THE CHROMOSOMAL BASIS OF VIABILITY IN INTERSPECIFIC HYBRIDS BETWEEN DROSOPHILA ARIZONENSIS AND DROSOPHILA MOJAVENSIS

The chromosomal effects on differences in viability among progeny from interspecific crosses was studied in the interfertile pair Drosophila arizonensis and Drosophila mojavensis. Interspecific crossing-over was avoided by crossing hybrid males to pure-species females, and chromosomal identification in backcross progeny was possible by means of electrophoretic markers. The main findings are as follows. One chromosome supresses viability when in the heterospecific state, this being mainly so when the rest of the genotype is predominantly of mojavensis type; the other chromosomes show occasional interspecific heterosis, but are neutral in the majority of cases; interactions are not significant, except in one pair of chromosomes within a mojavensis background; there is no correlation between numbers of heterospecific chromosomes and viability scores. It is concluded that hybrid and backcross progeny inviability is not a very potent mechanism for keeping these species apart. Should etiological and ecological barriers break down, introgressive hybridization is a real possibility. The findings are compared with those from studies concerning hybrid sterility and mating behavior in these two species. It is concluded that there is no common chromosomal basis for these phenomena. In particular, the role of interspecific inversions to speciation remains obscure.

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The taxonomy and genetics of Picea rubens and its relationship to Picea mariana

Canadian Journal of Botany ◽

10.1139/b76-084 ◽

1976 ◽

Vol 54 (9) ◽

pp. 781-813 ◽

Cited By ~ 51

Author(s):

Alan G. Gordon

Keyword(s):

Picea Mariana ◽

Introgressive Hybridization ◽

Picea Rubens ◽

Interspecific Crosses ◽

Parent Species ◽

Hybrid Swarm ◽

Discrete Variation ◽

Representative Sampling ◽

Homeostatic Process ◽

Ecological Barriers

A range-wide sampling of Picea rubens Sarg. populations with a representative sampling of Picea mariana (Mill.) B.S.P. was made to investigate the variation within P. rubens and the nature and extent of hybridization between the two species. Factor analysis using 14, 21, and 24 characters, successively, indicated that the clusters of the parent species were quite discrete. Variation was found to be continuous within but not between the species, and gene flow was not more in one direction than the other. Species were found to maintain their centroides with a very low level of hybridization, and introgressive hybridization was found to be of a very limited nature.Controlled crosses indicated that the crossability of the parent species with the distantly allopatric Picea omorika ranged from 36 to 71%, while the crossability of the sympatric P. rubens × P. mariana and the reciprocal was from 1 to 3%. Other interspecific crosses were considered. Variation in the P. rubens × P. mariana F1 was substantial and sufficient to explain most of the variation observed in the occasional hybrid swarm found in nature. Backcrossing data indicate that it is not more successful than parent species crosses. Regeneration data from a soil site moisture catena for both species were evaluated to estimate the number of hybrids moving into the population relative to the parent species. These were found to be very low. A homeostatic process involving an array of both genetic and ecological barriers is proposed to explain the persistence of P. rubens in the presence of P. mariana and other selection pressures. A comparison is made of the relationships between P. glauca and P. engelmannii and that of P. rubens and P. mariana. It is concluded that the latter are not a species pair in the same sense as the former.

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Extensive hybridization between two Andean warbler species with shallow divergence in mtDNA

The Auk ◽

10.1093/ornithology/ukaa065 ◽

2021 ◽

Vol 138 (1) ◽

Cited By ~ 1

Author(s):

Laura N Céspedes-Arias ◽

Andrés M Cuervo ◽

Elisa Bonaccorso ◽

Marialejandra Castro-Farias ◽

Alejandro Mendoza-Santacruz ◽

...

Keyword(s):

Genetic Structure ◽

Contact Zone ◽

Hybrid Zone ◽

Secondary Contact ◽

Tropical Andes ◽

Phenotypic Data ◽

Geographic Ranges ◽

Intermediate Phenotypes ◽

Ecological Barriers

Abstract Studying processes acting on differentiated populations upon secondary contact, such as hybridization, is important to comprehensively understand how species are formed and maintained over time. However, avian speciation studies in the tropical Andes have largely focused on the role of topographic and ecological barriers promoting divergence in allopatry, seldom examining hybridization and introgression. We describe a hybrid zone involving 2 closely related Andean warblers (Parulidae), the Golden-fronted Redstart (Myioborus ornatus), and the Spectacled Redstart (Myioborus melanocephalus). Geographic ranges of these species abut near the Colombia-Ecuador border and many specimens from the region exhibit intermediate phenotypes, but a formal description of phenotypic variation in the contact zone was heretofore lacking. We collected specimens across a transect encompassing the area where ranges abut and areas where only “pure” parental phenotypes of M. ornatus chrysops and M. melanocephalus ruficoronatus occur. We described variation in plumage traits including patterns of head and ventral coloration and tail markings based on 321 specimens. To describe genetic variation in the contact zone and over a broader phylogeographic context, we used sequences of the mitochondrial ND2 gene for 219 individuals across the transect and the entire range of both species, including all subspecies, from Venezuela to Bolivia. We documented a hybrid zone ~200 km wide based on head coloration, where intermediate plumage phenotypes are most common and “pure” forms do not overlap geographically, consistent with extensive hybridization. Across the range of the M. ornatus–M. melanocephalus complex, mitochondrial genetic structure was shallow, with genetic breaks only coinciding clearly with one topographic feature. Such a low genetic structure is striking given the high diversity in plumage phenotypes and the current taxonomy of the group. Our phenotypic data suggest that barriers to hybridization are not strong, and allow us to postulate hypotheses to be tested using forthcoming genomic data.

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Geographical variation in postzygotic isolation and its genetic basis within and between two Mimulus species

Philosophical Transactions of the Royal Society B Biological Sciences ◽

10.1098/rstb.2010.0030 ◽

2010 ◽

Vol 365 (1552) ◽

pp. 2469-2478 ◽

Cited By ~ 51

Author(s):

Noland H. Martin ◽

John H. Willis

Keyword(s):

Pollen Fertility ◽

Genetic Basis ◽

Interspecific Cross ◽

Local Scale ◽

Interspecific Crosses ◽

Postzygotic Isolation ◽

Hybrid Fitness ◽

Pure Species ◽

Geographical Scale ◽

Germination Success

The aim of this study is to investigate the evolution of intrinsic postzygotic isolation within and between populations of Mimulus guttatus and Mimulus nasutus . We made 17 intraspecific and interspecific crosses, across a wide geographical scale. We examined the seed germination success and pollen fertility of reciprocal F 1 and F 2 hybrids and their pure-species parents, and used biometrical genetic tests to distinguish among alternative models of inheritance. Hybrid seed inviability was sporadic in both interspecific and intraspecific crosses. For several crosses, Dobzhansky–Muller incompatibilities involving nuclear genes were implicated, while two interspecific crosses revealed evidence of cytonuclear interactions. Reduced hybrid pollen fertility was found to be greatly influenced by Dobzhansky–Muller incompatibilities in five out of six intraspecific crosses and nine out of 11 interspecific crosses. Cytonuclear incompatibilities reduced hybrid fitness in only one intraspecific and one interspecific cross. This study suggests that intrinsic postzygotic isolation is common in hybrids between these Mimulus species, yet the particular hybrid incompatibilities responsible for effecting this isolation differ among the populations tested. Hence, we conclude that they evolve and spread only at the local scale.

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Homoploid hybrid speciation and genome evolution via chromosome sorting

Proceedings of The Royal Society B Biological Sciences ◽

10.1098/rspb.2015.0157 ◽

2015 ◽

Vol 282 (1807) ◽

pp. 20150157 ◽

Cited By ~ 28

Author(s):

Vladimir A. Lukhtanov ◽

Nazar A. Shapoval ◽

Boris A. Anokhin ◽

Alsu F. Saifitdinova ◽

Valentina G. Kuznetsova

Keyword(s):

Reproductive Isolation ◽

Direct Consequence ◽

Convincing Evidence ◽

Interspecific Crosses ◽

Parental Origin ◽

Hybrid Speciation ◽

Species Formation ◽

Homoploid Hybrid ◽

Creative Role

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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The role of meiotic drive in hybrid male sterility

Philosophical Transactions of the Royal Society B Biological Sciences ◽

10.1098/rstb.2009.0264 ◽

2010 ◽

Vol 365 (1544) ◽

pp. 1265-1272 ◽

Cited By ~ 71

Author(s):

Shannon R. McDermott ◽

Mohamed A. F. Noor

Keyword(s):

Male Sterility ◽

Hybrid Sterility ◽

Meiotic Drive ◽

Mechanistic Explanation ◽

Hybrid Progeny ◽

Hybrid Male ◽

Hybrid Male Sterility ◽

Species Formation ◽

Allelic Segregation

Meiotic drive causes the distortion of allelic segregation away from Mendelian expected ratios, often also reducing fecundity and favouring the evolution of drive suppressors. If different species evolve distinct drive-suppressor systems, then hybrid progeny may be sterile as a result of negative interactions of these systems' components. Although the hypothesis that meiotic drive may contribute to hybrid sterility, and thus species formation, fell out of favour early in the 1990s, recent results showing an association between drive and sterility have resurrected this previously controversial idea. Here, we review the different forms of meiotic drive and their possible roles in speciation. We discuss the recent empirical evidence for a link between drive and hybrid male sterility, also suggesting a possible mechanistic explanation for this link in the context of chromatin remodelling. Finally, we revisit the population genetics of drive that allow it to contribute to speciation.

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An autosomal factor from Drosophila arizonae restores normal spermatogenesis in Drosophila mojavensis males carrying the D. arizonae Y chromosome.

Genetics ◽

10.1093/genetics/134.1.309 ◽

1993 ◽

Vol 134 (1) ◽

pp. 309-318

Author(s):

A C Pantazidis ◽

V K Galanopoulos ◽

E Zouros

Keyword(s):

Y Chromosome ◽

Hybrid Sterility ◽

Light And Electron Microscopy ◽

Genetic Material ◽

Drosophila Mojavensis ◽

Fourth Chromosome ◽

Motility Factor ◽

Drosophila Arizonae ◽

Male Hybrid ◽

Necessary And Sufficient

Abstract Males of Drosophila mojavensis whose Y chromosome is replaced by the Y chromosome of the sibling species Drosophila arizonae are sterile. It is shown that genetic material from the fourth chromosome of D. arizonae is necessary and sufficient, in single dose, to restore fertility in these males. In introgression and mapping experiments this material segregates as a single Mendelian factor (sperm motility factor, SMF). Light and electron microscopy studies of spermatogenesis in D. mojavensis males whose Y chromosome is replaced by introgression with the Y chromosome of D. arizonae (these males are symbolized as mojYa) revealed postmeiotic abnormalities all of which are restored when the SMF of D. arizonae is co-introgressed (these males are symbolized as mojYaSMFa). The number of mature sperm per bundle in mojYaSMFa is slightly less than in pure D. mojavensis and is even smaller in males whose fertility is rescued by introgression of the entire fourth chromosome of D. arizonae. These observations establish an interspecific incompatibility between the Y chromosome and an autosomal factor (or more than one tightly linked factors) that can be useful for the study of the evolution of male hybrid sterility in Drosophila and the genetic control of spermatogenesis.

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Gene flow mediates the role of sex chromosome meiotic drive during complex speciation

eLife ◽

10.7554/elife.35468 ◽

2018 ◽

Vol 7 ◽

Cited By ~ 18

Author(s):

Colin D Meiklejohn ◽

Emily L Landeen ◽

Kathleen E Gordon ◽

Thomas Rzatkiewicz ◽

Sarah B Kingan ◽

...

Keyword(s):

Gene Flow ◽

Sex Chromosomes ◽

Population Genomics ◽

Sex Chromosome ◽

Hybrid Sterility ◽

Sequence Divergence ◽

Meiotic Drive ◽

Hybrid Male ◽

Local Sequence

During speciation, sex chromosomes often accumulate interspecific genetic incompatibilities faster than the rest of the genome. The drive theory posits that sex chromosomes are susceptible to recurrent bouts of meiotic drive and suppression, causing the evolutionary build-up of divergent cryptic sex-linked drive systems and, incidentally, genetic incompatibilities. To assess the role of drive during speciation, we combine high-resolution genetic mapping of X-linked hybrid male sterility with population genomics analyses of divergence and recent gene flow between the fruitfly species, Drosophila mauritiana and D. simulans. Our findings reveal a high density of genetic incompatibilities and a corresponding dearth of gene flow on the X chromosome. Surprisingly, we find that a known drive element recently migrated between species and, rather than contributing to interspecific divergence, caused a strong reduction in local sequence divergence, undermining the evolution of hybrid sterility. Gene flow can therefore mediate the effects of selfish genetic elements during speciation.

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When acting as a reproductive barrier for sympatric speciation, hybrid sterility can only be primary

Biological Journal of the Linnean Society ◽

10.1093/biolinnean/blz135 ◽

2019 ◽

Vol 128 (4) ◽

pp. 779-788 ◽

Cited By ~ 2

Author(s):

Donald R Forsdyke

Keyword(s):

Hybrid Sterility ◽

Sympatric Speciation ◽

The Other ◽

Reproductive Barriers ◽

Evolutionary Time ◽

Hybrid Inviability ◽

Prezygotic Isolation ◽

Microscopic Scale ◽

A New Species

Abstract Animal gametes unite to form a zygote that develops into an adult with gonads that, in turn, produce gametes. Interruption of this germinal cycle by prezygotic or postzygotic reproductive barriers can result in two cycles, each with the potential to evolve into a new species. When the speciation process is complete, members of each species are fully reproductively isolated from those of the other. During speciation a primary barrier may be supported and eventually superceded by a later-appearing secondary barrier. For those holding certain cases of prezygotic isolation to be primary (e.g. elephant cannot copulate with mouse), the onus is to show that they had not been preceded over evolutionary time by periods of postzygotic hybrid inviability (genically determined) or sterility (genically or chromosomally determined). Likewise, the onus is upon those holding cases of hybrid inviability to be primary (e.g. Dobzhansky–Muller epistatic incompatibilities) to show that they had not been preceded by periods, however brief, of hybrid sterility. The latter, when acting as a sympatric barrier causing reproductive isolation, can only be primary. In many cases, hybrid sterility may result from incompatibilities between parental chromosomes that attempt to pair during meiosis in the gonad of their offspring (Winge-Crowther-Bateson incompatibilities). While such incompatibilities have long been observed on a microscopic scale, there is growing evidence for a role of dispersed finer DNA sequence differences (i.e. in base k-mers).

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Speciation by Symbiosis: the Microbiome and Behavior

mBio ◽

10.1128/mbio.01785-15 ◽

2016 ◽

Vol 7 (2) ◽

Cited By ~ 72

Author(s):

J. Dylan Shropshire ◽

Seth R. Bordenstein

Keyword(s):

Hybrid Sterility ◽

Host Behavior ◽

Origin Of Species ◽

Behavioral Isolation ◽

Microbial Symbionts ◽

Microbial Symbiosis ◽

And Behavior ◽

Fundamental Units

ABSTRACT Species are fundamental units of comparison in biology. The newly discovered importance and ubiquity of host-associated microorganisms are now stimulating work on the roles that microbes can play in animal speciation. We previously synthesized the literature and advanced concepts of speciation by symbiosis with notable attention to hybrid sterility and lethality. Here, we review recent studies and relevant data on microbes as players in host behavior and behavioral isolation, emphasizing the patterns seen in these analyses and highlighting areas worthy of additional exploration. We conclude that the role of microbial symbionts in behavior and speciation is gaining exciting traction and that the holobiont and hologenome concepts afford an evolving intellectual framework to promote research and intellectual exchange between disciplines such as behavior, microbiology, genetics, symbiosis, and speciation. Given the increasing centrality of microbiology in macroscopic life, microbial symbiosis is arguably the most neglected aspect of animal and plant speciation, and studying it should yield a better understanding of the origin of species.

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