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.

How often do they do it? An in-depth analysis of the hybrid zone of two grass snake species (Natrix astreptophora and Natrix helvetica)

2020 ◽  
Vol 131 (4) ◽  
pp. 756-773
Author(s):  
Marika Asztalos ◽  
Nadine Schultze ◽  
Flora Ihlow ◽  
Philippe Geniez ◽  
Matthieu Berroneau ◽  
...  
Keyword(s):  
Contact Zone ◽  
Hybrid Zone ◽  
Climatic Conditions ◽  
Secondary Contact ◽  
Distribution Models ◽  
Long Distance ◽  
Depth Analysis ◽  
Grass Snake ◽  
Genetic Signatures ◽  
Cline Width

Abstract We examined the contact zone of two parapatric species of grass snake (Natrix astreptophora and Natrix helvetica) in southern France. To this end, we used comprehensive sampling, analysed mtDNA sequences and microsatellite loci, and built Species Distribution Models for current and past climatic conditions. The contact zone had established by the mid-Holocene during range expansions from glacial refuges in the Iberian Peninsula (N. astreptophora) and southern or western France (N. helvetica). The contact zone represents a narrow bimodal hybrid zone, with steep genetic transition from one taxon to the other and rare hybridization, supporting species status for N. astreptophora and N. helvetica. Our results suggest that the steepness of the clines is a more robust tool for species delimitation than cline width. In addition, we discovered in western France, beyond the hybrid zone, a remote population of N. helvetica with genetic signatures of hybridization with N. astreptophora, most likely the result of human-mediated long-distance dispersal. For N. helvetica, we identified a southern and a northern population cluster, connected by broad-scale gene flow in a unimodal hybrid zone running across France. This pattern either reflects genetic divergence caused by allopatry in two microrefuges and subsequent secondary contact or introgression of foreign alleles into the southern cluster.

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.

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.

Functional significance of preserved color patterns of mollusks from the Gosport Sand (Eocene) of Alabama

1988 ◽  
Vol 62 (01) ◽  
pp. 83-87 ◽  
Author(s):  
Patricia H. Kelley ◽  
Charles T. Swann
Keyword(s):  
Functional Morphology ◽  
Functional Significance ◽  
Intraspecific Variability ◽  
Color Pattern ◽  
Color Patterns ◽  
Historical Factors ◽  
Life Mode ◽  
Molluscan Fauna ◽  
Excellent Preservation ◽  
Architectural Constraints

The excellent preservation of the molluscan fauna from the Gosport Sand (Eocene) at Little Stave Creek, Alabama, has made it possible to describe the preserved color patterns of 15 species. In this study the functional significance of these color patterns is tested in the context of the current adaptationist controversy. The pigment of the color pattern is thought to be a result of metabolic waste disposal. Therefore, the presence of the pigment is functional, although the patterns formed by the pigment may or may not have been adaptive. In this investigation the criteria proposed by Seilacher (1972) for testing the functionality of color patterns were applied to the Gosport fauna and the results compared with life mode as interpreted from knowledge of extant relatives and functional morphology. Using Seilacher's criteria of little ontogenetic and intraspecific variability, the color patterns appear to have been functional. However, the functional morphology studies indicate an infaunal life mode which would preclude functional color patterns. Particular color patterns are instead interpreted to be the result of historical factors, such as multiple adaptive peaks or random fixation of alleles, or of architectural constraints including possibly pleiotropy or allometry. The low variability of color patterns, which was noted within species and genera, suggests that color patterns may also serve a useful taxonomic purpose.

Long distance pollen-mediated gene flow at a landscape level: the weed beet as a case study

2007 ◽  
Vol 16 (18) ◽  
pp. 3801-3813 ◽  
Author(s):  
STÉPHANE FÉNART ◽  
FRÉDÉRIC AUSTERLITZ ◽  
JOËL CUGUEN ◽  
JEAN-FRANÇOIS ARNAUD
Keyword(s):  
Gene Flow ◽  
Long Distance ◽  
Landscape Level

scholarly journals Camelina (Camelina sativa L. Crantz) Crop Performance, Insect Pollinators, and Pollen Dispersal in the Northeastern US

2019 ◽  
Author(s):  
Richard Rizzitello ◽  
Chuan-Jie Zhang ◽  
Carol Auer
Keyword(s):  
Gene Flow ◽  
Honey Bees ◽  
Pollen Dispersal ◽  
Camelina Sativa ◽  
Genetically Engineered ◽  
Oilseed Crop ◽  
Crop Failure ◽  
Long Distance ◽  
Insect Visitation ◽  
Pollinating Insects

AbstractCamelina sativa (camelina) is an oilseed crop in the Brassicaceae that has been genetically engineered for the production of biofuels, dietary supplements, and other industrial compounds. Cultivation in North America is both recent and limited, so there are gaps in knowledge regarding yield, weed competition, and pollen-mediated gene flow. For these experiments, camelina ‘SO-40’ was grown for three years without weed control. Spring-sown camelina was harvested at 80-88 days with ∼1200 growing degree days (GDD) with yields of 425-508 kg/hectare. Camelina yields were the same with or without weeds, showing competitive ability in low-management conditions. Crop failure in 2015 was associated with delayed rainfall and above-average temperatures after seeding. Camelina flowers attracted pollinating insects from the Hymenoptera, Diptera, Lepidoptera, and Coleoptera. Hymenoptera included honey bees (Apis melifera), mining bees (Andrenidae), sweat bees (Halictidae), bumble bees (Bombus spp.) and leaf cutter bees (Megachilidae). Insect visitation on camelina flowers was associated with modest increases in seed yield. Honey bees comprised 28-33% of all pollinators and were shown to carry camelina pollen on their legs. Air sampling showed that wind-blown pollen was present at low concentrations at 9 m beyond the edges of the field. These experiments demonstrated for the first time that camelina pollen dispersal could occur through honey bees or wind, although bee activity would likely be more significant for long-distance gene flow.

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