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98 results for “hybrid speciation”
Data from: Chromosome-scale inference of hybrid speciation and admixture with convolutional neural networks
<p>Inferring the frequency and mode of hybridization among closely related organisms is an important step for understanding the process of speciation and can help to uncover reticulated patterns of phylogeny more generally. Phylogenomic methods to test for the presence of hybridization come in many varieties and typically operate by leveraging expected patterns of genealogical discordance in the absence of hybridization. An important assumption made by these tests is that the data (genes or SNPs) are independent given the species tree. However, when the data are closely linked, it is especially important to consider their non-independence. Recently, deep learning techniques such as convolutional neural networks (CNNs) have been used to perform population genetic inferences with linked SNPs coded as binary images. Here we use CNNs for selecting among candidate hybridization scenarios using the tree topology (((P<sub>1</sub>,P<sub>2</sub>),P<sub>3</sub>),Out) and a matrix of pairwise nucleotide divergence (d<sub>XY</sub>) calculated in windows across the genome. Using coalescent simulations to train and independently test a neural network showed that our method, HyDe-CNN, was able to accurately perform model selection for hybridization scenarios across a wide-breath of parameter space. We then used HyDe-CNN to test models of admixture in <em>Heliconius</em> butterflies, as well as comparing it to a random forest classifier trained on introgression-based statistics. Given the flexibility of our approach, the dropping cost of long-read sequencing, and the continued improvement of CNN architectures, we anticipate that inferences of hybridization using deep learning methods like ours will help researchers to better understand patterns of admixture in their study organisms.</p>
Data from: Independent homoploid hybrid speciation events in the Macaronesian endemic genus Argyranthemum
Well-characterised examples of homoploid hybrid speciation (HHS) are rare in nature yet they offer the potential to study a number of evolutionary processes. In this study we investigate putative homoploid hybrid species in the genus Argyranthemum (Asteraceae), a group of plants endemic to the Macaronesian archipelagos of the North Atlantic Ocean. We specifically address a number of knowledge gaps surrounding the origin(s) of A. sundingii and A. lemsii, which are thought to be derived from the same parental cross. Comparisons of leaf morphology suggest that A. sundingii and A. lemsii are distinct from their parental progenitors and distinguishable from each other based on leaf area. Ecological niche modelling (ENM) demonstrated that the homoploid hybrid species occupy novel habitats that are intermediate relative to the parental species. Nuclear SSRs and SNP data indicate that the homoploid hybrid species are distinct from the parental taxa, whilst population level sampling of chloroplast SSRs and Approximate Bayesian Computation show that A. sundingii and A. lemsii are independently derived from the same parental cross. As such, Argyranthemum represents an example of independent homoploid hybrid speciation events with evidence of divergence in leaf morphology and adaptation to novel intermediate habitats. On oceanic islands, which are often typified by steep ecological gradients and inhabited by recently derived species with weak reproductive barriers, multiple HHS events from the same parental cross are not only possible but are likely to have played a more important role in oceanic island radiations than we currently think.
Data from: Geographic variation in the structure of oak hybrid zones provides insights into the dynamics of speciation
Studying geographic variation in the rate of hybridization between closely related species could provide a useful window to understand the evolution of reproductive isolation. Reinforcement theory predicts greater prezygotic isolation in areas of prolonged contact between recently diverged species than in areas of recent contact, which implies that old contact zones would be dominated by parental phenotypes with few hybrids (bimodal hybrid zones) whereas recent contact zones would be characterized by hybrid swarms (unimodal hybrid zones). Here we investigate how the hybrid zones of two closely related Chinese oaks, Quercus mongolica and Q. liaotungensis, are structured geographically using both nuclear and chloroplast markers. We found that populations of Q. liaotungensis located around the Changbai Mountains in Northeast China, an inferred glacial refugium, are introgressed by genes from Q. mongolica, suggesting former contact between the two species in this region. Yet, these introgressed populations form sharp bimodal hybrid zones with Q. mongolica. In contrast, populations of Q. liaotungensis located in North China, which show no sign of ancient introgression with Q. mongolica, form unimodal hybrid zones with Q. mongolica. These results are consistent with the hypothesis that selection against hybrids has had sufficient time to reinforce the reproductive barriers between Q. liaotungensis and Q. mongolica in Northeast China but not in North China.
Data from: Timeframes of speciation, reticulation, and hybridization in the Bulldog bat explained through phylogenetic analyses of all genetic transmission elements
Phylogenetic comparisons of the different mammalian genetic transmission elements (mtDNA, X-, Y-, and autosomal DNA) is a powerful approach for understanding the process of speciation in nature. Through such comparisons the unique inheritance pathways of each genetic element and gender-biased processes can link genomic structure to the evolutionary process, especially among lineages which have recently diversified, in which genetic isolation may be incomplete. Bulldog bats of the genus Noctilio are an exemplar lineage, being a young clade, widely distributed, and exhibiting unique feeding ecologies. In addition, currently recognized species are paraphyletic with respect to the mtDNA gene tree and contain morphologically identifiable clades that exhibit mtDNA divergences as great as among many species. To test taxonomic hypotheses and understand the contribution of hybridization to the extant distribution of genetic diversity in Noctilio, we used phylogenetic, coalescent stochastic modeling, and divergence time estimates using sequence data from cytochrome-b, cytochrome c oxidase-I, zinc finger Y, and zinc finger X, as well as evolutionary reconstructions based on amplified fragment length polymorphisms (AFLP) data. No evidence of ongoing hybridization between the two currently recognized species was identified. However, signatures of an ancient mtDNA capture were recovered in which an mtDNA lineage of one species was captured early in the noctilionid radiation. Among subspecific mtDNA clades, which were generally coincident with morphology and statistically definable as species, signatures of ongoing hybridization were observed in sex chromosome sequences and AFLP. Divergence dating of genetic elements corroborates the diversification of extant Noctilio beginning about three million years ago, with ongoing hybridization between mitochondrial lineages separated by 2.5 million years. The time-frame of species' divergence within Noctilio supports the hypothesis that shifts in the dietary strategies of gleaning insects (N. albiventris) or fish (N. leporinus) are among the most rapid instances of dietary evolution observed in mammals. This study illustrates the complex evolutionary dynamics shaping gene pools in nature, how comparisons of genetic elements can serve for understanding species boundaries, and the complex considerations for accurate taxonomic assignment.
Data from: A Z-linked sterility locus causes sexual abstinence in hybrid females and facilitates speciation in Spodoptera frugiperda
In the fall armyworm, Spodoptera frugiperda (Lepidoptera, Noctuidae), two sympatric strains have been recognized that have been termed corn strain (C) and rice strain (R), referring to their most common host plants. Both strains are reproductively isolated via a distinct prezygotic barrier as well as via an intriguing postzygotic phenomenon: when R females have mated with C males, the resulting RC hybrid females exhibit dramatically reduced fertility independent of their mating partner. Here we demonstrate that the reduced fertility is caused by the fact that these females refrain from mating, i.e. females are behaviorally sterile. We identified a Z-chromosomally linked sterility locus that is most likely incompatible with yet-to-be-identified autosomal (or cytoplasmic) factors leading to the observed sexual abstinence. Within-chromosome mapping revealed the sterility locus to be located in an area of strongly reduced inter-strain recombination.
Data from: The last bastion? X chromosome genotyping of Anopheles gambiae species pair males from a hybrid zone reveals complex recombination within the major candidate 'genomic island of speciation'
Speciation with gene flow may be aided by reduced recombination helping to build linkage between genes involved in the early stages of reproductive isolation. Reduced recombination on chromosome X has been implicated in speciation within the Anopheles gambiae complex, species of which represent the major Afrotropical malaria vectors. The most recently diverged, morphologically indistinguishable, species pair, A. gambiae and Anopheles coluzzii, ubiquitously displays a 'genomic island of divergence' spanning over 4 Mb from chromosome X centromere, which represents a particularly promising candidate region for reproductive isolation genes, in addition to containing the diagnostic markers used to distinguish the species. Very low recombination makes the island intractable for experimental recombination studies, but an extreme hybrid zone in Guinea Bissau offers the opportunity for natural investigation of X-island recombination. SNP analysis of chromosome X hemizygous males revealed: (i) strong divergence in the X-island despite a lack of autosomal divergence; (ii) individuals with multiple-recombinant genotypes, including likely double crossovers and localized gene conversion; (iii) recombination-driven discontinuity both within and between the molecular species markers, suggesting that the utility of the diagnostics is undermined under high hybridization. The largely, but incompletely protected nature of the X centromeric genomic island is consistent with a primary candidate area for accumulation of adaptive variants driving speciation with gene flow, while permitting some selective shuffling and removal of genetic variation.
Data from: Arabidopsis hybrid speciation processes
The genus Arabidopsis provides a unique opportunity to study fundamental biological questions in plant sciences utilizing the diploid model species A. thaliana and A. lyrata. However, only a few studies have focused on introgression and hybrid speciation in Arabidopsis, although polyploidy is a common phenomenon within this genus. More recently, there is growing evidence of significant gene flow between the various Arabidopsis species. So far, we know A. suecica and A. kamchatica as fully stabilized allopolyploid species. Both species evolved during Pleistocene glaciation and deglaciation cycles in Fennoscandinavia and the amphi-Beringian region, respectively. These hybrid studies were conducted either on a phylogeographic scale, or hybridization was reconstructed experimentally in the laboratory. With our study we focus at a regional and populational level. Our research area is located in the foothills of the Eastern Austrian Alps, where two Arabidopsis species, A. arenosa and A. lyrata ssp. petraea, are sympatrically distributed. Our hypothesis of genetic introgression, migration, and adaptation to the changing environment during the Pleistocene has been confirmed: We observed significant, mainly unidirectional gene flow between the two species, which has given rise to the tetraploid A. lyrata. This cytotype was able to escape from the narrow ecological niche occupied by diploid A. lyrata ssp. petraea on limestone outcrops by migrating northward into siliceous areas, leaving behind a trail of genetic differentiation.
Data from: Structure and dynamics of hybrid zones at multiple stages of speciation in the common vole (Microtus arvalis)
The genetic structure and dynamics of hybrid zones provides crucial information for the understanding of the processes and mechanisms of evolutionary divergence and speciation. In general, higher levels of evolutionary divergence between taxa are more likely to be associated with reproductive isolation and may result in suppressed or strongly restricted hybridization. In this study, we examined the structure and processes in two secondary contact zones between three deep evolutionary lineages in the common vole (Microtus arvalis). Differences in divergence times between the lineages have the potential to shed light on different stages of reproductive isolation and thus provide information on the ongoing speciation process in M. arvalis. We examined more than 800 individuals for mitochondrial (mtDNA), Y-chromosome and autosomal markers, and used assignment and cline analysis methods to characterize the extent and direction of gene flow in the contact zones. Introgression of both autosomal and mtDNA markers in a relatively broad area of admixture indicates selectively neutral hybridization between the least-divergent lineages (Central and Eastern) without evidence for partial reproductive isolation. In contrast, a very narrow area of hybridization, shifts in marker clines and the quasi-absence of Y-chromosome introgression support a moving hybrid zone and unidirectional selection against male hybrids between the lineages with older divergence (Central and Western). Data from a replicate sampling transect provided further support for non-neutral processes in this hybrid zone and suggests additionally a role for the landscape history in the extent of the movement and shaping of gene flow profiles.
Data from: Sticky genomes: using NGS evidence to test hybrid speciation hypotheses
Hypotheses of hybrid origin are common. Here we use next generation sequencing to test a hybrid hypothesis for a non-model insect with a large genome. We compared a putative hybrid triploid stick insect species (Acanthoxyla geisovii) with its putative paternal diploid taxon (Clitarchus hookeri), a relationship that provides clear predictions for the relative genetic diversity within each genome. The parental taxon is expected to have comparatively low allelic diversity that is nested within the diversity of the hybrid daughter genome. The scale of genome sequencing required was conveniently achieved by extracting mRNA and sequencing cDNA to examine expressed allelic diversity. This allowed us to test hybrid-progenitor relationships among non-model organisms with large genomes and different ploidy levels. Examination of thousands of independent loci avoids potential problems produced by the silencing of parts of one or other of the parental genomes, a phenomenon sometimes associated with the process of stabilisation of a hybrid genome. Transcript assembles were assessed for evidence of paralogs and/or alternative splice variants before proceeding. Comparison of transcript assemblies was not an appropriate measure of genetic variability, but by mapping reads back to clusters derived from each species we determined levels of allelic diversity. We found greater cDNA sequence diversity among alleles in the putative hybrid species (Acanthoxyla geisovii) than the non-hybrid. The allelic diversity within the putative paternal species (Clitachus hookeri) nested within the hybrid-daughter genome, supports the current view of a hybrid-progenitor relationship for these stick insect species. Next generation sequencing technology provides opportunities for testing evolutionary hypotheses with non-model organisms, including, as here, genomes that are large due to polyploidy
Data from: Hybrid speciation by sorting of parental incompatibilities in Italian sparrows
Speciation by hybridization is emerging as a significant contributor to biological diversification. Yet, little is known about the relative contributions of (i) evolutionary novelty and (ii) sorting of preexisting parental incompatibilities to the build-up of reproductive isolation under this mode of speciation. Few studies have addressed empirically whether hybrid animal taxa are intrinsically isolated from their parents, and no study has so far investigated by which of the two aforementioned routes intrinsic barriers evolve. Here, we show that sorting of preexisting parental incompatibilities contributes to intrinsic isolation of a hybrid animal taxon. Using a genomic cline framework, we demonstrate that the sex-linked and mito-nuclear incompatibilities isolating the homoploid hybrid Italian sparrow at its two geographically separated hybrid-parent boundaries represent a subset of those contributing to reproductive isolation between its parent species, house and Spanish sparrows. Should such a sorting mechanism prove to be pervasive, the circumstances promoting homoploid hybrid speciation may be broader than currently thought, and indeed there may be many cryptic hybrid taxa separated from their parent species by sorted, inherited incompatibilities.
Data from: Hybridization masks speciation in the evolutionary history of the Galápagos marine iguana
The effects of the direct interaction between hybridization and speciation—two major contrasting evolutionary processes—are poorly understood. We present here the evolutionary history of the Galápagos marine iguana (Amblyrhynchus cristatus) and reveal a case of incipient within-island speciation, which is paralleled by between-island hybridization. In-depth genome-wide analyses suggest that Amblyrhynchus diverged from its sister group, the Galápagos land iguanas, around 4.5 million years ago (Ma), but divergence among extant populations is exceedingly young (less than 50 000 years). Despite Amblyrhynchus appearing as a single long-branch species phylogenetically, we find strong population structure between islands, and one case of incipient speciation of sister lineages within the same island—ostensibly initiated by volcanic events. Hybridization between both lineages is exceedingly rare, yet frequent hybridization with migrants from nearby islands is evident. The contemporary snapshot provided by highly variable markers indicates that speciation events may have occurred throughout the evolutionary history of marine iguanas, though these events are not visible in the deeper phylogenetic trees. We hypothesize that the observed interplay of speciation and hybridization might be a mechanism by which local adaptations, generated by incipient speciation, can be absorbed into a common gene pool, thereby enhancing the evolutionary potential of the species as a whole.
Data from: Hybrid speciation in sparrows I: phenotypic intermediacy, genetic admixture and barriers to gene flow
Homoploid hybrid speciation is thought to require unusual circumstances to yield reproductive isolation from the parental species, and few examples are known from nature. Here we present genetic evidence for this mode of speciation in birds. Using Bayesian assignment analyses of 751 individuals genotyped for 14 unlinked, nuclear microsatellite loci, we show that the phenotypically intermediate Italian sparrow (Passer italiae) does not form a cluster of its own, but instead exhibits clear admixture (over its entire breeding range) between its putative parental species, the house sparrow (P. domesticus) and the Spanish sparrow (P. hispaniolensis). Further, the Italian sparrow possesses mitochondrial (mt) DNA haplotypes identical to both putative parental species (although mostly of house sparrow origin), indicating a recent hybrid origin. Today, the Italian sparrow has a largely allopatric distribution on the Italian peninsula and some Mediterranean islands separated from its suggested parental species by the Alps and the Mediterranean Sea, but occurs sympatrically with the Spanish sparrow on the Gargano peninsula in southeast Italy. No evidence of interbreeding was found in this sympatric population. However, the Italian sparrow hybridizes with the house sparrow in a sparsely populated contact zone in the Alps. Yet, the contact zone is characterized by steep clines in species-specific male plumage traits, suggesting that partial reproductive isolation may also have developed between these two taxa. Thus, geographic and reproductive barriers restrict gene flow into the nascent hybrid species. We propose that an origin of hybrid species where the hybrid lineage gets geographically isolated from the parental species, as seems to have happened here, might be more common in nature than previously assumed.
Data from: Limits to speciation inferred from times to secondary sympatry and ages of hybridizing species along a latitudinal gradient
Range expansions are critical to renewed bouts of allopatric or parapatric speciation. Limits on range expansions—and, by implication, speciation—include dispersal ability and permeability of geographical barriers. In addition, recently diverged taxa may interfere with each other, preventing mutual expansion of each other's range into sympatry, because reproductive isolation is incomplete and/or ecological competition particularly strong. On the basis of geographical distributions and mitochondrial DNA phylogenetic information for 418 recently diverged species of New World birds, we estimate that secondary sympatry takes on the order of millions of years following population splitting and hence could impose an important limit on the rate of range expansion, thereby limiting further rounds of species formation. Average rates of achievement of sympatry have been faster in the temperate region (we estimate 1.7 million years to sympatry at 60°) than in the tropics (3.2 million years to sympatry at the equator). Evidence from the ages of species with hybrid zones implies that one factor associated with the slowed sympatry in the tropics is the rate of accumulation of reproductive isolation.
Heterosis counteracts hybrid breakdown to forestall speciation by parallel natural selection
<p>In contrast to ecological speciation, where reproductive isolation evolves as a consequence of divergent natural selection, speciation by parallel natural selection has been less thoroughly studied. To test whether parallel evolution drives speciation, we leveraged the repeated evolution of benthic and limnetic ecotypes of threespine stickleback fish and estimated fitness for pure crosses and within-ecotype hybrids in semi-natural ponds and in laboratory aquaria. In ponds, we detected hybrid breakdown in both ecotypes but this was counterbalanced by heterosis and the strength of post-zygotic isolation was nil. In aquaria, we detected heterosis only in limnetic crosses and breakdown in neither ecotype, suggesting that hybrid incompatibilities are environment-dependent for both ecotypes and that heterosis is environment-dependent in benthic crosses. Heterosis and breakdown were 3× greater in limnetic crosses than in benthic crosses, contrasting the prediction that the fitness consequences of hybridization should be greater in crosses among more derived ecotypes. Consistent with a primary role for stochastic processes, patterns differed among crosses between populations from different lakes. Yet, we observed qualitatively similar patterns of heterosis and hybrid breakdown in benthic crosses and limnetic crosses when averaging the lake pairs, suggesting that the outcome of hybridization is repeatable in a general sense.</p>
Fig. 8 Haplotype network for 44 in New insights into the phylogeny and taxonomy of Chinese species of Gagea (Liliaceae)-speciation through hybridization
Fig. 8 Haplotype network for 44 cpDNA haplotypes (psbA-trnH IGS+trnL-trnF IGS) including 38 sequences of representatives of Gagea sect. Gagea: G. aipetriensis (aip), G. ancestralis, G. angelae (ang), G. artemczukii (art), G. capusii (cap), G. erubescens (eru), G. helenae (hel), G. huochengensis (huo), G. lutea (lut), G. nakaiana (nak), G. paczoskii (pac), G. podolica (pod), G. pomeranica (pom), G. pratensis (pra), G. pusilla (pus), G. rubicunda (rub), G. shmakoviana (shm), G. terraccianoana (ter), G. tisoniana (tis), G.
FIGURE 6 in Ranunculus schmalhausenii (section Batrachium, Ranunculaceae), a neglected water crowfoot endemic to Fennoscandia-a case of rapid hybrid speciation in postglacial environment of North Europe
FIGURE 6. Ranunculus schmalhausenii in the wild in Republic of Karelia, Russia: A—plant in deep water of lake Srednee Kuito (vicinity of town Kalevala), B—whole plant in the shallow of lake Bolshoe Severnoe (vicinity of village Sosnovyi), C, D—floating upper vegetativegenerative part in the shallow of lake Bolshoe Severnoe (vicinity of village Sosnovyi). Photos A.A. Bobrov, (A) 16 July 2012, (B–D) 17 July 2012.
FIGURE 5 in Ranunculus schmalhausenii (section Batrachium, Ranunculaceae), a neglected water crowfoot endemic to Fennoscandia-a case of rapid hybrid speciation in postglacial environment of North Europe
FIGURE 5. Herbarium specimens (H) of Ranunculus schmalhausenii of different morphotypes: A—typical lake form (Russia, Murmansk region, lake Notozero, H 801405), B—typical river form (Finland, Kittilä Lapland, Ylikylä, H 801383), C—form with lobed petals (Finland, Finland proper, Jalassaari, H 801409), D—form with many petaled flowers (Finland, South Häme, lake Norijärvi, H 043172).
FIGURE 4 in Ranunculus schmalhausenii (section Batrachium, Ranunculaceae), a neglected water crowfoot endemic to Fennoscandia-a case of rapid hybrid speciation in postglacial environment of North Europe
FIGURE 4. Phylogenetic relations within Batrachium taxa based on the rpl32-trnL region. Unrooted tree was built in MEGA5 using Maximum Likelihood method (ML). Bootstrap support values from 1000 replicates are shown next to the branches.
FIGURE 8 in Ranunculus schmalhausenii (section Batrachium, Ranunculaceae), a neglected water crowfoot endemic to Fennoscandia-a case of rapid hybrid speciation in postglacial environment of North Europe
FIGURE 8. Individual plant of Ranunculus schmalhausenii (Russia, Republic of Karelia, lake Verknyaya Kuzemka, IBIW) with different types of shoots: A—vegetative, prostrate shoots, B—lower part of generative shoot, C—upper part of generative shoot.
FIGURE 1 in Ranunculus schmalhausenii (section Batrachium, Ranunculaceae), a neglected water crowfoot endemic to Fennoscandia-a case of rapid hybrid speciation in postglacial environment of North Europe
FIGURE 1. Geographical range of Ranunculus schmalhausenii (outlined) with the localities of field investigation and DNA sampling in Finland and North-West of European Russia (dots). Dash line shows preliminary range border due to insufficient data.
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