An analysis of the causes of genetic isolation in two Pacific Coast iris hybrid zones

1996 ◽  
Vol 74 (12) ◽  
pp. 2006-2013 ◽  
Author(s):  
Nelson D. Young
Keyword(s):  
Gene Flow ◽  
Hybrid Zone ◽  
Pacific Coast ◽  
Habitat Associations ◽  
Tube Length ◽  
Reciprocal Transplant ◽  
Hybrid Zones ◽  
Genetic Isolation ◽  
Habitat Association ◽  
Perianth Tube

In: two Pacific Coast Iris hybrid zones, the causes of genetic isolation appear to differ substantially. The Iris douglasiana – Iris innominata hybrid zone follows an ecotone a few kilometres inland from the ocean, implying different habitat associations for the two species, perhaps because of climate. Reciprocal transplant experiments showed that habitat association plays a major role in isolation. Each species survives best in its own habitat. Additional differences in perianth-tube length and flowering time between the two species have not developed into significant genetic isolating factors. The second hybrid zone occurs where species with different perianth-tube lengths co-occur (Iris chrysophylla – Iris tenax). Crosses between long- and short-tubed species suggest that differences in perianth-tube length can limit gene flow. Gene flow is also limited in the other direction, because the long-tubed species, I. chrysophylla, blooms earlier (though the flowering periods overlap). Coupled with the fact that these irises are all protandrous (anthers mature about 3 days before stigmas), relatively few days will be available when the long-tubed species can pollinate the short-tubed species. This combination of factors is probably a major form of genetic isolation in the I. chrysophylla – I. tenax zone. Keywords: speciation, reciprocal transplant, habitat association, phenology.

scholarly journals Estimates of selection and gene flow from measures of cline width and linkage disequilibrium in heliconius hybrid zones.

Genetics ◽  
1990 ◽  
Vol 124 (4) ◽  
pp. 921-936 ◽  
Author(s):  
J Mallet ◽  
N Barton ◽  
G Lamas ◽  
J Santisteban ◽  
M Muedas ◽  
...  
Keyword(s):  
Gene Flow ◽  
Hybrid Zone ◽  
Color Pattern ◽  
Butterfly Species ◽  
Hybrid Zones ◽  
Square Root ◽  
Color Patterns ◽  
Long Distance ◽  
Locus Selection ◽  
Cline Width

Abstract Hybrid zones can yield estimates of natural selection and gene flow. The width of a cline in gene frequency is approximately proportional to gene flow (sigma) divided by the square root of per-locus selection (square root of s). Gene flow also causes gametic correlations (linkage disequilibria) between genes that differ across hybrid zones. Correlations are stronger when the hybrid zone is narrow, and rise to a maximum roughly equal to s. Thus cline width and gametic correlations combine to give estimates of gene flow and selection. These indirect measures of sigma and s are especially useful because they can be made from collections, and require no field experiments. The method was applied to hybrid zones between color pattern races in a pair of Peruvian Heliconius butterfly species. The species are Müllerian mimics of one another, and both show the same changes in warning color pattern across their respective hybrid zones. The expectations of cline width and gametic correlation were generated using simulations of clines stabilized by strong frequency-dependent selection. In the hybrid zone in Heliconius erato, clines at three major color pattern loci were between 8.5 and 10.2 km wide, and the pairwise gametic correlations peaked at R approximately 0.35. These measures suggest that s approximately 0.23 per locus, and that sigma approximately 2.6 km. In erato, the shapes of the clines agreed with that expected on the basis of dominance. Heliconius melpomene has a nearly coincident hybrid zone. In this species, cline widths at four major color pattern loci varied between 11.7 and 13.4 km. Pairwise gametic correlations peaked near R approximately 1.00 for tightly linked genes, and at R approximately 0.40 for unlinked genes, giving s approximately 0.25 per locus and sigma approximately 3.7 km. In melpomene, cline shapes did not perfectly fit theoretical shapes based on dominance; this deviation might be explained by long-distance migration and/or strong epistasis. Compared with erato, sample sizes in melpomene are lower and the genetics of its color patterns are less well understood. In spite of these problems, selection and gene flow are clearly of the same order of magnitude in the two species. The relatively high per locus selection coefficients agree with "major gene" theories for the evolution of Müllerian mimicry, but the genetic architecture of the color patterns does not. These results show that the genetics and evolution of mimicry are still only sketchily understood.

scholarly journals A maladaptive combination of traits contributes to the maintenance of a stable hybrid zone between two divergent species of Drosophila

2017 ◽  
Author(s):  
Brandon S. Cooper ◽  
Alisa Sedghifar ◽  
W. Thurston Nash ◽  
Aaron A. Comeault ◽  
Daniel R. Matute
Keyword(s):  
Gene Flow ◽  
Hybrid Zone ◽  
Hybrid Zones ◽  
Hybrid Male ◽  
Open Habitat ◽  
Preferred Habitat ◽  
Species Overlap ◽  
Agricultural Areas ◽  
Stable Hybrid ◽  
Advanced Generation

ABSTRACTGeographical areas where two species come into contact and hybridize serve as natural laboratories for assessing mechanisms that limit gene flow between species. The ranges of about half of all closely related Drosophila species overlap, and the genomes of several pairs reveal signatures of past introgression. However, only two contemporary hybrid zones have been characterized in the genus, and both are recently diverged sister species (D. simulans-D. sechellia, Ks = 0.05; D. yakuba-D. santomea, Ks = 0.048). Here we present evidence of a new hybrid zone, and the ecological mechanisms that maintain it, between two highly divergent Drosophila species (Ks = 0.11). On the island of Bioko in west Africa, D. teissieri occupies mostly forests, D. yakuba occupies mostly open agricultural areas, and recently, we discovered that hybrids between these species occur near the interface of these habitats. Genome sequencing revealed that all field-sampled hybrids are F1 progeny of D. yakuba females and D. teissieri males. We found no evidence for either advanced-generation hybrids or F1 hybrids produced by D. teissieri females and D.yakuba males. The lack of advanced-generation hybrids on Bioko is consistent with mark-recapture and laboratory experiments that we conducted, which indicate hybrids have a maladaptive combination of traits. Like D. yakuba, hybrids behaviorally prefer open habitat that is relatively warm and dry, but like D. teissieri, hybrids have low desiccation tolerance, which we predict leaves them physiologically ill-equipped to cope with their preferred habitat. These observations are consistent with recent findings of limited introgression in the D. yakuba clade and identify an ecological mechanism for limiting gene flow between D. yakuba and D. teissieri; namely, selection against hybrids that we have documented, in combination with hybrid male sterility, contributes to the maintenance of this narrow (~30m), stable hybrid zone centered on the forest-open habitat ecotone. Our results show how a deleterious combination of parental traits can result in unfit or maladapted hybrids.

scholarly journals Mate choice enhances post-zygotic barriers to gene flow via ancestry bundling

2021 ◽  
Author(s):  
Pavitra Muralidhar ◽  
Graham Coop ◽  
Carl Veller
Keyword(s):  
Gene Flow ◽  
Mate Choice ◽  
Assortative Mating ◽  
Hybrid Zones ◽  
Genetic Introgression ◽  
Genetic Isolation ◽  
Common Features ◽  
Genome Wide ◽  
Zygotic Selection

Hybridization and subsequent genetic introgression are now known to be common features of the histories of many species, including our own. Following hybridization, post-zygotic selection tends to purge introgressed DNA genome-wide. While mate choice can prevent hybridization in the first place, it is also known to play an important role in post-zygotic selection against hybrids, and thus the purging of introgressed DNA. However, this role is usually thought of as a direct one: a mating preference for conspecifics reduces the sexual fitness of hybrids, reducing the transmission of introgressed ancestry. Here, we explore a second, indirect role of mate choice as a barrier to gene flow. Under assortative mating, parents covary in their ancestry, causing ancestry to be "bundled" in their offspring and later generations. This bundling effect increases ancestry variance in the population, enhancing the efficiency with which post-zygotic selection purges introgressed DNA. Using whole-genome simulations, we show that the bundling effect can comprise a substantial portion of mate choice's overall effect as a postzygotic barrier to gene flow, and that it is driven by ancestry covariances both between and within maternally and paternally inherited genomes. Using estimates of the strength of assortative mating in avian hybrid zones, we calculate that the bundling effect of mate choice may increase the amount of purging of introgressed DNA by 40-80%, contributing substantially to the genetic isolation of species.

scholarly journals Asymmetric Reproductive Barriers and Gene Flow Promote the Rise of a Stable Hybrid Zone in the Mediterranean High Mountain

2021 ◽  
Vol 12 ◽  
Author(s):  
Mohamed Abdelaziz ◽  
A. Jesús Muñoz-Pajares ◽  
Modesto Berbel ◽  
Ana García-Muñoz ◽  
José M. Gómez ◽  
...  
Keyword(s):  
Gene Flow ◽  
Reproductive Isolation ◽  
Sierra Nevada ◽  
Hybrid Zone ◽  
High Elevation ◽  
Secondary Contact ◽  
High Mountain ◽  
Hybrid Zones ◽  
Reproductive Barriers ◽  
Sierra Nevada Mountains

Hybrid zones have the potential to shed light on evolutionary processes driving adaptation and speciation. Secondary contact hybrid zones are particularly powerful natural systems for studying the interaction between divergent genomes to understand the mode and rate at which reproductive isolation accumulates during speciation. We have studied a total of 720 plants belonging to five populations from two Erysimum (Brassicaceae) species presenting a contact zone in the Sierra Nevada mountains (SE Spain). The plants were phenotyped in 2007 and 2017, and most of them were genotyped the first year using 10 microsatellite markers. Plants coming from natural populations were grown in a common garden to evaluate the reproductive barriers between both species by means of controlled crosses. All the plants used for the field and greenhouse study were characterized by measuring traits related to plant size and flower size. We estimated the genetic molecular variances, the genetic differentiation, and the genetic structure by means of the F-statistic and Bayesian inference. We also estimated the amount of recent gene flow between populations. We found a narrow unimodal hybrid zone where the hybrid genotypes appear to have been maintained by significant levels of a unidirectional gene flow coming from parental populations and from weak reproductive isolation between them. Hybrid plants exhibited intermediate or vigorous phenotypes depending on the analyzed trait. The phenotypic differences between the hybrid and the parental plants were highly coherent between the field and controlled cross experiments and through time. The highly coherent results obtained by combining field, experimental, and genetic data demonstrate the existence of a stable and narrow unimodal hybrid zone between Erysimum mediohispanicum and Erysimum nevadense at the high elevation of the Sierra Nevada mountains.

scholarly journals Absence of heterosis in hybrid crested newts

PeerJ ◽  
2018 ◽  
Vol 6 ◽  
pp. e5317 ◽  
Author(s):  
Jan W. Arntzen ◽  
Nazan Üzüm ◽  
Maja D. Ajduković ◽  
Ana Ivanović ◽  
Ben Wielstra
Keyword(s):  
Gene Flow ◽  
Hybrid Zone ◽  
Hybrid Sterility ◽  
Introgressive Hybridization ◽  
Growth Curves ◽  
Hybrid Zones ◽  
Population Demography ◽  
Interspecific Gene Flow ◽  
Fertile Hybrids ◽  
Intermediate Situation

Relationships between phylogenetic relatedness, hybrid zone spatial structure, the amount of interspecific gene flow and population demography were investigated, with the newt genusTriturusas a model system. In earlier work, a bimodal hybrid zone of two distantly related species combined low interspecific gene flow with hybrid sterility and heterosis was documented. Apart from that, a suite of unimodal hybrid zones in closely relatedTriturusshowed more or less extensive introgressive hybridization with no evidence for heterosis. We here report on population demography and interspecific gene flow in twoTriturusspecies (T. macedonicusandT. ivanbureschiin Serbia). These are two that are moderately related, engage in a heterogeneous uni-/bimodal hybrid zone and hence represent an intermediate situation. This study used 13 diagnostic nuclear genetic markers in a population at the species contact zone. This showed that all individuals were hybrids, with no parentals detected. Age, size and longevity and the estimated growth curves are not exceeding that of the parental species, so that we conclude the absence of heterosis inT. macedonicus–T. ivanbureschi. Observations across the genus support the hypothesis that fertile hybrids allocate resources to reproduction and infertile hybrids allocate resources to growth. SeveralTriturusspecies hybrid zones not yet studied allow the testing of this hypothesis.

Habitat Association of Klebsiella Species

1985 ◽  
Vol 6 (2) ◽  
pp. 52-58 ◽  
Author(s):  
Susan T. Bagley
Keyword(s):  
Drinking Water ◽  
Gastrointestinal Tract ◽  
Surface Waters ◽  
Industrial Effluents ◽  
Opportunistic Pathogen ◽  
Habitat Associations ◽  
Habitat Association ◽  
Klebsiella Species ◽  
Almost All ◽  
Polluted Waters

AbstractThe genus Klebsiella is seemingly ubiquitous in terms of its habitat associations. Klebsiella is a common opportunistic pathogen for humans and other animals, as well as being resident or transient flora (particularly in the gastrointestinal tract). Other habitats include sewage, drinking water, soils, surface waters, industrial effluents, and vegetation. Until recently, almost all these Klebsiella have been identified as one species, ie, K. pneumoniae. However, phenotypic and genotypic studies have shown that “K. pneumoniae” actually consists of at least four species, all with distinct characteristics and habitats. General habitat associations of Klebsiella species are as follows: K. pneumoniae—humans, animals, sewage, and polluted waters and soils; K. oxytoca—frequent association with most habitats; K. terrigena— unpolluted surface waters and soils, drinking water, and vegetation; K. planticola—sewage, polluted surface waters, soils, and vegetation; and K. ozaenae/K. rhinoscleromatis—infrequently detected (primarily with humans).

scholarly journals Simulating Pattern-Process Relationships to Validate Landscape Genetic Models

2012 ◽  
Vol 2012 ◽  
pp. 1-8 ◽  
Author(s):  
A. J. Shirk ◽  
S. A. Cushman ◽  
E. L. Landguth
Keyword(s):  
Gene Flow ◽  
Genetic Model ◽  
Strong Relationship ◽  
Genetic Isolation ◽  
Landscape Resistance ◽  
Oreamnos Americanus ◽  
Landscape Models ◽  
Genetic Pattern ◽  
Alternative Hypotheses ◽  
Landscape Genetic

Landscapes may resist gene flow and thereby give rise to a pattern of genetic isolation within a population. The mechanism by which a landscape resists gene flow can be inferred by evaluating the relationship between landscape models and an observed pattern of genetic isolation. This approach risks false inferences because researchers can never feasibly test all plausible alternative hypotheses. In this paper, rather than infer the process of gene flow from an observed genetic pattern, we simulate gene flow and determine if the simulated genetic pattern is related to the observed empirical genetic pattern. This is a form of inverse modeling and can be used to independently validate a landscape genetic model. In this study, we used this approach to validate a model of landscape resistance based on elevation, landcover, and roads that was previously related to genetic isolation among mountain goats (Oreamnos americanus) inhabiting the Cascade Range, Washington (USA). The strong relationship between the empirical and simulated patterns of genetic isolation we observed provides independent validation of the resistance model and demonstrates the utility of this approach in supporting landscape genetic inferences.

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