Artigos de revistas: "Gene flow barrier"

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Tavares, Hugo, Annabel Whibley, David L. Field, Desmond Bradley, Matthew Couchman, Lucy Copsey, Joane Elleouet et al. "Selection and gene flow shape genomic islands that control floral guides". Proceedings of the National Academy of Sciences 115, n.º 43 (8 de outubro de 2018): 11006–11. http://dx.doi.org/10.1073/pnas.1801832115.

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Genomes of closely-related species or populations often display localized regions of enhanced relative sequence divergence, termed genomic islands. It has been proposed that these islands arise through selective sweeps and/or barriers to gene flow. Here, we genetically dissect a genomic island that controls flower color pattern differences between two subspecies of Antirrhinum majus, A.m.striatum and A.m.pseudomajus, and relate it to clinal variation across a natural hybrid zone. We show that selective sweeps likely raised relative divergence at two tightly-linked MYB-like transcription factors, leading to distinct flower patterns in the two subspecies. The two patterns provide alternate floral guides and create a strong barrier to gene flow where populations come into contact. This barrier affects the selected flower color genes and tightly-linked loci, but does not extend outside of this domain, allowing gene flow to lower relative divergence for the rest of the chromosome. Thus, both selective sweeps and barriers to gene flow play a role in shaping genomic islands: sweeps cause elevation in relative divergence, while heterogeneous gene flow flattens the surrounding “sea,” making the island of divergence stand out. By showing how selective sweeps establish alternative adaptive phenotypes that lead to barriers to gene flow, our study sheds light on possible mechanisms leading to reproductive isolation and speciation.

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BARTON, N. H. "The effect of a barrier to gene flow on patterns of geographic variation". Genetics Research 90, n.º 1 (fevereiro de 2008): 139–49. http://dx.doi.org/10.1017/s0016672307009081.

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SummaryExplicit formulae are given for the effects of a barrier to gene flow on random fluctuations in allele frequency; these formulae can also be seen as generating functions for the distribution of coalescence times. The formulae are derived using a continuous diffusion approximation, which is accurate over all but very small spatial scales. The continuous approximation is confirmed by comparison with the exact solution to the stepping stone model. In both one and two spatial dimensions, the variance of fluctuations in allele frequencies increases near the barrier; when the barrier is very strong, the variance doubles. However, the effect on fluctuations close to the barrier is much greater when the population is spread over two spatial dimensions than when it occupies a linear, one-dimensional habitat: barriers of strength comparable with the dispersal range (B≈σ) can have an appreciable effect in two dimensions, whereas only barriers with strength comparable with the characteristic scale (B\! \approx\! L \equals \sigma \sol \sqrt {2 \mu}\hskip2) are significant in one dimension (μ is the rate of mutation or long-range dispersal). Thus, in a two-dimensional population, barriers to gene flow can be detected through their effect on the spatial pattern of genetic marker alleles.

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Joannon, B., C. Lavigne, H. Lecoq e C. Desbiez. "Barriers to Gene Flow Between Emerging Populations of Watermelon mosaic virus in Southeastern France". Phytopathology® 100, n.º 12 (dezembro de 2010): 1373–79. http://dx.doi.org/10.1094/phyto-04-10-0118.

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Since 1999, “emerging” (EM) strains of Watermelon mosaic virus (WMV) have been detected in cucurbit crops of southeastern France, probably as a result of recent introductions. Population genetic approaches were used to study the structure of EM isolates in southeastern France and to identify factors involved in their spatial distribution. A population clustering method (SAMOVA) and a maximum-difference algorithm (Monmonier's algorithm) were combined to visualize and quantify barriers to gene flow between populations. Both methods yielded similar results and two main barriers were identified. A North/South oriented barrier may be related to physical obstacles to gene flow (Rhône River, presence of an area with few cucurbit crops). Although the barrier was very strong, some “crossing” events were detected. A second barrier, oriented Northwest to Southeast, was not correlated with obvious geographical features. The two methods used here are complementary and confirm the limited spread of WMV-EM isolates. This approach can be useful in epidemiology studies to characterize the structure of viral populations and identify barriers to gene flow.

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Laetsch, Dominik R., Gertjan Bisschop, Simon H. Martin, Simon Aeschbacher, Derek Setter e Konrad Lohse. "Demographically explicit scans for barriers to gene flow using gIMble". PLOS Genetics 19, n.º 10 (10 de outubro de 2023): e1010999. http://dx.doi.org/10.1371/journal.pgen.1010999.

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Identifying regions of the genome that act as barriers to gene flow between recently diverged taxa has remained challenging given the many evolutionary forces that generate variation in genetic diversity and divergence along the genome, and the stochastic nature of this variation. Progress has been impeded by a conceptual and methodological divide between analyses that infer the demographic history of speciation and genome scans aimed at identifying locally maladaptive alleles i.e. genomic barriers to gene flow. Here we implement genomewide IM blockwise likelihood estimation (gIMble), a composite likelihood approach for the quantification of barriers, that bridges this divide. This analytic framework captures background selection and selection against barriers in a model of isolation with migration (IM) as heterogeneity in effective population size (Ne) and effective migration rate (me), respectively. Variation in both effective demographic parameters is estimated in sliding windows via pre-computed likelihood grids. gIMble includes modules for pre-processing/filtering of genomic data and performing parametric bootstraps using coalescent simulations. To demonstrate the new approach, we analyse data from a well-studied pair of sister species of tropical butterflies with a known history of post-divergence gene flow: Heliconius melpomene and H. cydno. Our analyses uncover both large-effect barrier loci (including well-known wing-pattern genes) and a genome-wide signal of a polygenic barrier architecture.

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de Abreu Moreira, Patrícia, e G. Wilson Fernandes. "Is the São Francisco River a geographic barrier to gene flow in trees of Handroanthus ochraceus?" Journal of Tropical Ecology 29, n.º 3 (19 de abril de 2013): 243–50. http://dx.doi.org/10.1017/s0266467413000217.

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Abstract:Many landscape features represent geographic barriers to gene flow, and promote genetic discontinuity. Rivers are effective barriers. However, most studies on this subject have focused on animals and only a few have focused on plants. We studied the genetic structure and gene flow of the tropical tree Handroanthus ochraceus (Bignoniaceae) on both banks of the São Francisco River in a Brazilian seasonally dry tropical forest. The São Francisco is located in eastern Brazil and is 600 m wide at the study site. Our hypothesis was that the river is a geographic barrier to gene flow of H. ochraceus trees. We sampled two populations on the left bank and one population on the right bank. We used seven microsatellites to genotype 212 individual plants. All populations had low polymorphism and genetic diversity, but high inbreeding. There was no genetic differentiation among populations and, consequently, the estimated gene flow was high for all pairs of populations. The genetic relatedness among individuals from populations of the same margin did not differ from the relatedness among individuals from populations of opposite margins. Hence, the São Francisco River is not an effective geographic barrier to gene flow among H. ochraceus populations.

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Hu, Xin-Sheng. "Mating system as a barrier to gene flow". Evolution 69, n.º 5 (maio de 2015): 1158–77. http://dx.doi.org/10.1111/evo.12660.

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Gross, Liza. "Autoimmunity: A Barrier to Gene Flow in Plants?" PLoS Biology 5, n.º 9 (4 de setembro de 2007): e262. http://dx.doi.org/10.1371/journal.pbio.0050262.

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Lessios, H. A. "A sea water barrier to coral gene flow". Molecular Ecology 21, n.º 22 (29 de outubro de 2012): 5390–92. http://dx.doi.org/10.1111/mec.12037.

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Gayden, Tenzin, Annabel Perez, Patrice J. Persad, Areej Bukhari, Shilpa Chennakrishnaiah, Tanya Simms, Trisha Maloney, Kristina Rodriguez e Rene J. Herrera. "The Himalayas: Barrier and conduit for gene flow". American Journal of Physical Anthropology 151, n.º 2 (12 de abril de 2013): 169–82. http://dx.doi.org/10.1002/ajpa.22240.

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Christmas, Matthew J., Julia C. Jones, Anna Olsson, Ola Wallerman, Ignas Bunikis, Marcin Kierczak, Valentina Peona et al. "Genetic Barriers to Historical Gene Flow between Cryptic Species of Alpine Bumblebees Revealed by Comparative Population Genomics". Molecular Biology and Evolution 38, n.º 8 (6 de abril de 2021): 3126–43. http://dx.doi.org/10.1093/molbev/msab086.

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Abstract Evidence is accumulating that gene flow commonly occurs between recently diverged species, despite the existence of barriers to gene flow in their genomes. However, we still know little about what regions of the genome become barriers to gene flow and how such barriers form. Here, we compare genetic differentiation across the genomes of bumblebee species living in sympatry and allopatry to reveal the potential impact of gene flow during species divergence and uncover genetic barrier loci. We first compared the genomes of the alpine bumblebee Bombus sylvicola and a previously unidentified sister species living in sympatry in the Rocky Mountains, revealing prominent islands of elevated genetic divergence in the genome that colocalize with centromeres and regions of low recombination. This same pattern is observed between the genomes of another pair of closely related species living in allopatry (B. bifarius and B. vancouverensis). Strikingly however, the genomic islands exhibit significantly elevated absolute divergence (dXY) in the sympatric, but not the allopatric, comparison indicating that they contain loci that have acted as barriers to historical gene flow in sympatry. Our results suggest that intrinsic barriers to gene flow between species may often accumulate in regions of low recombination and near centromeres through processes such as genetic hitchhiking, and that divergence in these regions is accentuated in the presence of gene flow.

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Gayden, Tenzin, Alicia M. Cadenas, Maria Regueiro, Nanda B. Singh, Lev A. Zhivotovsky, Peter A. Underhill, Luigi L. Cavalli-Sforza e Rene J. Herrera. "The Himalayas as a Directional Barrier to Gene Flow". American Journal of Human Genetics 80, n.º 5 (maio de 2007): 884–94. http://dx.doi.org/10.1086/516757.

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Evans, Ben J., Anthony J. Tosi, Kai Zeng, Jonathan Dushoff, André Corvelo e Don J. Melnick. "Speciation over the edge: gene flow among non-human primate species across a formidable biogeographic barrier". Royal Society Open Science 4, n.º 10 (outubro de 2017): 170351. http://dx.doi.org/10.1098/rsos.170351.

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Many genera of terrestrial vertebrates diversified exclusively on one or the other side of Wallace’s Line, which lies between Borneo and Sulawesi islands in Southeast Asia, and demarcates one of the sharpest biogeographic transition zones in the world. Macaque monkeys are unusual among vertebrate genera in that they are distributed on both sides of Wallace‘s Line, raising the question of whether dispersal across this barrier was an evolutionary one-off or a more protracted exchange—and if the latter, what were the genomic consequences. To explore the nature of speciation over the edge of this biogeographic divide, we used genomic data to test for evidence of gene flow between macaque species across Wallace’s Line after macaques colonized Sulawesi. We recovered evidence of post-colonization gene flow, most prominently on the X chromosome. These results are consistent with the proposal that gene flow is a pervasive component of speciation—even when barriers to gene flow seem almost insurmountable.

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Blanckaert, Alexandre, Claudia Bank e Joachim Hermisson. "The limits to parapatric speciation 3: evolution of strong reproductive isolation in presence of gene flow despite limited ecological differentiation". Philosophical Transactions of the Royal Society B: Biological Sciences 375, n.º 1806 (13 de julho de 2020): 20190532. http://dx.doi.org/10.1098/rstb.2019.0532.

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Gene flow tends to impede the accumulation of genetic divergence. Here, we determine the limits for the evolution of postzygotic reproductive isolation in a model of two populations that are connected by gene flow. We consider two selective mechanisms for the creation and maintenance of a genetic barrier: local adaptation leads to divergence among incipient species due to selection against migrants, and Dobzhansky–Muller incompatibilities (DMIs) reinforce the genetic barrier through selection against hybrids. In particular, we are interested in the maximum strength of the barrier under a limited amount of local adaptation, a challenge that many incipient species may initially face. We first confirm that with classical two-locus DMIs, the maximum amount of local adaptation is indeed a limit to the strength of a genetic barrier. However, with three or more loci and cryptic epistasis, this limit holds no longer. In particular, we identify a minimal configuration of three epistatically interacting mutations that is sufficient to confer strong reproductive isolation. This article is part of the theme issue ‘Towards the completion of speciation: the evolution of reproductive isolation beyond the first barriers’.

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Lee, Tristan, Kyall R. Zenger, Robert L. Close, Marilyn Jones e David N. Phalen. "Defining spatial genetic structure and management units for vulnerable koala (Phascolarctos cinereus) populations in the Sydney region, Australia". Wildlife Research 37, n.º 2 (2010): 156. http://dx.doi.org/10.1071/wr09134.

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Context. Mammal populations around the world are increasingly threatened with population fragmentation because of loss of habitat or barriers to gene flow. The investigation of koala populations in the Sydney region not only provides valuable information about this vulnerable species, but also serves as a model for other species that have suffered major rapid declines in population size, and are now recovering in fragmented habitat. The peri-urban study region allows investigation of the impact of landscape features such as major roads and housing developments on koala gene flow. Aims. Animals originating from four geographic sampling areas around Sydney, New South Wales, Australia, were examined to determine population structure and gene flow and to identify barriers to gene flow and management units. Methods. The present study examined 12 microsatellite loci and used Bayesian assignment methods and genic frequency analysis methods to identify demographically separate populations and barriers to gene flow between those populations. Key results. Three discrete populations were resolved, with all displaying moderate to high levels of genetic differentiation among them (θ = 0.141–0.224). The allelic richness and heterozygosity of the Blue Mountains population (A = 6.46, HO = 0.66) is comparable to the highest diversity found in any koala population previously investigated. However, considerably lower genetic diversity was found in the Campbelltown population (A = 3.17, HO = 0.49), which also displayed evidence of a recent population bottleneck (effective population size estimated at 16–21). Conclusions. Animals separated by a military reserve were identified as one population, suggesting that the reserve maintains gene flow within this population. By contrast, strong differentiation of two geographically close populations separated by several potential barriers to gene flow suggested these land-use features pose barriers to gene flow. Implications. Implications of these findings for management of koala populations in the Greater Sydney region are discussed. In particular, the need to carefully consider the future of a military reserve is highlighted, along with possible solutions to allow gene flow across the proposed barrier regions. Because these are demographically separate populations, specific management plans tailored to the needs of each population will need to be formulated.

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Su, H., L.-J. Qu, K. He, Z. Zhang, J. Wang, Z. Chen e H. Gu. "The Great Wall of China: a physical barrier to gene flow?" Heredity 90, n.º 3 (março de 2003): 212–19. http://dx.doi.org/10.1038/sj.hdy.6800237.

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Lessios, H. A., B. D. Kessing e D. R. Robertson. "Massive gene flow across the world's most potent marine biogeographic barrier". Proceedings of the Royal Society of London. Series B: Biological Sciences 265, n.º 1396 (7 de abril de 1998): 583–88. http://dx.doi.org/10.1098/rspb.1998.0334.

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Lessios, H. A., e D. R. Robertson. "Crossing the impassable: genetic connections in 20 reef fishes across the eastern Pacific barrier". Proceedings of the Royal Society B: Biological Sciences 273, n.º 1598 (7 de junho de 2006): 2201–8. http://dx.doi.org/10.1098/rspb.2006.3543.

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The ‘impassable’ Eastern Pacific Barrier (EPB), ca 5000 km of deep water separating the eastern from the central Pacific, is the World's widest marine biogeographic barrier. Sequencing of mitochondrial DNA in 20 reef fish morphospecies encountered on both sides of the barrier revealed cryptic speciation in two. Among the other 18 species only two showed significant differentiation (as revealed by haplotype networks and F ST statistics) between the eastern and the central Pacific. Coalescence analyses indicated that genetic similarity in the 18 truly transpacific species resulted from different combinations of ages of most recent invasion and of levels of recurrent gene flow, with estimated times of initial separation ranging from approximately 30 000 to 1 Myr (ago). There is no suggestion of simultaneous interruptions of gene flow among the species. Migration across the EPB was previously thought to be exclusively eastward, but our evidence showed two invasions from east to west and eight cases in which subsequent gene flow possibly proceeded in the same direction. Thus, the EPB is sporadically permeable to propagules originating on either side.

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Glass, Jessica R., Scott R. Santos, John SK Kauwe e Brandon D. Pickett. "Phylogeography of two marine predators, giant trevally (Caranx ignobilis) and bluefin trevally (Caranx melampygus), across the Indo-Pacific". Bulletin of Marine Science 97, n.º 2 (1 de abril de 2021): 257–80. http://dx.doi.org/10.5343/bms.2019.0114.

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For economically valuable marine fishes, identifying biogeographic barriers and estimating the extent of gene flow are critical components of fisheries management. We examined the population genetic structure of two commercially important reef-associated predators, the giant trevally ( Caranx ignobilis) and bluefin trevally (Caranx melampygus). We sampled 225 individuals and 32,798 single nucleotide polymorphisms (SNPs) of C. ignobilis, and 74 individuals and 43,299 SNPs of C. melampygus. Analyses of geographic population structure indicate the two species display subtly different phylogeographic patterns. Caranx ignobilis comprises two to three putative populations—one in the Central Pacific, one inhabiting the Western Pacific and Eastern Indian oceans, and one in the Western Indian Ocean—with some restricted gene flow between them. Caranx melampygus shows evidence of restricted gene flow from Hawaii to the West Pacific and Indian oceans, as well as limited genetic connectivity across the Indo- Pacific Barrier. Both species exhibit patterns characteristic of other large, reef-associated predators such as deepwater snappers and the great barracuda. This study contributes to ongoing assessments of the role of the Indo-Pacific Barrier in shaping patterns of phylogeography for large reef-associated fishes. Furthermore, by identifying putative populations of C. ignobilis and C. melampygus in the Central Pacific, our findings serve to improve future management measures for these economically important, data-limited species, particularly in light of historic and contemporary overfishing in Hawaii.

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Sun, Zhonglou, Tao Pan, Hui Wang, Mujia Pang e Baowei Zhang. "Yangtze River, an insignificant genetic boundary in tufted deer (Elaphodus cephalophus): the evidence from a first population genetics study". PeerJ 4 (8 de novembro de 2016): e2654. http://dx.doi.org/10.7717/peerj.2654.

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Great rivers were generally looked at as the geographical barrier to gene flow for many taxonomic groups. The Yangtze River is the third largest river in the world, and flows across South China and into the East China Sea. Up until now, few studies have been carried out to evaluate its effect as a geographical barrier. In this study, we attempted to determine the barrier effect of the Yangtze River on the tufted deer (Elaphodus cephalophus) using the molecular ecology approach. Using mitochondrial DNA control region (CR) sequences and 13 nuclear microsatellite loci, we explored the genetic structure and gene flow in two adjacent tufted deer populations (Dabashan and Wulingshan populations), which are separated by the Yangtze River. Results indicated that there are high genetic diversity levels in the two populations, but no distinguishable haplotype group or potential genetic cluster was detected which corresponded to specific geographical population. At the same time, high gene flow was observed between Wulingshan and Dabashan populations. The tufted deer populations experienced population decrease from 0.3 to 0.09 Ma BP, then followed by a distinct population increase. A strong signal of recent population decline (T= 4,396 years) was detected in the Wulingshan population by a Markov-Switching Vector Autoregressions(MSVAR) process population demography analysis. The results indicated that the Yangtze River may not act as an effective barrier to gene flow in the tufted deer. Finally, we surmised that the population demography of the tufted deer was likely affected by Pleistocene climate fluctuations and ancient human activities.

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Agrawal, Aneil F., Jeffrey L. Feder e Patrik Nosil. "Ecological Divergence and the Origins of Intrinsic Postmating Isolation with Gene Flow". International Journal of Ecology 2011 (2011): 1–15. http://dx.doi.org/10.1155/2011/435357.

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The evolution of intrinsic postmating isolation has received much attention, both historically and in recent studies of speciation genes. Intrinsic isolation often stems from between-locus genetic incompatibilities, where alleles that function well within species are incompatible with one another when brought together in the genome of a hybrid. It can be difficult for such incompatibilities to originate when populations diverge with gene flow, because deleterious genotypic combinations will be created and then purged by selection. However, it has been argued that if genes underlying incompatibilities are themselves subject to divergent selection, then they might overcome gene flow to diverge between populations, resulting in the origin of incompatibilities. Nonetheless, there has been little explicit mathematical exploration of such scenarios for the origin of intrinsic incompatibilities during ecological speciation with gene flow. Here we explore theoretical models for the origin of intrinsic isolation where genes subject to divergent natural selection also affect intrinsic isolation, either directly or via linkage disequilibrium with other loci. Such genes indeed overcome gene flow, diverge between populations, and thus result in the evolution of intrinsic isolation. We also examine barriers to neutral gene flow. Surprisingly, we find that intrinsic isolation sometimes weakens this barrier, by impeding differentiation via ecologically based divergent selection.

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Lanna, Flávia M., Marcelo Gehara, Fernanda P. Werneck, Emanuel M. Fonseca, Guarino R. Colli, Jack W. Sites, Miguel T. Rodrigues e Adrian A. Garda. "Dwarf geckos and giant rivers: the role of the São Francisco River in the evolution of Lygodactylus klugei (Squamata: Gekkonidae) in the semi-arid Caatinga of north-eastern Brazil". Biological Journal of the Linnean Society 129, n.º 1 (22 de novembro de 2019): 88–98. http://dx.doi.org/10.1093/biolinnean/blz170.

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Abstract Species diversification can be strongly influenced by geomorphological features, such as mountains, valleys and rivers. Rivers can act as hard or soft barriers to gene flow depending on their size, speed of flow, historical dynamics and regional topographical characteristics. The São Francisco River (SFR) is the largest perennial river in the Caatinga biome in north-eastern Brazil and has been considered a barrier to gene flow and dispersal. Herein, we evaluated the role of the SFR on the evolution of Lygodactylus klugei, a small gecko from the Caatinga. Using a single-locus species delimitation method (generalized mixed Yule coalescent), we defined lineages (haploclades). Subsequently, we evaluated the role of the SFR in structuring genetic diversity in this species using a multilocus approach to quantify migration across margins. We also evaluated genetic structure based on nuclear markers, testing the number of populations found through an assignment test (STRUCTURE) across the species distribution. We recovered two mitochondrial lineages structured with respect to the SFR, but only a single population was inferred from nuclear markers. Given that we detected an influence of the SFR only on mitochondrial markers, we suggest that the current river course has acted as a relatively recent geographical barrier for L. klugei, for ~450 000 years.

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Bomblies, Kirsten, e Detlef Weigel. "Hybrid necrosis: autoimmunity as a potential gene-flow barrier in plant species". Nature Reviews Genetics 8, n.º 5 (3 de abril de 2007): 382–93. http://dx.doi.org/10.1038/nrg2082.

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Bialozyt, Ronald, Marc Niggemann e Birgit Ziegenhagen. "Quantification of the zygotic barrier between interbreeding taxa using gene flow data". Oikos 126, n.º 7 (14 de dezembro de 2016): 948–58. http://dx.doi.org/10.1111/oik.03428.

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Vikas, V. K., S. M. S. Tomar, M. Sivasamy, Jagdish Kumar, P. Jayaprakash, Arun Kumar, John Peter, R. Nisha e E. Punniakotti. "Hybrid necrosis in wheat: evolutionary significance or potential barrier for gene flow?" Euphytica 194, n.º 2 (20 de junho de 2013): 261–75. http://dx.doi.org/10.1007/s10681-013-0952-9.

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Nagasawa, Koki, Hiroaki Setoguchi, Masayuki Maki, Kazuhiro Sawa, Kenji Horie e Shota Sakaguchi. "Species cohesion of an extremophyte (Carex angustisquama, Cyperaceae) in solfatara fields maintained under interspecific natural hybridization". Annals of Botany 128, n.º 3 (9 de junho de 2021): 343–56. http://dx.doi.org/10.1093/aob/mcab069.

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Abstract Background and Aims Hybridization is the main driver of plant diversification, and gene flow via hybridization has multifaceted effects on plant evolution. Carex angustisquama is an extremophyte that grows on soils heavily acidified by volcanism. Despite its habitat distinct from that of other species, this species is known to form interspecific hybrids, implying interspecific gene flow. It is crucial to verify the extent and direction of interspecific gene flow between C. angustisquama and closely related species to understand the evolutionary process of an extremophyte in solfatara fields. Methods In this study, expressed sequence tag–simple sequence repeat markers were utilized to infer the extent and direction of interspecific gene flow between C. angustisquama and closely related species. Key Results Bayesian clustering and simulation analyses revealed that all individuals of the three hybrid species were classified into the first hybrid generation or first backcross to C. angustisquama; therefore, current interspecific gene flow is limited. Moreover, in the Bayesian inference of historical gene flow based on multispecies samples, the model that assumed no interspecific gene flow was the most strongly supported across all species pairs, including phylogenetically close but ecologically distinctive species pairs. Conclusions Our results revealed that interspecific gene flow between C. angustisquama and its related species has been limited both currently and historically. Moreover, our results of Bayesian inference of historical gene flow indicated that extrinsic, rather than intrinsic, factors probably act as isolating barriers between Carex species, with hybrid breakdown via microhabitat segregation being the probable potential barrier. Overall, our findings provide insights into the evolutionary process of an extremophyte in solfatara fields and offer an important example of the mechanisms of diversification of the speciose genus Carex.

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Regilme, Maria Angenica F., Thaddeus M. Carvajal, Ann–Christin Honnen, Divina M. Amalin e Kozo Watanabe. "The influence of roads on the fine-scale population genetic structure of the dengue vector Aedes aegypti (Linnaeus)". PLOS Neglected Tropical Diseases 15, n.º 2 (26 de fevereiro de 2021): e0009139. http://dx.doi.org/10.1371/journal.pntd.0009139.

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Dengue is endemic in tropical and subtropical countries and is transmitted mainly by Aedes aegypti. Mosquito movement can be affected by human-made structures such as roads that can act as a barrier. Roads can influence the population genetic structure of Ae. aegypti. We investigated the genetic structure and gene flow of Ae. aegypti as influenced by a primary road, España Boulevard (EB) with 2000-meter-long stretch and 24-meters-wide in a very fine spatial scale. We hypothesized that Ae. aegypti populations separated by EB will be different due to the limited gene flow as caused by the barrier effect of the road. A total of 359 adults and 17 larvae Ae. aegypti were collected from June to September 2017 in 13 sites across EB. North (N1-N8) and South (S1-S5) comprised of 211 and 165 individuals, respectively. All mosquitoes were genotyped at 11 microsatellite loci. AMOVA FST indicated significant genetic differentiation across the road. The constructed UPGMA dendrogram found 3 genetic groups revealing the clear separation between North and South sites across the road. On the other hand, Bayesian cluster analysis showed four genetic clusters (K = 4) wherein each individual samples have no distinct genetic cluster thus genetic admixture. Our results suggest that human-made landscape features such as primary roads are potential barriers to mosquito movement thereby limiting its gene flow across the road. This information is valuable in designing an effective mosquito control program in a very fine spatial scale.

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Arenas, Sebastián, Alberto Búrquez, Enriquena Bustamante, Enrique Scheinvar e Luis E. Eguiarte. "Are 150 km of open sea enough? Gene flow and population differentiation in a bat-pollinated columnar cactus". PLOS ONE 18, n.º 6 (29 de junho de 2023): e0282932. http://dx.doi.org/10.1371/journal.pone.0282932.

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Genetic differentiations and phylogeographical patterns are controlled by the interplay between spatial isolation and gene flow. To assess the extent of gene flow across an oceanic barrier, we explored the effect of the separation of the peninsula of Baja California on the evolution of mainland and peninsular populations of the long-lived columnar cactus Stenocereus thurberi. We analyzed twelve populations throughout the OPC distribution range to assess genetic diversity and structure using chloroplast DNA sequences. Genetic diversity was higher (Hd = 0.81), and genetic structure was lower (GST = 0.143) in mainland populations vs peninsular populations (Hd = 0.71, GST = 0.358 respectively). Genetic diversity was negatively associated with elevation but positively with rainfall. Two mainland and one peninsular ancestral haplotypes were reconstructed. Peninsular populations were as isolated among them as with mainland populations. Peninsular haplotypes formed a group with one mainland coastal population, and populations across the gulf shared common haplotypes giving support to regular gene flow across the Gulf. Gene flow is likely mediated by bats, the main pollinators and seed dispersers. Niche modeling suggests that during the Last Glacial Maximum (c. 130 ka), OPC populations shrank to southern locations. Currently, Stenocereus thurberi populations are expanding, and the species is under population divergence despite ongoing gene flow. Ancestral populations are located on the mainland and although vicariant peninsular populations cannot be ruled out, they are likely the result of gene flow across the seemingly formidable barrier of the Gulf of California. Still, unique haplotypes occur in the peninsula and the mainland, and peninsular populations are more structured than those on the mainland.

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Piálek, Jaroslav, e Nick H. Barton. "The Spread of an Advantageous Allele Across a Barrier: The Effects of Random Drift and Selection Against Heterozygotes". Genetics 145, n.º 2 (1 de fevereiro de 1997): 493–504. http://dx.doi.org/10.1093/genetics/145.2.493.

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A local barrier to gene flow will delay the spread of an advantageous allele. Exact calculations for the deterministic case show that an allele that is favorable when rare is delayed very little even by a strong barrier: its spread is slowed by a time proportional to log((B/σ)√2S)/S, where B is the barrier strength, σ the dispersal range, and fitnesses are 1:1 + S:1 + 2S. However,when there is selection against heterozygotes, such that the allele cannot increase from low frequency, a barrier can cause a much greater delay. If gene flow is reduced below a critical value, spread is entirely prevented. Stochastic simulations show that with additive selection, random drift slows down the spread of the allele, below the deterministic speed of σ√2S. The delay to the advance of an advantageous allele caused by a strong barrier can be substantially increased by random drift and increases with B/(2Sρσ2) in a one-dimensional habitat of density ρ. However, with selection against heterozygotes, drift can facilitate the spread and can free an allele that would otherwise be trapped indefinitely by a strong barrier. We discuss the implications of these results for the evolution of chromosome rearrangements.

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Mohan, Ashwini Venkatanarayana, Priyanka Swamy e Kartik Shanker. "Population structure in the Andaman keelback, Xenochrophis tytleri: geographical distance and oceanic barriers to dispersal influence genetic divergence on the Andaman archipelago". PeerJ 6 (9 de outubro de 2018): e5752. http://dx.doi.org/10.7717/peerj.5752.

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Limited gene flow between populations due to geographic distance, presence of barriers or inherent low dispersal ability leads to the formation of genetically structured populations. Strong population structure indicates lowered levels or absence of gene flow which might lead to inbreeding and loss of genetic capacity to recuperate from anthropogenic stress and natural calamities. Terrestrial reptiles are generally known to have low dispersal abilities and few studies have explored drivers of their population structure on continental islands, where both anthropogenic stress and natural calamities are relatively common. We investigated the population structure and drivers of diversification of the Andaman keelback (Xenochrophis tytleri), an endemic, terrestrial and freshwater snake species in the Andaman archipelago, a continental group of islands in the Bay of Bengal. Data was collected from 86 individuals from seven islands and 78 individuals were sequenced for the gene Nuclear Dehydrogenase subunit 4 to identify the number of populations and distribution of genetic diversity across populations. We found 11 haplotypes on seven islands and observed high genetic differentiation between seven populations defined island-wise (FST = 0.82). We further tested the number of populations by incorporating spatial data into Bayesian Clustering Analysis (GENELAND) and identified six populations of the Andaman keelback. We tested for the influence of Isolation-by-distance on these populations. While the overall trend showed a positive correlation between geographic and genetic distance, a correlogram revealed that the positive correlation disappears beyond ∼20–40 km. We also tested for the presence of geographical barriers to gene flow using Monmonier’s algorithm (SPADS), which identified five barriers to dispersal confirming that there are oceanic barriers to dispersal for some island populations of the Andaman keelback. As the Andaman Islands are arranged almost in a straight line from North to South, our data are insufficient to tease apart the roles of geographical distance and barriers to gene flow. We conclude that salt waters between near islands are weak barriers and as the geographical distance between islands increases, so does the strength of the barrier.

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He, Ziwen, Xinnian Li, Ming Yang, Xinfeng Wang, Cairong Zhong, Norman C. Duke, Chung-I. Wu e Suhua Shi. "Speciation with gene flow via cycles of isolation and migration: insights from multiple mangrove taxa". National Science Review 6, n.º 2 (24 de julho de 2018): 275–88. http://dx.doi.org/10.1093/nsr/nwy078.

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AbstractAllopatric speciation requiring an unbroken period of geographical isolation has been the standard model of neo-Darwinism. While doubts have been repeatedly raised, strict allopatry without any gene flow remains a plausible mechanism in most cases. To rigorously reject strict allopatry, genomic sequences superimposed on the geological records of a well-delineated geographical barrier are necessary. The Strait of Malacca, narrowly connecting the Pacific and Indian Ocean coasts, serves at different times either as a geographical barrier or a conduit of gene flow for coastal/marine species. We surveyed 1700 plants from 29 populations of 5 common mangrove species by large-scale DNA sequencing and added several whole-genome assemblies. Speciation between the two oceans is driven by cycles of isolation and gene flow due to the fluctuations in sea level leading to the opening/closing of the Strait to ocean currents. Because the time required for speciation in mangroves is longer than the isolation phases, speciation in these mangroves has proceeded through many cycles of mixing-isolation-mixing, or MIM, cycles. The MIM mechanism, by relaxing the condition of no gene flow, can promote speciation in many more geographical features than strict allopatry can. Finally, the MIM mechanism of speciation is also efficient, potentially yielding mn (m > 1) species after n cycles.

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BARTON, N. H., e M. SHPAK. "The effect of epistasis on the structure of hybrid zones". Genetical Research 75, n.º 2 (abril de 2000): 179–98. http://dx.doi.org/10.1017/s0016672399004334.

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Within hybrid zones that are maintained by a balance between selection and dispersal, linkage disequilibrium is generated by the mixing of divergent populations. This linkage disequilibrium causes selection on each locus to act on all other loci, thereby steepening clines, and generating a barrier to gene flow. Diffusion models predict simple relations between the strength of linkage disequilibrium and the dispersal rate, σ, and between the barrier to gene flow, B, and the reduction in mean fitness, W¯. The aim of this paper is to test the accuracy of these predictions by comparison with an exact deterministic model of unlinked loci (r = 0·5). Disruptive selection acts on the proportion of alleles from the parental populations (p, q): W = exp[−S(4 pq)β], such that the least fit genotype has fitness e−S. Where β [Lt ] 1, fitness is reduced for a wide range of intermediate genotypes; where β [Gt ] 1, fitness is only reduced for those genotypes close to p = 0·5. Even with strong epistasis, linkage disequilibria are close to σ2p′ip′j/ rij, where p′i, p′j are the gradients in allele frequency at loci i, j. The barrier to gene flow, which is reflected in the steepening of neutral clines, is given byformula herewhere r¯, the harmonic mean recombination rate between the neural and selected loci, is here 0·5. This is a close approximation for weak selection, but underestimates B for strong selection. The barrier is stronger for small β, because hybrid fitness is then reduced over a wider range of p. The widths of the selected clines are harder to predict: though simple approximations are accurate for β = 1, they become inaccurate for extreme β because, then, fitness changes sharply with p. Estimates of gene number, made from neutral clines on the assumption that selection acts against heterozygotes, are accurate for weak selection when β = 1; however, for strong selection, gene number is overestimated. For β > 1, gene number is systematically overestimated and, conversely, when β < 1, it is underestimated.

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Johannesson, Kerstin, Zuzanna Zagrodzka, Rui Faria, Anja Marie Westram e Roger K. Butlin. "Is embryo abortion a post‐zygotic barrier to gene flow between Littorina ecotypes?" Journal of Evolutionary Biology 33, n.º 3 (7 de dezembro de 2019): 342–51. http://dx.doi.org/10.1111/jeb.13570.

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Marsh, D. M., R. B. Page, T. J. Hanlon, H. Bareke, R. Corritone, N. Jetter, N. G. Beckman, K. Gardner, D. E. Seifert e P. R. Cabe. "Ecological and genetic evidence that low-order streams inhibit dispersal by red-backed salamanders (Plethodon cinereus)". Canadian Journal of Zoology 85, n.º 3 (fevereiro de 2007): 319–27. http://dx.doi.org/10.1139/z07-008.

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While many studies have examined the barrier effects of large rivers on animal dispersal and gene flow, few studies have considered the barrier effects of small streams. We used displacement experiments and analyses of genetic population structure to examine the effects of first-order and second-order streams on the dispersal of terrestrial red-backed salamanders, Plethodon cinereus (Green, 1818). We marked red-backed salamanders from near the edges of one first-order stream and one second-order stream, and experimentally displaced them either across the stream or an equal distance farther into the forest. A comparison of return rates indicated that both streams were partial barriers to salamander movement, reducing return rates by approximately 50%. Analysis of six microsatellite loci from paired plots on the same side and on opposite sides of the second-order stream suggested that the stream did contribute to genetic differentiation of salamander populations. Collectively, our results imply that low-order streams do influence patterns of movement and gene flow in red-backed salamanders. We suggest that given the high density of first-order and second-order streams in most landscapes, these features may have important effects on species that, like red-backed salamanders, have limited dispersal and large geographic ranges.

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Skroblin, Anja, Robert Lanfear, Andrew Cockburn e Sarah Legge. "Inferring population connectivity across the range of the purple-crowned fairy-wren (Malurus coronatus) from mitochondrial DNA and morphology: implications for conservation management". Australian Journal of Zoology 60, n.º 3 (2012): 199. http://dx.doi.org/10.1071/zo12093.

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Knowledge of population structure and patterns of connectivity is required to implement effective conservation measures for the purple-crowned fairy-wren (Malurus coronatus), a threatened endemic of northern Australia. This study aimed to identify barriers to dispersal across the distribution of M. coronatus, investigate the impact that the recent declines may have on population connectivity, and propose conservation actions to maintain natural patterns of gene flow. Analysis of mitochondrial DNA sequences from 87 M. coronatus identified two phylogenetic clusters that corresponded with the phenotypically defined western (M. c. coronatus) and eastern (M. c. macgillivrayi) subspecies. The genetic divergence between these subspecies was consistent with isolation by a natural barrier to gene flow, and supports their separate conservation management. Within the declining M. c. coronatus, the lack of genetic divergence and only slight morphological difference between remnant populations indicates that populations were recently linked by gene flow. It is likely that widespread habitat degradation and the recent extirpation of M. c. coronatus from the Ord River will disrupt connectivity between, and dynamics within, remnant populations. To prevent further declines, conservation of M. coronatus must preserve areas of quality habitat and restore connectivity between isolated populations.

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Knight, James T., Catherine J. Nock, Martin S. Elphinstone e Peter R. Baverstock. "Conservation implications of distinct genetic structuring in the endangered freshwater fish Nannoperca oxleyana (Percichthyidae)". Marine and Freshwater Research 60, n.º 1 (2009): 34. http://dx.doi.org/10.1071/mf08022.

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The maintenance of genetic diversity and gene flow in threatened species is a vital consideration for recovery programs. The endangered Oxleyan pygmy perch Nannoperca oxleyana has a fragmented distribution within coastal freshwater drainages of southern Queensland and northern New South Wales, Australia. In the present study, mitochondrial DNA control region variation was used to assess genetic diversity and structure across the geographical range of this species. Haplotypic diversity was highest in a small NSW subcatchment south of Evans Head (h = 0.594) followed by Marcus Creek in Queensland (h = 0.475). Distinct genetic differentiation was evident among the Queensland localities and the NSW subcatchments, implying restricted gene flow between coastal river systems. One of the nine haplotypes detected was distributed over 83.4% of the species’ range, suggesting historical connectivity among the now fragmented populations. These patterns were concordant with eustatic changes associated with the last glacial maximum. High barrier sand dunes may also act as barriers to gene flow and dispersal between adjacent NSW subcatchments. Conservation efforts should focus on the preservation of genetic diversity by maintaining as many genetically differentiated populations as possible. The relatively diverse populations inhabiting the South Evans Head subcatchment and Marcus Creek require special management consideration.

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Curley, Colleen T., Brian P. Mead, Karina Negron, Namho Kim, William J. Garrison, G. Wilson Miller, Kathryn M. Kingsmore et al. "Augmentation of brain tumor interstitial flow via focused ultrasound promotes brain-penetrating nanoparticle dispersion and transfection". Science Advances 6, n.º 18 (maio de 2020): eaay1344. http://dx.doi.org/10.1126/sciadv.aay1344.

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The delivery of systemically administered gene therapies to brain tumors is exceptionally difficult because of the blood-brain barrier (BBB) and blood-tumor barrier (BTB). In addition, the adhesive and nanoporous tumor extracellular matrix hinders therapeutic dispersion. We first developed the use of magnetic resonance image (MRI)–guided focused ultrasound (FUS) and microbubbles as a platform approach for transfecting brain tumors by targeting the delivery of systemically administered “brain-penetrating” nanoparticle (BPN) gene vectors across the BTB/BBB. Next, using an MRI-based transport analysis, we determined that after FUS-mediated BTB/BBB opening, mean interstitial flow velocity magnitude doubled, with “per voxel” flow directions changing by an average of ~70° to 80°. Last, we observed that FUS-mediated BTB/BBB opening increased the dispersion of directly injected BPNs through tumor tissue by >100%. We conclude that FUS-mediated BTB/BBB opening yields markedly augmented interstitial tumor flow that, in turn, plays a critical role in enhancing BPN transport through tumor tissue.

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Richmond, Jonathan Q., e Elizabeth L. Jockusch. "Body size evolution simultaneously creates and collapses species boundaries in a clade of scincid lizards". Proceedings of the Royal Society B: Biological Sciences 274, n.º 1619 (8 de maio de 2007): 1701–8. http://dx.doi.org/10.1098/rspb.2007.0364.

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Speciation is generally viewed as an irreversible process, although habitat alterations can erase reproductive barriers if divergence between ecologically differentiated species is recent. Reversed speciation might also occur if geographical contact is established between species that have evolved the same reproductive isolating barrier in parallel. Here, we demonstrate a loss of intrinsic reproductive isolation in a clade of scincid lizards as a result of parallel body size evolution, which has allowed for gene flow where large-bodied lineages are in secondary contact. An mtDNA phylogeny confirms the monophyly of the Plestiodon skiltonianus species complex, but rejects that of two size-differentiated ecomorphs. Mate compatibility experiments show that the high degree of body size divergence imposes a strong reproductive barrier between the two morphs; however, the strength of the barrier is greatly diminished between parallel-evolved forms. Since two large-bodied lineages are in geographical contact in the Sierra Nevada Mountains of California, we were also able to test for postzygotic isolation under natural conditions. Analyses of amplified fragment length polymorphisms show that extensive gene exchange is occurring across the contact zone, resulting in an overall pattern consistent with isolation by distance. These results provide evidence of reversed speciation between clades that diverged from a common ancestor more than 12 Myr ago.

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BIERNE, NICOLAS, THOMAS LENORMAND, FRANÇOIS BONHOMME e PATRICE DAVID. "Deleterious mutations in a hybrid zone: can mutational load decrease the barrier to gene flow?" Genetical Research 80, n.º 3 (dezembro de 2002): 197–204. http://dx.doi.org/10.1017/s001667230200592x.

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The aim of this paper is to investigate the effect of deleterious mutations in a hybrid zone maintained by selection against hybrids. In such zones, linkage disequilibria among hybrid depression loci, resulting from a balance between migration and selection, are crucial in maintaining the barrier because they allow each locus, in addition to its own selection coefficient, to cumulate indirect selective effects from other loci. Deleterious alleles produce heterosis and increase by this means the effective migration rate in structured populations. In a hybrid zone, they therefore contribute to decrease linkage disequilibria as well as the barrier to gene flow imposed by hybrid depression. However, deleterious mutations have no effect: (i) when selection against hybrids is weak, because linkage disequilibria are small even without heterosis in this case, or (ii) when selection against hybrids is so strong that it overwhelms heterosis. On the other hand, with moderate selection against hybrids, the decrease in the strength of the barrier due to heterosis may reach detectable levels, although it requires relatively small population sizes and/or migration rates. The effect is expected to be small and only within small genomes where loci are tightly linked can it become strong. Nevertheless, neglecting mutational load may to some extent obscure the estimations of selective parameters based either on artificial F1 crosses or on cline characteristics.

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Rieseberg, Loren H., Jeannette Whitton e Keith Gardner. "Hybrid Zones and the Genetic Architecture of a Barrier to Gene Flow Between Two Sunflower Species". Genetics 152, n.º 2 (1 de junho de 1999): 713–27. http://dx.doi.org/10.1093/genetics/152.2.713.

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Abstract Genetic analyses of reproductive barriers represent one of the few methods by which theories of speciation can be tested. However, genetic study is often restricted to model organisms that have short generation times and are easily propagated in the laboratory. Replicate hybrid zones with a diversity of recombinant genotypes of varying age offer increased resolution for genetic mapping experiments and expand the pool of organisms amenable to genetic study. Using 88 markers distributed across 17 chromosomes, we analyze the introgression of chromosomal segments of Helianthus petiolaris into H. annuus in three natural hybrid zones. Introgression was significantly reduced relative to neutral expectations for 26 chromosomal segments, suggesting that each segment contains one or more factors that contribute to isolation. Pollen sterility is significantly associated with 16 of these 26 segments, providing a straightforward explanation of why this subset of blocks is disadvantageous in hybrids. In addition, comparison of rates of introgression across colinear vs. rearranged chromosomes indicates that close to 50% of the barrier to introgression is due to chromosomal rearrangements. These results demonstrate the utility of hybrid zones for identifying factors contributing to isolation and verify the prediction of increased resolution relative to controlled crosses.

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Cowman, Peter F., e David R. Bellwood. "Vicariance across major marine biogeographic barriers: temporal concordance and the relative intensity of hard versus soft barriers". Proceedings of the Royal Society B: Biological Sciences 280, n.º 1768 (7 de outubro de 2013): 20131541. http://dx.doi.org/10.1098/rspb.2013.1541.

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The marine tropics contain five major biogeographic regions (East Pacific, Atlantic, Indian Ocean, Indo-Australian Archipelago (IAA) and Central Pacific). These regions are separated by both hard and soft barriers. Reconstructing ancestral vicariance, we evaluate the extent of temporal concordance in vicariance events across three major barriers (Terminal Tethyan Event (TTE), Isthmus of Panama (IOP), East Pacific Barrier, EPB) and two incomplete barriers (either side of the IAA) for the Labridae, Pomacentridae and Chaetodontidae. We found a marked lack of temporal congruence within and among the three fish families in vicariance events associated with the EPB, TTE and IOP. Vicariance across hard barriers separating the Atlantic and Indo-Pacific (TTE, IOP) is temporally diffuse, with many vicariance events preceding barrier formation. In marked contrast, soft barriers either side of the IAA hotspot support tightly concordant vicariance events (2.5 Myr on Indian Ocean side; 6 Myr on Central Pacific side). Temporal concordance in vicariance points to large-scale temporally restricted gene flow during the Late Miocene and Pliocene. Despite different and often complex histories, both hard and soft barriers have comparably strong effects on the evolution of coral reef taxa.

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Loretán, Gisela, Eva Carolina Rueda, Juan Manuel Cabrera, Marcos Pérez-Losada, Pablo Agustín Collins e Federico Giri. "Geographical isolation and restricted gene flow drive speciation of Aegla singularis (Decapoda: Anomura: Aeglidae) in southern South America". Biological Journal of the Linnean Society 129, n.º 1 (18 de novembro de 2019): 177–89. http://dx.doi.org/10.1093/biolinnean/blz148.

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Abstract Geographical isolation is a key element in allopatric speciation. If gene flow is interrupted for long enough by geographical barriers, populations can evolve independently and eventually form distinct species. Aegla singularis provides an ideal model to study this process due to the characteristics of the geographical area that it occupies and its limited dispersal ability. Aegla singularis inhabits streams of the Uruguay and Paraná River basins in the Neotropical region of South America. The basins are separated by the Sierra Central Mountains. Here we studied the speciation of A. singularis resulting from geographical isolation by using molecular and morphometric data. Individuals of A. singularis were analysed using geometric morphometrics and genetic data (COII and EFα1). We found significant differences in shape and genetics between A. singularis populations from the two basins. These differences suggest ongoing divergence due to restricted gene flow caused by the geographical barrier of the Sierra Central Mountains, indicating that the populations of the Parana and Uruguay River slopes are undergoing divergence.

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Whitton, Jeannette, Katrina M. Dlugosch e Christopher J. Sears. "Molecular and morphological evidence for and against gene flow in sympatric apomicts of the North American Crepis agamic complex (Asteraceae)This paper is one of a selection of papers published in the Special Issue on Systematics Research." Botany 86, n.º 8 (agosto de 2008): 877–85. http://dx.doi.org/10.1139/b08-071.

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The study of sympatric populations of closely related plant species often reveals evidence of hybridization. Mechanisms that reduce outcrossing (e.g., selfing, apomixis) may allow co-occurrence without gene flow. In this study, we describe patterns of genetic variation in two contact zones, each comprising three closely related morphological types, that key to three distinct species in the North American Crepis agamic (apomictic) complex. We used RAPD markers to characterize individuals from two sites: one in northern California (Sardine Lookout) and another in northwestern Oregon (Summit Road). At Sardine Lookout, we discerned a total of four multilocus genotypes, two in one species, and one each in the other two species. Our findings suggest that distinct morphological types are maintained by absolute barriers to gene flow at this site. At Summit Road, we found greater genotypic diversity, with a total of 24 genotypes across 30 individuals. One of the morphological types was clearly genetically differentiated from the other two, with no variable markers shared with other species at this site. The two remaining species showed evidence of gene flow, with no unique markers discerning them. Morphological data tend to support this conclusion, with univariate and multivariate analyses indicating a pattern of variation spanning the two species. Taken together, these patterns suggest that contact zones need not represent hybrid zones, and that apomixis can serve as an effective barrier to gene flow that may allow for stable coexistence of close relatives.

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Manawaduge, Chapa G., Anthony R. Clarke e David A. Hurwood. "Divergent east-west lineages in an Australian fruit fly, (Bactrocera jarvisi), associated with the Carpentaria Basin divide". PLOS ONE 18, n.º 6 (2 de junho de 2023): e0276247. http://dx.doi.org/10.1371/journal.pone.0276247.

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Bactrocera jarvisi is an endemic Australian fruit fly species (Diptera: Tephritidae). It occurs commonly across tropical and subtropical coastal Australia, from far-northern Western Australia, across the ‘Top End’ of the Northern Territory, and then down the Queensland east coast. Across this range, its distribution crosses several well documented biogeographic barriers. In order to better understand factors leading to the divergence of Australian fruit fly lineages, we carried out a population genetic study of B. jarvisi from across its range using genome-wide SNP analysis, utilising adult specimens gained from trapping and fruit rearing. Populations from the Northern Territory (NT) and Western Australia were genetically similar to each other, but divergent from the genetically uniform east-coast (= Queensland, QLD) population. Phylogenetic analysis demonstrated that the NT population derived from the QLD population. We infer a role for the Carpentaria Basin as a biogeographic barrier restricting east-west gene flow. The QLD populations were largely panmictic and recognised east-coast biogeographic barriers play no part in north-south population structuring. While the NT and QLD populations were genetically distinct, there was evidence for the historically recent translocation of flies from each region to the other. Flies reared from different host fruits collected in the same location showed no genetic divergence. While a role for the Carpentaria Basin as a barrier to gene flow for Australian fruit flies agrees with existing work on the related B. tryoni, the reason(s) for population panmixia for B. jarvisi (and B. tryoni) over the entire Queensland east coast, a linear north-south distance of >2000km, remains unknown.

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Richards, Thomas J., e Daniel Ortiz-Barrientos. "Immigrant inviability produces a strong barrier to gene flow between parapatric ecotypes ofSenecio lautus". Evolution 70, n.º 6 (30 de maio de 2016): 1239–48. http://dx.doi.org/10.1111/evo.12936.

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Baums, Iliana B., Jennifer N. Boulay, Nicholas R. Polato e Michael E. Hellberg. "No gene flow across the Eastern Pacific Barrier in the reef-building coralPorites lobata". Molecular Ecology 21, n.º 22 (3 de setembro de 2012): 5418–33. http://dx.doi.org/10.1111/j.1365-294x.2012.05733.x.

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Sá-Pinto, A., M. Martínez-Fernández, C. López-Fernández, Z. Ferreira, R. Pereira, J. Gosálvez e E. Rolán-Alvarez. "Incipient post-zygotic barrier in a model system of ecological speciation with gene flow". Journal of Evolutionary Biology 26, n.º 12 (29 de outubro de 2013): 2750–56. http://dx.doi.org/10.1111/jeb.12269.

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Liu, Yongbo, Fajun Chen, Xiao Guan e Junsheng Li. "High crop barrier reduces gene flow from transgenic to conventional maize in large fields". European Journal of Agronomy 71 (novembro de 2015): 135–40. http://dx.doi.org/10.1016/j.eja.2015.09.005.

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Santa-Maria, Ana R., Fruzsina R. Walter, Ricardo Figueiredo, András Kincses, Judit P. Vigh, Marjolein Heymans, Maxime Culot et al. "Flow induces barrier and glycocalyx-related genes and negative surface charge in a lab-on-a-chip human blood-brain barrier model". Journal of Cerebral Blood Flow & Metabolism 41, n.º 9 (9 de fevereiro de 2021): 2201–15. http://dx.doi.org/10.1177/0271678x21992638.

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Microfluidic lab-on-a-chip (LOC) devices allow the study of blood-brain barrier (BBB) properties in dynamic conditions. We studied a BBB model, consisting of human endothelial cells derived from hematopoietic stem cells in co-culture with brain pericytes, in an LOC device to study fluid flow in the regulation of endothelial, BBB and glycocalyx-related genes and surface charge. The highly negatively charged endothelial surface glycocalyx functions as mechano-sensor detecting shear forces generated by blood flow on the luminal side of brain endothelial cells and contributes to the physical barrier of the BBB. Despite the importance of glycocalyx in the regulation of BBB permeability in physiological conditions and in diseases, the underlying mechanisms remained unclear. The MACE-seq gene expression profiling analysis showed differentially expressed endothelial, BBB and glycocalyx core protein genes after fluid flow, as well as enriched pathways for the extracellular matrix molecules. We observed increased barrier properties, a higher intensity glycocalyx staining and a more negative surface charge of human brain-like endothelial cells (BLECs) in dynamic conditions. Our work is the first study to provide data on BBB properties and glycocalyx of BLECs in an LOC device under dynamic conditions and confirms the importance of fluid flow for BBB culture models.

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Viard, Frédérique, Cynthia Riginos e Nicolas Bierne. "Anthropogenic hybridization at sea: three evolutionary questions relevant to invasive species management". Philosophical Transactions of the Royal Society B: Biological Sciences 375, n.º 1806 (13 de julho de 2020): 20190547. http://dx.doi.org/10.1098/rstb.2019.0547.

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Species introductions promote secondary contacts between taxa with long histories of allopatric divergence. Anthropogenic contact zones thus offer valuable contrasts to speciation studies in natural systems where past spatial isolations may have been brief or intermittent. Investigations of anthropogenic hybridization are rare for marine animals, which have high fecundity and high dispersal ability, characteristics that contrast to most terrestrial animals. Genomic studies indicate that gene flow can still occur after millions of years of divergence, as illustrated by invasive mussels and tunicates. In this context, we highlight three issues: (i) the effects of high propagule pressure and demographic asymmetries on introgression directionality, (ii) the role of hybridization in preventing introduced species spread, and (iii) the importance of postzygotic barriers in maintaining reproductive isolation. Anthropogenic contact zones offer evolutionary biologists unprecedented large scale hybridization experiments. In addition to breaking the highly effective reproductive isolating barrier of spatial segregation, they allow researchers to explore unusual demographic contexts with strong asymmetries. The outcomes are diverse, from introgression swamping to strong barriers to gene flow, and lead to local containment or widespread invasion. These outcomes should not be neglected in management policies of marine invasive species. This article is part of the theme issue ‘Towards the completion of speciation: the evolution of reproductive isolation beyond the first barriers’.

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Santos, Ronaldo Pereira, Paula Cristina da Silva Ângelo, Paulo de Tarso Barbosa Sampaio, Regina Caetano Quisen, Ângela Maria Conte Leite e Cristiane Lopes de Oliveira. "Geographic pattern of genetic diversity in natural populations of Rosewood (Aniba rosaeodora), in the Central Amazonia". Acta Amazonica 38, n.º 3 (2008): 459–66. http://dx.doi.org/10.1590/s0044-59672008000300010.

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Rosewood (Aniba rosaeodora Ducke, Lauraceae) is an Amazonian evergreen tree and a source of the purest linalool, the main component of its essential oil, which is very valuable in the international perfumery market. After decades of over-exploitation it is currently considered as threatened. We evaluated the genetic diversity and its distribution in four populations in Central Amazonia. Thirty-five reliable RAPD markers were generated, of which 32 were polymorphic (91.4%). Variation was higher within the populations (76.5%; p < 0.0001) and geographic distribution contributed to population differentiation (23.4%; p < 0.0001). The Amazon River had a small influence on gene flow (3.3%; p < 0.0001), but we identified evidence of gene flow across the river. There were significant differences in marker frequencies (p < 0.05), in agreement with the low gene flow (Nm = 2.02). The correlation between genetic distance and gene flow was - 0.95 (p = 0.06) and between geographic distance and gene flow was -0.78 (p = 0.12). There was a geographic cline of variability across an East-West axis, influenced as well by the Amazon River, suggesting the river could be a barrier to gene flow. Although threatened, these Rosewood populations retain high diversity, with the highest levels in the Manaus population, which has been protected for over 42 years in a Reserve.

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