Incomplete reproductive isolation may promote hybrid zone formation between Ligularia tongolensis and L. cymbulifera

AbstractHybrid zones occur as range boundaries for many animal taxa. One model for how hybrid zones form and are stabilized is the tension zone model. This model predicts that hybrid zones widths are determined by a a balance between random dispersal into hybrid zones and selection against hybrids, and it does not formally account for local ecological gradients. Given the model’s simplicity, it provides a useful starting point for examining variation in hybrid zone widths across animals. Here we examine whether random dispersal and a proxy for selection against hybrids (mtDNA distance) can explain variation in hybrid zone widths across 135 hybridizing taxon pairs. We show that dispersal explains >30% of hybrid zone width variation across animal diversity and that mtDNA distance explains little variation. Clade-specific analyses revealed idiosyncratic patterns. Dispersal and mtDNA distance predict hybrid zone widths especially well in reptiles, while hybrid zone width scaled positively with mtDNA distance in birds, opposite predictions. Lastly, the data suggest that lower bounds on hybrid zone widths may be set by dispersal and the extent of molecular divergence, suggesting that hybrid zones are unlikely to form in restricted geographic spaces in highly dispersive and/or recently diverged taxa. Overall, our analyses reinforce the fundamental importance of dispersal in hybrid zone formation, and more generally in the ecology of range boundaries.

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Strong yet incomplete reproductive isolation in Vermivora is not contradicted by other lines of evidence: A reply to Toews et al.

Ecology and Evolution ◽

10.1002/ece3.7763 ◽

2021 ◽

Author(s):

Cody K. Porter ◽

John L. Confer ◽

Kyle R. Aldinger ◽

Ronald A. Canterbury ◽

Jeffrey L. Larkin ◽

...

Keyword(s):

Reproductive Isolation ◽

Incomplete Reproductive Isolation ◽

Lines Of Evidence

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X-Linked Signature of Reproductive Isolation in Humans is Mirrored in a Howler Monkey Hybrid Zone

Journal of Heredity ◽

10.1093/jhered/esaa021 ◽

2020 ◽

Vol 111 (5) ◽

pp. 419-428 ◽

Cited By ~ 1

Author(s):

Marcella D Baiz ◽

Priscilla K Tucker ◽

Jacob L Mueller ◽

Liliana Cortés-Ortiz

Keyword(s):

Reproductive Isolation ◽

X Chromosome ◽

Hybrid Zone ◽

Sex Chromosome ◽

Genomic Sequence ◽

Alouatta Palliata ◽

Model Systems ◽

Howler Monkey ◽

Autosomal Snps ◽

Outlier Region

Abstract Reproductive isolation is a fundamental step in speciation. While sex chromosomes have been linked to reproductive isolation in many model systems, including hominids, genetic studies of the contribution of sex chromosome loci to speciation for natural populations are relatively sparse. Natural hybrid zones can help identify genomic regions contributing to reproductive isolation, like hybrid incompatibility loci, since these regions exhibit reduced introgression between parental species. Here, we use a primate hybrid zone (Alouatta palliata × Alouatta pigra) to test for reduced introgression of X-linked SNPs compared to autosomal SNPs. To identify X-linked sequence in A. palliata, we used a sex-biased mapping approach with whole-genome re-sequencing data. We then used genomic cline analysis with reduced-representation sequence data for parental A. palliata and A. pigra individuals and hybrids (n = 88) to identify regions with non-neutral introgression. We identified ~26 Mb of non-repetitive, putatively X-linked genomic sequence in A. palliata, most of which mapped collinearly to the marmoset and human X chromosomes. We found that X-linked SNPs had reduced introgression and an excess of ancestry from A. palliata as compared to autosomal SNPs. One outlier region with reduced introgression overlaps a previously described “desert” of archaic hominin ancestry on the human X chromosome. These results are consistent with a large role for the X chromosome in speciation across animal taxa and further, suggest shared features in the genomic basis of the evolution of reproductive isolation in primates.

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The Roles of Sexual and Viability Selection in the Evolution of Incomplete Reproductive Isolation: From Allopatry to Sympatry

The American Naturalist ◽

10.1086/693855 ◽

2017 ◽

Vol 190 (5) ◽

pp. 680-693 ◽

Cited By ~ 12

Author(s):

Olivier Cotto ◽

Maria R. Servedio

Keyword(s):

Reproductive Isolation ◽

Viability Selection ◽

Incomplete Reproductive Isolation

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Genome-Wide Regulatory Interactions in the Early Stages of Drosophila Speciation

10.36939/ir.202012151547 ◽

2020 ◽

Author(s):

◽

Alwyn Clark Go

Keyword(s):

Reproductive Isolation ◽

Expression Analysis ◽

Regulatory Elements ◽

Specific Expression ◽

Allele Specific Expression ◽

Regulatory Interactions ◽

Early Stages ◽

Genome Wide ◽

Allele Specific ◽

Incomplete Reproductive Isolation

Speciation occurs when reproductive barriers prevent the exchange of genetic information between individuals. A common form of reproductive barrier between species capable of interbreeding is hybrid sterility. Genomic incompatibilities between the divergent genomes of different species contribute to a reduction in hybrid fitness. These incompatibilities continue to accumulate after speciation, therefore, young divergent taxa with incomplete reproductive isolation are important in understating the genetics leading to speciation. Here, I use two Drosophila subspecies pairs. The first is D. willistoni consisting of D. w. willistoni and D. w. winge. The second subspecies pair is D. pseudoobscura, which is composed of D. p. pseudoobscura and D. p. bogotana. Both subspecies pairs are at the early stages of speciation and show incomplete reproductive isolation through unidirectional hybrid male sterility. In this thesis, I performed an exploratory survey of genome-wide expression analysis using RNA-sequencing on D. willistoni and determined the extent of regulatory divergence between the subspecies using allele-specific expression analysis. I found that misexpressed genes showed a degree of tissue specificity and that the sterile male hybrids had a higher proportion of misexpressed genes in the testes relative to the fertile hybrids. The analysis of regulatory divergence between this subspecies pair found a large (66-70%) proportion of genes with conserved regulatory elements. Of the genes showing evidence or regulatory divergence between subspecies, cis-regulatory divergence was more common than other types. In the D. pseudoobscura subspecies pair, I compared sequence and expression divergence and found no support for directional selection driving gene misexpression in their hybrids. Allele-specific expression analysis revealed that compensatory cis-trans mutations partly explained gene misexpression in the hybrids. The remaining hybrid misexpression occurs due to interacting gene networks or possible co-option of cis-regulatory elements by divergent transacting factors. Overall, the results of this thesis highlight the role of regulatory interactions in a hybrid genome and how these interactions could lead to hybrid breakdown by disrupting gene interaction networks.

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Hybrid zone formation and contrasting outcomes of secondary contact over transects in common toads

Molecular Ecology ◽

10.1111/mec.14273 ◽

2017 ◽

Vol 26 (20) ◽

pp. 5663-5675 ◽

Cited By ~ 19

Author(s):

Jan W. Arntzen ◽

Wouter de Vries ◽

Daniele Canestrelli ◽

Iñigo Martínez-Solano

Keyword(s):

Hybrid Zone ◽

Secondary Contact ◽

Zone Formation

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Population genomic evidence of selection on structural variants in a natural hybrid zone

10.1101/2022.01.14.476419 ◽

2022 ◽

Author(s):

Linyi Zhang ◽

Samridhi Chaturvedi ◽

Chris Nice ◽

Lauren Lucas ◽

Zachariah Gompert

Keyword(s):

Reproductive Isolation ◽

Hybrid Zone ◽

Structural Variants ◽

Hybrid Fitness ◽

Genome Wide ◽

Oxford Nanopore ◽

Jackson Hole ◽

Long Read ◽

Genomic Regions

Structural variants (SVs) can promote speciation by directly causing reproductive isolation or by suppressing recombination across large genomic regions. Whereas examples of each mechanism have been documented, systematic tests of the role of SVs in speciation are lacking. Here, we take advantage of long-read (Oxford nanopore) whole-genome sequencing and a hybrid zone between two Lycaeides butterfly taxa (L. melissa and Jackson Hole Lycaeides) to comprehensively evaluate genome-wide patterns of introgression for SVs and relate these patterns to hypotheses about speciation. We found >100,000 SVs segregating within or between the two hybridizing species. SVs and SNPs exhibited similar levels of genetic differentiation between species, with the exception of inversions, which were more differentiated. We detected credible variation in patterns of introgression among SV loci in the hybrid zone, with 562 of 1419 ancestry-informative SVs exhibiting genomic clines that deviating from null expectations based on genome-average ancestry. Overall, hybrids exhibited a directional shift towards Jackson Hole Lycaeides ancestry at SV loci, consistent with the hypothesis that these loci experienced more selection on average then SNP loci. Surprisingly, we found that deletions, rather than inversions, showed the highest skew towards excess introgression from Jackson Hole Lycaeides. Excess Jackson Hole Lycaeides ancestry in hybrids was also especially pronounced for Z-linked SVs and inversions containing many genes. In conclusion, our results show that SVs are ubiquitous and suggest that SVs in general, but especially deletions, might contribute disproportionately to hybrid fitness and thus (partial) reproductive isolation.

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