scholarly journals Genetic structure of hybrid zones betweenPinus pumilaandP. parvifloravar.pentaphylla(Pinaceae) revealed by molecular hybrid index analysis

2004 ◽  
Vol 91 (1) ◽  
pp. 65-72 ◽  
Author(s):  
Yasuyuki Watano ◽  
Akiko Kanai ◽  
Naoki Tani
Keyword(s):  
Genetic Structure ◽  
Hybrid Zones ◽  
Hybrid Index ◽  
Index Analysis

scholarly journals Morphologically cryptic Amazonian bird species pairs exhibit strong postzygotic reproductive isolation

2018 ◽  
Vol 285 (1874) ◽  
pp. 20172081 ◽  
Author(s):  
Paola Pulido-Santacruz ◽  
Alexandre Aleixo ◽  
Jason T. Weir
Keyword(s):  
Reproductive Isolation ◽  
Amazon Basin ◽  
Species Recognition ◽  
Bird Species ◽  
Hybrid Zones ◽  
Hybrid Index ◽  
Postzygotic Isolation ◽  
Genome Wide ◽  
Species Pairs ◽  
Hybrid Classes

We possess limited understanding of how speciation unfolds in the most species-rich region of the planet—the Amazon basin. Hybrid zones provide valuable information on the evolution of reproductive isolation, but few studies of Amazonian vertebrate hybrid zones have rigorously examined the genome-wide underpinnings of reproductive isolation. We used genome-wide genetic datasets to show that two deeply diverged, but morphologically cryptic sister species of forest understorey birds show little evidence for prezygotic reproductive isolation, but substantial postzygotic isolation. Patterns of heterozygosity and hybrid index revealed that hybrid classes with heavily recombined genomes are rare and closely match simulations with high levels of selection against hybrids. Genomic and geographical clines exhibit a remarkable similarity across loci in cline centres, and have exceptionally narrow cline widths, suggesting that postzygotic isolation is driven by genetic incompatibilities at many loci, rather than a few loci of strong effect. We propose Amazonian understorey forest birds speciate slowly via gradual accumulation of postzygotic genetic incompatibilities, with prezygotic barriers playing a less important role. Our results suggest old, cryptic Amazonian taxa classified as subspecies could have substantial postzygotic isolation deserving species recognition and that species richness is likely to be substantially underestimated in Amazonia.

A Phenotypic Test of Haldane's Rule in an Avian Hybrid Zone

The Auk ◽  
2000 ◽  
Vol 117 (3) ◽  
pp. 578-585 ◽  
Author(s):  
Catherine E. Smith ◽  
Sievert Rohwer
Keyword(s):  
Pacific Northwest ◽  
Hybrid Zones ◽  
Hybrid Index ◽  
Haldane’S Rule ◽  
Haldane's Rule ◽  
The Pacific ◽  
Close Relationship ◽  
Males And Females ◽  
Heterogametic Sex ◽  
Reference Samples

Abstract We introduce a phenotypic method to test for excess mortality in hybrids of the heterogametic sex, as expected from Haldane's rule, and apply this method to the unusually narrow hybrid zones between Hermit Warblers (Dendroica occidentalis) and Townsend's Warblers (D. townsendi) in the Pacific Northwest. Our test requires establishing comparable hybrid indices for male and female warblers. The hybrid index that we developed for females produced age-corrected distributions for phenotypically pure reference samples that closely matched those used by Rohwer and Wood (1998) for males. The similarity in these distributions enabled us to compare the relative frequency of males and females in hybrids and parentals. We detected no deficiency of hybrid females and thus no inviability in the heterogametic sex. Our failure to find evidence of the inviability component of Haldane's rule is not unexpected given the close relationship between these taxa; nonetheless, our methods should be generally useful for studies of hybrid zones.

On the relation between Picea pungens and Picea engelmannii in the Rocky Mountains

1972 ◽  
Vol 50 (4) ◽  
pp. 733-742 ◽  
Author(s):  
R. Daubenmire
Keyword(s):  
Rocky Mountains ◽  
Picea Engelmannii ◽  
Hybrid Index ◽  
Geologic History ◽  
Picea Pungens ◽  
Index Analysis ◽  
History Of

Although none of the morphologic characters separating Picea pungens from P. engelmannii is absolute, a hybrid index analysis of 21 populations strongly supports a conclusion that the two species do not hybridize when they occur together in the same habitats. The characters most useful in separating the species are listed, and the geologic history of P. pungens is speculated upon.

Neutral and adaptive genomic variation in hybrid zones of two ecologically diverged Petunia species (Solanaceae)

2020 ◽  
Author(s):  
Lina Caballero-Villalobos ◽  
Gustavo A Silva-Arias ◽  
Caroline Turchetto ◽  
Giovanna C Giudicelli ◽  
Earl Petzold ◽  
...  
Keyword(s):  
Natural Selection ◽  
Genetic Structure ◽  
Reproductive Isolation ◽  
Genomic Variation ◽  
Secondary Contact ◽  
Pollination Syndrome ◽  
Hybrid Zones ◽  
Environmental Selection ◽  
Species Integrity ◽  
Well Differentiated

Abstract Hybridization between closely related plant species is a widespread phenomenon with significant evolutionary consequences, so natural hybrid zones provide exciting opportunities to study the processes of genetic differentiation and species formation. In Petunia, genetics, ecology and evolution of pollination syndromes have been thoroughly studied and related to the development of prezygotic isolation barriers between species. However, to date, no studies have explored the importance of extrinsic post-zygotic barriers such as environmental selection as drivers of reproductive isolation. In this study, we applied a population genetics approach to understand the speciation of two partially sympatric taxa of Petunia Juss that hybridize in the wild despite having strong differences in pollination syndrome, mating system and environmental requirements. We evaluated 58 individuals from seven allopatric and two contact zones of Petunia axillaris and P. exserta with genomic data to study the population genetic structure and gene exchange between these species and scan for potential loci under natural selection related to the preservation of species barriers. We explicitly evaluated the time, intensity and direction of interspecific migration, testing for alternative demographic scenarios. The genetic structure showed well-differentiated species-level lineages, and poor differentiation among populations of P. axillaris; P. exserta populations were highly structured, with several well-differentiated intraspecific lineages. Our data provide evidence for admixture with low asymmetric gene flow from P. axillaris to P. exserta associated with recent secondary contact, suggesting that pollinator specificity is not the only trait responsible for species integrity in this system. Combining the results from FST outlier and genotype–phenotype association methods, we identified 54 non-synonymous candidate variants under natural selection. Those variants are found in 35 coding sequences from which we found genes related to light-response networks, supporting that extrinsic factors such as habitat preferences can also provide a mechanism of reproductive isolation between Petunia spp. We argue that a set of pre- and post-zygotic barriers in conjunction with demographic processes maintain the species integrity.

Variation and Natural Hybridization in the Conostylis aculeata R.Br. Species Group Near Dawesville, Western Australia

1977 ◽  
Vol 25 (4) ◽  
pp. 395 ◽  
Author(s):  
SD Hopper
Keyword(s):  
Coastal Plain ◽  
Habitat Preferences ◽  
Ecological Factors ◽  
Species Group ◽  
Natural Hybridization ◽  
Hybrid Origin ◽  
Hybrid Index ◽  
Sympatric Populations ◽  
Index Analysis ◽  
Swan River

Variation was studied in allopatric and sympatric populations of Conostylis aculeata R.Br., C. candicans Endl., and C. pauciflora Hopper near Dawesville, on the Swan River Coastal Plain. When in allopatry the three species were found to be morphologically similar but distinguishable by hybrid index analysis. They also showed variable but overlapping habitat preferences. C. paucifora was morphologically intermediate between C. aculeata and a coastal ecotype of C. candicans. Sympatric populations of two pairs of species, C. candicans-C. aculeata and C. pauciflora-C. aculeata, contained intermediate hybrids with slightly reduced pollen fertility relative to the parents. Hybrid populations were confined to ruderal habitats. Ecological factors appeared to be primary in maintaining isolation between the species, since indiscriminate pollination occurred in sympatric populations, and hybrids were abundant and fertile. The taxonomic and evolutionary implications of natural hybridization in the C. aculeata group, including the possibility of a hybrid origin of C. pauciflora, are discussed.

scholarly journals Population Genetics of Heterosis: Effects of Hardy-Weinberg Disequilibrium

2004 ◽  
Vol 53 (1-6) ◽  
pp. 1-6 ◽  
Author(s):  
Rongling Wu ◽  
Ch.-X. Ma ◽  
J. Wu ◽  
W. Fang ◽  
G. Casella
Keyword(s):  
Population Genetics ◽  
Genetic Structure ◽  
Mechanistic Explanation ◽  
Hybrid Zones ◽  
Gene Effects ◽  
Weinberg Equilibrium ◽  
Hardy Weinberg Equilibrium ◽  
Two Populations ◽  
Selection Of

SummaryThe mechanistic explanation of heterosis has been traditionally based on quantitative differences of gene effects. However, for outcrossing populations, heterosis is also a property of populations. In this paper, the effects of the deviation of a population from Hardy-Weinberg equilibrium (HWE) on the magnitude of heterosis have been examined numerically. The mating of two populations in HWE may generate directions and magnitudes of heterosis different from the mating of two populations in Hardy-Weinberg disequilibrium (HWD). Such differences of heterosis between these two types of population mating may be due to the release of vigor restored in the parental populations during the process of HWD. Results from this study can provide guidance on the selection of parental populations for the effective exploitation of heterosis and the prediction of genetic structure and organization for hybrid zones in nature.

Hybridization Between the Western and Northern Call Races of the Limnodynastes-Tasmaniensis Complex (Anura, Myobatrachidae) on the Murray River in South Australia

1993 ◽  
Vol 41 (2) ◽  
pp. 101 ◽  
Author(s):  
JD Roberts
Keyword(s):  
Repetition Rate ◽  
South Australia ◽  
Dominant Frequency ◽  
Hybrid Zones ◽  
Hybrid Index ◽  
Hybrid Inviability ◽  
Call Structure ◽  
Murray River ◽  
Egg Number ◽  
Marne River

The Limnodynastes tasmaniensis complex consists of three call races: northern, southern and western. This paper documents differences in call structure between the western and northern races: differences in note repetition rate, dominant frequency, average number of notes per call and pulses per second note, but not in pulse repetition rate. The races also differ in egg size (smaller in northern) and egg number (higher in northern). There are zones of overlap between these two races west from Morgan and along the Marne River in South Australia. Mixed populations contain both parental and hybrid phenotypes. Hybrids were identified by a hybrid index based on the three call components that overlapped least (note repetition rate, dominant frequency and average number of notes per call). Temporary range expansions, associated with flooding on the Murray River, are documented for the northern call race. Artificial hybridisations revealed no evidence of hybrid inviability and this was supported by estimates of egg viability in field-collected egg masses from the Morgan zone of overlap. The hybrid zones are interpreted as zones of overlap with hybridisation where introgression is likely to occur. Biogeographic data suggest that the northern call race may be spreading south and west, displacing the western call race.

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