common in the two species and is maintained by interspecific introgressive hybridization.
Data from: The hidden history of the snowshoe hare, Lepus americanus: extensive mitochondrial DNA introgression inferred from multilocus genetic variation
Hybridization drives the evolutionary trajectory of many species or local populations, and assessing the geographic extent and genetic impact of interspecific gene flow may provide invaluable clues to understand population divergence or the adaptive relevance of admixture. In North America, hares (Lepus spp.) are key species for ecosystem dynamics and their evolutionary history may have been affected by hybridization. Here we reconstructed the speciation history of the three most widespread hares in North America - the snowshoe hare (Lepus americanus), the white-tailed jackrabbit (L. townsendii) and the black-tailed jackrabbit (L. californicus) - by analyzing sequence variation at eight nuclear markers and one mitochondrial DNA (mtDNA) locus (6 240 bp; 94 specimens). A multilocus-multispecies coalescent-based phylogeny suggests that L. americanus diverged ~2.7 Mya and that L. californicus and L. townsendii split more recently (~1.2 Mya). Within L. americanus a deep history of cryptic divergence (~2.0 Mya) was inferred, which coincides with major speciation events in other North American species. While the isolation-with-migration model suggested that nuclear gene flow was generally rare or absent among species or major genetic groups, coalescent simulations of mtDNA divergence revealed historical mtDNA introgression from L. californicus into the Pacific Northwest populations of L. americanus. This finding marks a history of past reticulation between these species, which may have affected other parts of the genome and influence the adaptive potential of hares during climate change.
Data from: The eastern migratory caribou: the role of genetic introgression in ecotype evolution
Understanding the evolutionary history of contemporary animal groups is essential for conservation and management of endangered species like caribou (Rangifer tarandus). In central Canada, the ranges of two caribou subspecies (barren-ground/woodland caribou) and two woodland caribou ecotypes (boreal/eastern migratory) overlap. Our objectives were to reconstruct the evolutionary history of the eastern migratory ecotype and to assess the potential role of introgression in ecotype evolution. STRUCTURE analyses identified five higher order groups (i.e. three boreal caribou populations, eastern migratory ecotype and barren-ground). The evolutionary history of the eastern migratory ecotype was best explained by an early genetic introgression from barren-ground into a woodland caribou lineage during the Late Pleistocene and subsequent divergence of the eastern migratory ecotype during the Holocene. These results are consistent with the retreat of the Laurentide ice sheet and the colonization of the Hudson Bay coastal areas subsequent to the establishment of forest tundra vegetation approximately 7000 years ago. This historical reconstruction of the eastern migratory ecotype further supports its current classification as a conservation unit, specifically a Designatable Unit, under Canada's Species at Risk Act. These findings have implications for other sub-specific contact zones for caribou and other North American species in conservation unit delineation.
Data from: SNPs selected by information content outperform randomly selected microsatellite loci for delineating genetic identification and introgression in the endangered dark European honeybee (Apis mellifera mellifera)
The honeybee (Apis mellifera) has been threatened by multiple factors, including pests and pathogens, pesticides, and loss of locally adapted gene complexes due to replacement and introgression. In western Europe, the genetic integrity of the native A.m. mellifera (M-lineage) is endangered due to trading and intensive queen breeding with commercial subspecies of eastern European ancestry (C-lineage). Effective conservation actions require reliable molecular tools to identify purebred A.m. mellifera colonies. Microsatellites have been preferred for identification of A.m. mellifera stocks across conservation centers. However, owing to high-throughput, easy transferability between laboratories and low genotyping error, SNPs promise to become popular. Here, we compared the resolving power of a widely utilized microsatellite dataset to detect structure and introgression with that of different datasets that combine a variable number of SNPs selected for their information content and genomic proximity to the microsatellites. Contrary to every SNP dataset, microsatellites were unable to clearly separate the two European lineages in the PCA space. Mean introgression proportions were identical across the two marker types, although at the individual level microsatellites' performance was relatively poor at the upper range of introgression, a result reflected by their lower precision. Although mean accuracy was relatively high across datasets (>91%), microsatellites were the least accurate and the top-ranked informative 144 SNPs were the most accurate. Comparisons amongst the SNP datasets showed that those combining SNPs flanking microsatellites performed worst. Our results suggest that SNPs are more powerful for identification of A.m. mellifera colonies, especially when they are selected by information content.
Data from: Lack of genetic introgression between wild and selectively bred Sydney rock oysters Saccostrea glomerata
Sydney rock oysters Saccostrea glomerata are among the most important estuarine species on the eastern coast of Australia and also the basis of a major aquaculture industry. The industry now largely relies on Sydney rock oysters that have been selectively bred for fast growth and disease resistance. Selectively bred S. glomerata are currently farmed in estuaries that also sustain wild populations of Sydney rock oysters, providing the opportunity for interbreeding. This has led to concern that gene flow from farmed, selectively bred oysters could alter the genetic variability of wild oyster populations. Here, we use next-generation genotype-by-sequencing to test for genetic introgression between wild and farmed, selectively bred (B2 line) Sydney rock oysters from 2 sites in the Georges River, NSW. Strong genetic partitioning was identified between the wild and selectively bred populations. There was no evidence of gene flow in the form of introgression, even though selectively bred B2 oysters have been farmed in the Georges River since the early 1990s. Contrary to our expectations, we also found significantly higher levels of genetic diversity and heterozygosity in the selectively bred population relative to the wild population. The relatively low level of genetic diversity that we detected in wild oysters may be particularly relevant to the adaptive capacity of this species in the wild.
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