scholarly journals Endosperm-based hybridization barriers explain the pattern of gene flow between Arabidopsis lyrata and Arabidopsis arenosa in Central Europe

2017 ◽  
Vol 114 (6) ◽  
pp. E1027-E1035 ◽  
Author(s):  
Clément Lafon-Placette ◽  
Ida M. Johannessen ◽  
Karina S. Hornslien ◽  
Mohammad F. Ali ◽  
Katrine N. Bjerkan ◽  
...  
Keyword(s):  
Gene Flow ◽  
Central Europe ◽  
Diploid Species ◽  
Biological Species ◽  
Biological Species Concept ◽  
Interspecific Gene Flow ◽  
Seed Formation ◽  
Arabidopsis Lyrata ◽  
Hybrid Seeds ◽  
Arabidopsis Arenosa

Based on the biological species concept, two species are considered distinct if reproductive barriers prevent gene flow between them. In Central Europe, the diploid species Arabidopsis lyrata and Arabidopsis arenosa are genetically isolated, thus fitting this concept as “good species.” Nonetheless, interspecific gene flow involving their tetraploid forms has been described. The reasons for this ploidy-dependent reproductive isolation remain unknown. Here, we show that hybridization between diploid A. lyrata and A. arenosa causes mainly inviable seed formation, revealing a strong postzygotic reproductive barrier separating these two species. Although viability of hybrid seeds was impaired in both directions of hybridization, the cause for seed arrest differed. Hybridization of A. lyrata seed parents with A. arenosa pollen donors resulted in failure of endosperm cellularization, whereas the endosperm of reciprocal hybrids cellularized precociously. Endosperm cellularization failure in both hybridization directions is likely causal for the embryo arrest. Importantly, natural tetraploid A. lyrata was able to form viable hybrid seeds with diploid and tetraploid A. arenosa, associated with the reestablishment of normal endosperm cellularization. Conversely, the defects of hybrid seeds between tetraploid A. arenosa and diploid A. lyrata were aggravated. According to these results, we hypothesize that a tetraploidization event in A. lyrata allowed the production of viable hybrid seeds with A. arenosa, enabling gene flow between the two species.

scholarly journals Genes and speciation: is it time to abandon the biological species concept?

2019 ◽  
Vol 7 (8) ◽  
pp. 1387-1397 ◽  
Author(s):  
Xinfeng Wang ◽  
Ziwen He ◽  
Suhua Shi ◽  
Chung-I Wu
Keyword(s):  
Gene Flow ◽  
Species Concept ◽  
Biological Species ◽  
Biological Species Concept ◽  
Geographical Isolation ◽  
Fundamental Nature ◽  
Genomic Analyses ◽  
Number Of Genes ◽  
The Common ◽  
Common Perception

Abstract The biological species concept (BSC) is the cornerstone of neo-Darwinian thinking. In BSC, species do not exchange genes either during or after speciation. However, as gene flow during speciation is increasingly being reported in a substantial literature, it seems time to reassess the revered, but often doubted, BSC. Contrary to the common perception, BSC should expect substantial gene flow at the onset of speciation, not least because geographical isolation develops gradually. Although BSC does not stipulate how speciation begins, it does require a sustained period of isolation for speciation to complete its course. Evidence against BSC must demonstrate that the observed gene flow does not merely occur at the onset of speciation but continues until its completion. Importantly, recent genomic analyses cannot reject this more realistic version of BSC, although future analyses may still prove it wrong. The ultimate acceptance or rejection of BSC is not merely about a historical debate; rather, it is about the fundamental nature of species – are species (and, hence, divergent adaptations) driven by a relatively small number of genes, or by thousands of them? Many levels of biology, ranging from taxonomy to biodiversity, depend on this resolution.

scholarly journals An overview of speciation and species limits in birds

The Auk ◽  
2021 ◽  
Author(s):  
Kevin Winker
Keyword(s):  
Gene Flow ◽  
Integrative Taxonomy ◽  
Difficult Problem ◽  
Biological Species ◽  
Biological Species Concept ◽  
Species Limits ◽  
Main Driver ◽  
Data Signal ◽  
Clear Line ◽  
Silver Bullet

Abstract Accurately determining avian species limits has been a challenge and a work in progress for most of a century. It is a fascinating but difficult problem. Under the biological species concept, only lineages that remain essentially independent when they are in sympatry are clearly species. Otherwise, there is no clear line yet found that marks when a pair of diverging lineages (e.g., in allopatry) become different enough to warrant full biological species status. Also, with more data, species limits often require reevaluation. The process of divergence and speciation is itself very complex and is the focus of intense research. Translating what we understand of that process into taxonomic names can be challenging. A series of issues are important. Single-locus criteria are unlikely to be convincing. Genetic independence is not a species limits requirement, but the degree of independence (gene flow) needs to be considered when there is opportunity for gene flow and independence is not complete. Time-based species (limits determined by time of separation) are unsatisfactory, though integrating time more effectively into our datasets is warranted. We need to disentangle data signal due to neutral processes vs. selection and prioritize the latter as the main driver of speciation. Assortative mating is also not likely to be an adequate criterion for determining species limits. Hybridization and gene flow are more important than ever, and there is a condition not being treated evenly in taxonomy: evolutionary trysts of 2 or more lineages stuck together through gene flow just short of speciation over long periods. Comparative methods that use what occurs between good species in contact to infer species limits among allopatric forms remain the gold standard, but they can be inaccurate and controversial. Species-level taxonomy in birds is likely to remain unsettled for some time. While the study of avian speciation has never been more exciting and dynamic, there is no silver bullet for species delimitation, nor is it likely that there will ever be one. Careful work using integrative taxonomy in a comparative framework is the most promising way forward.

scholarly journals Interspecific Hybridization of Fragaria vesca subspecies with F. nilgerrensis, F. nubicola, F. pentaphylla, and F. viridis

2005 ◽  
Vol 130 (3) ◽  
pp. 418-423 ◽  
Author(s):  
R.H. Bors ◽  
J.A. Sullivan
Keyword(s):  
Gene Flow ◽  
Interspecific Hybridization ◽  
North American ◽  
Diploid Species ◽  
Fragaria Vesca ◽  
Strong Potential ◽  
Hybrid Seeds ◽  
Bridge Species

The potential of using Fragaria vesca L. as a bridge species for interspecific hybridization to F. nilgerrensis Schlect, F. nubicola Lindl., F. pentaphylla Losinsk, and F. viridis Duch. was investigated using a wide germplasm base of 40 F. vesca accessions. This study was successful in producing many hybrids between F. vesca and other diploid species indicating its value as a bridge species. Of the species used as males, F. nubicola, F. pentaphylla, and F. viridis accessions were more successful, averaging 8 to 16 fruit and 16 to 25 seeds/fruit. It was most difficult to obtain hybrids with F. nilgerrensis, which had only three seeds per fruit. Differences among pollen donors were minimal when hybrid seeds were germinated in vitro. For different species combinations, 75% to 99% of seeds had embryos and 77% to 89% of these embryos germinated. The lack of significant differences in crossability variables among the four F. vesca subspecies [i.e., ssp. americana (Porter) Staudt, ssp. bracteata (Heller) Staudt, ssp. vesca L., and ssp. vesca var. semper-florens L.] demonstrated the similarity between these species and the strong potential for gene flow between F. vesca and other diploid species. As European and North American F. vesca subspecies are not sufficiently divergent to differ in interspecific hybridization, F. vesca may be a younger species rather than an older progenitor species.

scholarly journals Sympatric and allopatric differentiation delineates population structure in free-living terrestrial bacteria

2019 ◽  
Author(s):  
Alexander B. Chase ◽  
Philip Arevalo ◽  
Eoin L. Brodie ◽  
Martin F. Polz ◽  
Ulas Karaoz ◽  
...  
Keyword(s):  
Gene Flow ◽  
Isolation By Distance ◽  
Biological Species ◽  
Microbial Populations ◽  
Marker Genes ◽  
Rrna Gene ◽  
Biological Species Concept ◽  
Free Living ◽  
Species Definition ◽  
Isolation By Environment

ABSTRACTIn free-living bacteria and archaea, the equivalent of the biological species concept does not exist, creating several barriers to the study of the processes contributing to microbial diversification. As such, microorganisms are often operationally defined using conserved marker genes (i.e., 16S rRNA gene) or whole-genome measurements (i.e., ANI) to interpret intra-specific processes. However, as in eukaryotes, investigations into microbial populations must consider the potential for interacting genotypes among individuals that are subjected to similar environmental selective pressures. Therefore, we isolated 26 strains within a single bacterial ecotype (equivalent to a eukaryotic species definition) from a common habitat (leaf litter) across a regional climate gradient and asked whether the genetic diversity in a free-living soil bacterium (Curtobacterium) was consistent with patterns of allopatric or sympatric differentiation. By examining patterns of gene flow, our results indicate that microbial populations are delineated by gene flow discontinuities and exhibit evidence for population-specific adaptation. We conclude that the genetic structure within this bacterium is due to both adaptation within localized microenvironments (isolation-by-environment) as well as dispersal limitation between geographic locations (isolation-by-distance).

scholarly journals Hybridization without guilt: gene flow and the biological species concept

2001 ◽  
Vol 14 (6) ◽  
pp. 868-869 ◽  
Author(s):  
H. D. Rundle ◽  
F. Breden ◽  
C. Griswold ◽  
A. ��. Mooers ◽  
R. A. Vos ◽  
...  
Keyword(s):  
Gene Flow ◽  
Species Concept ◽  
Biological Species ◽  
Biological Species Concept

scholarly journals Biological species in the viral world

2018 ◽  
Vol 115 (23) ◽  
pp. 6040-6045 ◽  
Author(s):  
Louis-Marie Bobay ◽  
Howard Ochman
Keyword(s):  
Gene Flow ◽  
Species Concept ◽  
Genome Structure ◽  
Biological Species ◽  
Arbitrary Sequence ◽  
Biological Species Concept ◽  
Host Tropism ◽  
Universal Definition ◽  
Definition Of ◽  
Shared Gene

Due to their dependence on cellular organisms for metabolism and replication, viruses are typically named and assigned to species according to their genome structure and the original host that they infect. But because viruses often infect multiple hosts and the numbers of distinct lineages within a host can be vast, their delineation into species is often dictated by arbitrary sequence thresholds, which are highly inconsistent across lineages. Here we apply an approach to determine the boundaries of viral species based on the detection of gene flow within populations, thereby defining viral species according to the biological species concept (BSC). Despite the potential for gene transfer between highly divergent genomes, viruses, like the cellular organisms they infect, assort into reproductively isolated groups and can be organized into biological species. This approach revealed that BSC-defined viral species are often congruent with the taxonomic partitioning based on shared gene contents and host tropism, and that bacteriophages can similarly be classified in biological species. These results open the possibility to use a single, universal definition of species that is applicable across cellular and acellular lifeforms.

scholarly journals The rate of evolution of postmating-prezygotic reproductive isolation in Drosophila

2017 ◽  
Author(s):  
David A. Turissini ◽  
Joseph A. McGirr ◽  
Sonali S. Patel ◽  
Jean R. David ◽  
Daniel R. Matute
Keyword(s):  
Gene Flow ◽  
Reproductive Isolation ◽  
Hybrid Sterility ◽  
Biological Species ◽  
Biological Species Concept ◽  
Premating Isolation ◽  
Hybrid Inviability ◽  
Systematic Analysis ◽  
Rates Of Evolution ◽  
Postzygotic Barriers

ABSTRACTReproductive isolation (RI) is an intrinsic aspect of species, as described in the Biological Species Concept. For that reason, the identification of the precise traits and mechanisms of RI, and the rates at which they evolve, is crucial to understanding how species originate and persist. Nonetheless, precise measurements of the magnitude of reproductive isolation are rare. Previous work has measured the rates of evolution of prezygotic and postzygotic barriers to gene flow, yet no systematic analysis has carried out the study of the rates of evolution of postmating-prezygotic (PMPZ) barriers. We systematically measured the magnitude of two barriers to gene flow that act after mating occurs but before zygotic fertilization and also measured a premating (female mating rate in nonchoice experiments) and two postzygotic barriers (hybrid inviability and hybrid sterility) for all pairwise crosses of species within the Drosophila melanogaster subgroup. Our results indicate that PMPZ isolation evolves faster than hybrid inviability but slower than premating isolation. We also describe seven new interspecific hybrids in the group. Our findings open up a large repertoire of tools that will enable researchers to manipulate hybrids and explore the genetic basis of interspecific differentiation, reproductive isolation, and speciation.

scholarly journals Parthenogenesis as a solution to hybrid sterility: the mechanistic basis of meiotic distortions in clonal and sterile hybrids

2019 ◽  
Author(s):  
Dmitrij Dedukh ◽  
Zuzana Majtánová ◽  
Anatolie Marta ◽  
Martin Pšenička ◽  
Jan Kotusz ◽  
...  
Keyword(s):  
Gene Flow ◽  
Molecular Mechanisms ◽  
Hybrid Sterility ◽  
Biological Species ◽  
Female Fertility ◽  
Interspecific Gene Flow ◽  
General Validity ◽  
Specific Manner ◽  
Postzygotic Barriers ◽  
Mechanistic Basis

AbstractFormation of species generally occurs in a continuum from potentially intermixing populations to independent entities isolated from other species by pre- and postzygotic barriers. Especially the establishment of hybrid sterility (HS) is a hallmark of speciation, which usually emerges at different rates between hybrid sexes. However, although HS is frequently observed, the underlying molecular mechanisms remain poorly understood. Here we report that speciation proceeds through a previously unnoticed stage at which gene flow is completely interrupted on side of both hybrid’s sexes, although only male hybrids are sterile, while female fertility is rescued due to a particular gametogenetic deviation leading to the formation of clonal gametes. Specifically, analysis of gametogenetic pathways in hybrids between fish species Cobitis elongatoides and C. taenia revealed that male HS resulted from extensive asynapses and crossover reduction among elongatoides-taenia chromosomal pairs followed by apoptosis. By contrast, hybrid females exhibited premeiotic genome endoreplication which ensured proper formation of bivalents between identical chromosomal copies. This deviation ultimately restored fertility in females but since it simultaneously leads to the production of unreduced clonal gametes, it restricts interspecific gene flow thereby directly contributing to speciation. In conclusion, our data demonstrate that the emergence of asexuality may remedy HS in a sex-specific manner and is intermingled with the speciation process. Although gametogenetic mechanisms employed by asexual animals and plants have rarely been scrutinized, available evidence suggests that premeiotic endoreplication is relatively widespread. This suggests that observed link between HS and clonality may have general validity in taxa able of asexual reproduction.Author’s summarySpecies are fundamental evolutionary units that presumably evolve in a continuum from potentially intermixing populations to independent entities isolated from other species by pre- and postzygotic barriers. Especially the establishment of hybrid sterility (HS) is a hallmark of speciation, which usually emerges at different rates between hybrid sexes. However, although HS is frequently observed, the underlying molecular mechanisms remain poorly understood. Here we report the existence of a previously unnoticed stage of speciation at which gene flow is completely interrupted, although only male hybrids are sterile, while female fertility is rescued due to a particular gametogenetic deviation leading to formation of clonal gametes. Specifically, HS resulted from extensive asynapses in male gonads, but in females the hybridization provoked premeiotic endoreplication which rescued chromosome pairing and fertility. Simultaneously, this meiotic deviation caused clonal transmission of maternal genome, thereby effectively restricting the interspeficic gene flow. Our results emphasize that emergence of clonality is a type of hybrid incompatibility that is intermingled with the formation of biological species and may remedy hybrid sterility in a sex-specific manner.

scholarly journals Toward understanding the genetic mechanisms of speciation: Fine-grained introgressions between species

2020 ◽  
Author(s):  
Xinfeng Wang ◽  
Zixiao Guo ◽  
Shaohua Xu ◽  
Shao Shao ◽  
Sen Li ◽  
...  
Keyword(s):  
Gene Flow ◽  
De Novo ◽  
Biological Species ◽  
Adaptive Divergence ◽  
Biological Species Concept ◽  
Extensive Literature ◽  
Mangrove Species ◽  
Fine Grained ◽  
Genetic Mechanisms ◽  
Definition Of

Abstract The biological species concept (BSC) is the prevailing definition of species whereby genes cannot be exchanged during or after speciation. In contrast, since only genes that contribute to the adaptive divergence between species should be non-exchangeable, BSC appears to bear little relationship to the genetic process of speciation. The rejection of BSC demands evidence of continual gene flow until the completion of speciation. Here, we carry out the sequencing and de novo high-quality assembly of the genomes of two closely related mangrove species (Rhizophora mucronata and R. stylosa). Whole-genome re-sequencing of individuals from their distributions on the tropical coasts shows their genomes to be well delineated in allopatry. They became sympatric in northeastern Australia where their genomes harbor 9,963 and 3,874 introgression blocks, respectively, with each block averaging only about 3-4 Kb. These fine-grained introgressions indicate that gene flow continues even after numerous loci have evolved to become non-introgressable “genomic islets”. Many of these islets, only 1.4 Kb on average, harbor “speciation loci” which contribute to the divergence in flower development or gamete production and thus result in fitness reduction upon introgression. Our fine-grained analysis may thus be the first one to show that gene flow not only happens during speciation, but often continues until the completion of speciation. Under the weight of the extensive literature, BSC may deserve to be retired.

scholarly journals Molecular Signatures of Reticulate Evolution within the Complex of European Pine Taxa

Forests ◽  
2021 ◽  
Vol 12 (4) ◽  
pp. 489
Author(s):  
Bartosz Łabiszak ◽  
Witold Wachowiak
Keyword(s):  
Gene Flow ◽  
Reticulate Evolution ◽  
Modeling Framework ◽  
Closely Related Species ◽  
Interspecific Gene Flow ◽  
Nucleotide Sequence Variation ◽  
History Of ◽  
Best Fitting ◽  
Species Integrity

Speciation mechanisms, including the role of interspecific gene flow and introgression in the emergence of new species, are the major focus of evolutionary studies. Inference of taxonomic relationship between closely related species may be challenged by past hybridization events, but at the same time, it may provide new knowledge about mechanisms responsible for the maintenance of species integrity despite interspecific gene flow. Here, using nucleotide sequence variation and utilizing a coalescent modeling framework, we tested the role of hybridization and introgression in the evolutionary history of closely related pine taxa from the Pinus mugo complex and P. sylvestris. We compared the patterns of polymorphism and divergence between taxa and found a great overlap of neutral variation within the P. mugo complex. Our phylogeny reconstruction indicated multiple instances of reticulation events in the past, suggesting an important role of interspecific gene flow in the species divergence. The best-fitting model revealed P. mugo and P. uncinata as sister species with basal P. uliginosa and asymmetric migration between all investigated species after their divergence. The magnitude of interspecies gene flow differed greatly, and it was consistently stronger from representatives of P. mugo complex to P. sylvestris than in the opposite direction. The results indicate the prominent role of reticulation evolution in those forest trees and provide a genetic framework to study species integrity maintained by selection and local adaptation.

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