Homoploid hybrid speciation and genome evolution via chromosome sorting

Genomes of numerous diploid plant and animal species possess traces of interspecific crosses, and many researches consider them as support for homoploid hybrid speciation (HHS), a process by which a new reproductively isolated species arises through hybridization and combination of parts of the parental genomes, but without an increase in ploidy. However, convincing evidence for a creative role of hybridization in the origin of reproductive isolation between hybrid and parental forms is extremely limited. Here, through studying Agrodiaetus butterflies, we provide proof of a previously unknown mode of HHS based on the formation of post-zygotic reproductive isolation via hybridization of chromosomally divergent parental species and subsequent fixation of a novel combination of chromosome fusions/fissions in hybrid descendants. We show that meiotic segregation, operating in the hybrid lineage, resulted in the formation of a new diploid genome, drastically rearranged in terms of chromosome number. We also demonstrate that during the heterozygous stage of the hybrid species formation, recombination was limited between rearranged chromosomes of different parental origin, representing evidence that the reproductive isolation was a direct consequence of hybridization.

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Genetic divergence and the number of hybridizing species affect the path to homoploid hybrid speciation

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1809685115 ◽

2018 ◽

Vol 115 (39) ◽

pp. 9761-9766 ◽

Cited By ~ 13

Author(s):

Aaron A. Comeault ◽

Daniel R. Matute

Keyword(s):

Genetic Diversity ◽

Reproductive Isolation ◽

Genetic Divergence ◽

Adaptive Systems ◽

Parental Species ◽

Hybrid Speciation ◽

Hybrid Species ◽

Empirical Question ◽

Homoploid Hybrid

Hybridization is often maladaptive and in some instances has led to the loss of biodiversity. However, hybridization can also promote speciation, such as during homoploid hybrid speciation, thereby generating biodiversity. Despite examples of homoploid hybrid species, the importance of hybridization as a speciation mechanism is still widely debated, and we lack a general understanding of the conditions most likely to generate homoploid hybrid species. Here we show that the level of genetic divergence between hybridizing species has a large effect on the probability that their hybrids evolve reproductive isolation. We find that populations of hybrids formed by parental species with intermediate levels of divergence were more likely to mate assortatively, and discriminate against their parental species, than those generated from weakly or strongly diverged parental species. Reproductive isolation was also found between hybrid populations, suggesting differential sorting of parental traits across populations. Finally, hybrid populations derived from three species were more likely to evolve reproductive isolation than those derived from two species, supporting arguments that hybridization-supplied genetic diversity can lead to the evolution of novel “adaptive systems” and promote speciation. Our results illustrate when we expect hybridization and admixture to promote hybrid speciation. Whether homoploid hybrid speciation is a common speciation mechanism in general remains an outstanding empirical question.

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Hybridization and genome evolution I: The role of contingency during hybrid speciation

Current Zoology ◽

10.1093/czoolo/59.5.667 ◽

2013 ◽

Vol 59 (5) ◽

pp. 667-674 ◽

Cited By ~ 5

Author(s):

Fabrice Eroukhmanoff ◽

Richard I. Bailey ◽

Glenn-Peter Sætre

Keyword(s):

Chromosome Number ◽

Genome Evolution ◽

Hybrid Speciation ◽

Parent Species ◽

Large Role ◽

Hybrid Species ◽

Intragenomic Conflict ◽

Hybrid Swarms ◽

Homoploid Hybrid

Abstract Homoploid hybrid speciation (HHS) involves the recombination of two differentiated genomes into a novel, functional one without a change in chromosome number. Theoretically, there are numerous ways for two parental genomes to recombine. Hence, chance may play a large role in the formation of a hybrid species. If these genome combinations can evolve rapidly following hybridization and sympatric situations are numerous, recurrent homoploid hybrid speciation is a possibility. We argue that three different, but not mutually exclusive, types of contingencies could influence this process. First, many of these “hopeful monsters” of recombinant parent genotypes would likely have low fitness. Only specific combinations of parental genomic contributions may produce viable, intra-fertile hybrid species able to accommodate potential constraints arising from intragenomic conflict. Second, ecological conditions (competition, geography of the contact zones or the initial frequency of both parent species) might favor different outcomes ranging from sympatric coexistence to the formation of hybrid swarms and ultimately hybrid speciation. Finally, history may also play an important role in promoting or constraining recurrent HHS if multiple hybridization events occur sequentially and parental divergence or isolation differs along this continuum. We discuss under which conditions HHS may occur multiple times in parallel and to what extent recombination and selection may fuse the parent genomes in the same or different ways. We conclude by examining different approaches that might help to solve this intriguing evolutionary puzzle.

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Loss of sexual isolation in a hybridizing stickleback species pair

Current Zoology ◽

10.1093/czoolo/59.5.591 ◽

2013 ◽

Vol 59 (5) ◽

pp. 591-603 ◽

Cited By ~ 11

Author(s):

Alycia C. R. Lackey ◽

Janette Wenrick Boughman

Keyword(s):

Reproductive Isolation ◽

Sexual Isolation ◽

Distinct Species ◽

Mate Preferences ◽

Reproductive Barriers ◽

Species Pair ◽

Hybrid Swarm ◽

Species Formation ◽

Species Pairs

Abstract One approach to understand the importance of reproductive barriers to the speciation process is to study the breakdown of barriers between formerly distinct species. One reproductive barrier, sexual isolation, reduces gene flow between species through differences in mate preferences and mating signals and is likely important for species formation and maintenance. We measure sexual isolation in two limnetic-benthic threespine stickleback species pairs (Gasterosteus spp.). One species pair maintains strong reproductive isolation while the other species pair has recently collapsed into a hybrid swarm. We compare the strength of sexual isolation in the hybridizing pair to the currently isolated pair. We provide the first evidence that sexual isolation has been lost in the hybridizing pair and show furthermore that preferences females have for conspecific mates and the traits they use to distinguish conspecific and heterospecific males contribute to this loss. This work highlights the fragility of reproductive isolation between young species pairs and considers the role of sexual isolation in speciation.

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Rapid hybrid speciation in Darwin’s finches

Science ◽

10.1126/science.aao4593 ◽

2017 ◽

Vol 359 (6372) ◽

pp. 224-228 ◽

Cited By ~ 156

Author(s):

Sangeet Lamichhaney ◽

Fan Han ◽

Matthew T. Webster ◽

Leif Andersson ◽

B. Rosemary Grant ◽

...

Keyword(s):

Reproductive Isolation ◽

Genome Sequencing ◽

Transgressive Segregation ◽

Genetic Lineage ◽

Hybrid Speciation ◽

Galapagos Archipelago ◽

Bill Morphology ◽

Critical Scrutiny ◽

Homoploid Hybrid ◽

Geospiza Fortis

Homoploid hybrid speciation in animals has been inferred frequently from patterns of variation, but few examples have withstood critical scrutiny. Here we report a directly documented example, from its origin to reproductive isolation. An immigrant Darwin’s finch to Daphne Major in the Galápagos archipelago initiated a new genetic lineage by breeding with a resident finch (Geospiza fortis). Genome sequencing of the immigrant identified it as aG. conirostrismale that originated on Española >100 kilometers from Daphne Major. From the second generation onward, the lineage bred endogamously and, despite intense inbreeding, was ecologically successful and showed transgressive segregation of bill morphology. This example shows that reproductive isolation, which typically develops over hundreds of generations, can be established in only three.

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In search of the Goldilocks zone for hybrid speciation

10.1101/266254 ◽

2018 ◽

Author(s):

Alexandre Blanckaert ◽

Claudia Bank

Keyword(s):

New Species ◽

Reproductive Isolation ◽

Hybrid Population ◽

Hybrid Zones ◽

Hybrid Speciation ◽

Recombination Rates ◽

Relative Contribution ◽

Hybridization Event ◽

Controversial Topic ◽

Homoploid Hybrid

AbstractHybridization has recently gained considerable interest both as a unique window for observing speciation mechanisms and as a potential engine of speciation. The latter remains a controversial topic. It was recently hypothesized that the reciprocal sorting of genetic incompatibilities from parental species could result in hybrid speciation, when the hybrid population maintains a mixed combination of the parental incompatibilities that prevents further gene exchange with both parental populations. However, the specifics of the purging/sorting process of multiple incompatibilities have not been examined theoretically.We here investigate the allele-frequency dynamics of an isolated hybrid population that results from a single hybridization event. Using models of 2 or 4 loci, we investigate the fate of one or two genetic incompatibilities of the Dobzhansky-Muller type (DMIs). We study how various parameters affect both the sorting/purging of the DMIs and the probability of observing hybrid speciation by reciprocal sorting. We find that the probability of hybrid speciation is strongly dependent on the linkage architecture (i.e. the order and recombination distance between loci along chromosomes), the population size of the hybrid population, and the initial relative contribution of the parental populations to the hybrid population. We identify a Goldilocks zone for specific linkage architectures and intermediate recombination rates, in which hybrid speciation becomes highly probable. Whereas an equal contribution of parental populations to the hybrid populations maximizes the hybrid speciation probability in the Goldilocks zone, other linkage architectures yield unintuitive asymmetric maxima. We provide an explanation for this pattern, and discuss our results both with respect to the best conditions for observing hybrid speciation in nature and their implications regarding patterns of introgression in hybrid zones.SummaryHybridization is observed ubiquitously in nature. Its outcome can range from extinction to the creation of new species. With respect to the latter, the probability of homoploid hybrid speciation, i.e. the formation of a new species as a result of an hybridization event without changes in the ploidy of the organism, is a hotly debated topic. Here, we analyze a minimal model for homoploid hybrid speciation, in which reproductive isolation is achieved by means of (postzygotic) Dobzhansky-Muller incompatibilities. When these postzygotic genetic incompatibilities are resolved in the hybrid population, their reciprocal sorting can result in reproductive isolation from both parental populations, thus creating a hybrid species. We show that, in accordance with the current literature, hybrid speciation tends to be rare. However, specific arrangements of the genes responsible for reproductive isolation can make reciprocal sorting almost unavoidable and thus create barriers to the parental population in an almost deterministic matter. We discuss the implications of these results for hybrid speciation and patterns of introgression in nature.

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The role of parental and hybrid species in multiple introgression events: evidence of homoploid hybrid speciation inCentaurea(Cardueae, Asteraceae)

Botanical Journal of the Linnean Society ◽

10.1111/boj.12177 ◽

2014 ◽

Vol 175 (3) ◽

pp. 453-467 ◽

Cited By ~ 11

Author(s):

Giulia Mameli ◽

Javier López-Alvarado ◽

Emmanuele Farris ◽

Alfonso Susanna ◽

Rossella Filigheddu ◽

...

Keyword(s):

Hybrid Speciation ◽

Hybrid Species ◽

Homoploid Hybrid

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Genetic analysis of hybrid incompatibility suggests transposable elements increase reproductive isolation in the D. virilis clade

10.1101/753814 ◽

2019 ◽

Author(s):

Dean M. Castillo ◽

Leonie C. Moyle

Keyword(s):

Transposable Elements ◽

Reproductive Isolation ◽

Interspecific Cross ◽

Drosophila Virilis ◽

Interspecific Crosses ◽

Closely Related Species ◽

Hybrid Incompatibility ◽

Alternative Hypotheses ◽

Hybrid Dysfunction

AbstractAlthough observed in many interspecific crosses, the genetic basis of most hybrid incompatibilities is still unknown. Mismatches between parental genomes in selfish elements and the genes that regulate these elements are frequently hypothesized to underlie hybrid dysfunction. We evaluated the potential role of transposable elements (TEs) in hybrid incompatibilities by examining hybrids between Drosophila virilis strains polymorphic for TEs that cause dysgenesis and a closely related species that appears to lack these elements. Using genomic data, we confirmed copy number differences in potentially causal TEs between the dysgenic-causing D. virilis (TE+) strain and a sensitive D. virilis (TE-) strain and D. lummei genotype. We then contrasted isolation phenotypes in a cross where dysgenic TEs are absent from both D. virilis (TE-) and D. lummei parental genotypes, to a cross where dysgenic TEs are present in the D. virilis (TE+) parent and absent in the D. lummei parent, predicting increased reproductive isolation in the latter cross. Using F1 and backcross experiments that account for alternative hypotheses, we demonstrated amplified reproductive isolation specifically in the interspecific cross involving TE+ D. virilis, consistent with the action of dysgenesis-inducing TEs. These experiments demonstrate that TEs can contribute to hybrid incompatibilities via presence/absence polymorphisms.

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170 Years of “Lock-and-Key”: Genital Morphology and Reproductive Isolation

International Journal of Evolutionary Biology ◽

10.1155/2012/247352 ◽

2012 ◽

Vol 2012 ◽

pp. 1-10 ◽

Cited By ~ 75

Author(s):

John P. Masly

Keyword(s):

Reproductive Isolation ◽

Animal Species ◽

Species Differences ◽

Convincing Evidence ◽

Genital Morphology ◽

Intuitive Appeal ◽

History Of ◽

Structural Isolation ◽

Future Work

The divergent genital morphology observed among closely related animal species has long been posited as a mechanism of reproductive isolation. Despite the intuitive appeal that rapidly evolving genitalia might cause speciation, evidence for its importance—or even its potential—in reproductive isolation is mixed. Most tests of genital structural isolation between species often fail to find convincing evidence that differences in morphology prevent copulation or insemination between species. However, recent work suggests that differences in genital morphology might contribute to reproductive isolation in less obvious ways through interactions with sensory mechanisms that result in lowered reproductive fitness in heterospecific matings. In this paper, I present a brief history of the “lock-and-key” hypothesis, summarize the evidence for the involvement of genital morphology in different mechanisms of reproductive isolation, discuss progress in identifying the molecular and genetic bases of species differences in genital morphology, and discuss prospects for future work on the role of genitalia in speciation.

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A triple combination of treatments on moderate COVID-19

Open Medicine ◽

10.1515/med-2021-0279 ◽

2021 ◽

Vol 16 (1) ◽

pp. 769-772

Author(s):

ChunMiao Bao ◽

BinBin Li ◽

YuFeng Zhou

Keyword(s):

Medical Records ◽

Clinical Characteristics ◽

Smoking Status ◽

Length Of Hospital Stay ◽

Convincing Evidence ◽

Triple Combination ◽

Viral Shedding ◽

Null Effect ◽

Treatment Start

Abstract Objective A triple combination of interferon (IFN) α-2b, lopinavir tablets, and umifenovir was used to treat COVID-19 patients. It is important to explore whether the benefit of this therapy is time dependent. Methods A cohort of moderate COVID-19 patients (n = 54) was admitted for hospitalization. The demographic (age, gender, and smoking status) and clinical characteristics (epidemiological trace and comorbidity) were collected from the digital medical records. The length of hospital stay (LOS) and the viral shedding time (VST) were set as the outcomes for COVID-19 cases. Results After control for age, sex, epidemiological trace, smoking, and comorbidity, the time of treatment start had null effect on VST (IRR = 1.09; 95% CI = 0.91–1.30; p = 0.33) or LOS (IRR = 1.10; 95% CI = 0.94–1.28; p = 0.23). Conclusion There is no convincing evidence to support a pivotal role of the timing of the therapy in the prognosis of moderate COVID-19 cases.

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Speciation and changes in male gene expression in Drosophila

Genome ◽

10.1139/gen-2020-0025 ◽

2020 ◽

pp. 1-11

Author(s):

Bahar Patlar ◽

Alberto Civetta

Keyword(s):

Gene Expression ◽

Reproductive Isolation ◽

Potential Role ◽

Regulation Of Gene Expression ◽

Drosophila Model ◽

Depth Analysis ◽

The Impact ◽

Plastic Responses ◽

Male Gene

It has long been acknowledged that changes in the regulation of gene expression may account for major organismal differences. However, we still do not fully understand how changes in gene expression evolve and how do such changes influence organisms’ differences. We are even less aware of the impact such changes might have in restricting gene flow between species. Here, we focus on studies of gene expression and speciation in the Drosophila model. We review studies that have identified gene interactions in post-mating reproductive isolation and speciation, particularly those that modulate male gene expression. We also address studies that have experimentally manipulated changes in gene expression to test their effect in post-mating reproductive isolation. We highlight the need for a more in-depth analysis of the role of selection causing disrupted gene expression of such candidate genes in sterile/inviable hybrids. Moreover, we discuss the relevance to incorporate more routinely assays that simultaneously evaluate the potential effects of environmental factors and genetic background in modulating plastic responses in male genes and their potential role in speciation.

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