scholarly journals Experimental evidence for selection against hybrids between two interfertile red oak species

2018 ◽  
Vol 67 (1) ◽  
pp. 106-110
Author(s):  
Oliver Gailing ◽  
Ruhua Zhang
Keyword(s):  
Reproductive Isolation ◽  
Low Frequency ◽  
Natural Hybridization ◽  
F1 Hybrids ◽  
Pure Species ◽  
Contact Zones ◽  
Genetic Assignment ◽  
Environmental Selection ◽  
Adult Trees ◽  
Quercus Ellipsoidalis

Abstract Reproductive isolation between related oak species within one taxonomic section is incomplete. Even though pre- and post­zygotic isolation mechanisms have been described for interfer­tile oak species, natural hybridization is common in contact zones between related oaks. The apparent restriction of inter­specific hybrids between ecologically divergent species to intermediate environments in contact zones suggests postzy­gotic isolation via environmental selection against hybrids in parental environments. Overrepresentation of hybrids in seeds as compared to adult trees provides additional indirect evi­dence for selection against hybrids. Here, we used genetic assignment analyses in progeny obtained from a sympatric stand of Quercus rubra and Quercus ellipsoidalis, two interfertile species with different adaptations to drought, to characterize the number of hybrids and “pure” species in the non-germinated acorns and in seedlings. The occurrence of 43.6 % F1 hybrids and introgressive forms among the non-germinated acorns and their very low frequency in the seedlings (9.3 %) is to our knowledge the first direct evidence for early selection against hybrids in oaks possibly as result of genetic incompatibilities. Additionally, we found a signature of positive selection on EST-SSR PIE200 in Q. rubra which needs further confirmation. These results contribute to our under­standing of reproductive isolation and divergence between interfertile oak species with different ecological adaptations.

scholarly journals Natural hybridization between two butterfly bushes in Tibet: dominance of F1 hybrids promotes strong reproductive isolation   

2020 ◽  
Author(s):  
Rongli Liao ◽  
Weibang Sun ◽  
Yongpeng Ma
Keyword(s):  
Reproductive Isolation ◽  
Parental Species ◽  
Morphological Characters ◽  
Natural Hybridization ◽  
Hybrid Origin ◽  
F1 Hybrids ◽  
Evolutionary Significance ◽  
Sympatric Populations ◽  
Hybrid Species ◽  
Intergenic Spacers

Abstract Background: F1 hybrids acting as a bridgehead for producing later generation hybrids can have evolutionary significance through strengthening reproductive isolation or facilitating gene flow between parental species, depending on whether backcrossing can occur. It had been suggested that the Tibetan plant Buddleja wardii was a hybrid species between B. alternifolia and B. crispa based on their sympatric distributions and the morphological characters in last century. Till now however, we still have limited evidence to prove key issues to B. wardii, like if it is of hybrid origin indeed and whether it is currently a true hybrid species already.Results: In the present study, two sympatric populations of these three taxa were examined and compared using four nuclear genes and three chloroplast intergenic spacers, as well as with 10 morphological characters. Our results suggest that at both sites B. × wardii was likely to be a hybrids between B. alternifolia and B. crispa, and moreover, most of the hybrids present were confirmed to be F1s. This was further supported by morphology as no transgressive characters were detected. B. crispa was found to be the maternal parent in one population (BH), while in the second population (TJ), it was difficult to distinguish the hybridization direction due to shared haplotypes of cpDNA between B. alternifolia and B. crispa. Conclusions: These results provide evidence that the natural hybrids between B. alternifolia and B. crispa mainly comprise F1 hybrids, which have subsequently been given the name B. wardii. The F1 hybrids have also contributed to strong reproductive isolation between parental species.

scholarly journals Natural Hybridization between Two Butterfly Bushes in Tibet: Dominance of F1 Hybrids Promotes Strong Reproductive Isolation

2020 ◽  
Author(s):  
Rongli Liao ◽  
Weibang Sun ◽  
Yongpeng Ma
Keyword(s):  
Reproductive Isolation ◽  
Parental Species ◽  
Morphological Characters ◽  
Natural Hybridization ◽  
Hybrid Origin ◽  
F1 Hybrids ◽  
Evolutionary Significance ◽  
Sympatric Populations ◽  
Hybrid Species ◽  
Intergenic Spacers

Abstract Background: F1 hybrids acting as a bridgehead for producing later generation hybrids can have evolutionary significance through strengthening reproductive isolation or facilitating gene flow between parental species, depending on whether backcrossing can occur. It had been suggested that the Tibetan plant Buddleja wardii was a hybrid species between B. alternifolia and B. crispa based on their sympatric distributions and the morphological characters in last century. Till now however, we still have limited evidence to prove key issues to B. wardii, like if it is of hybrid origin indeed and whether it is currently a true hybrid species already.Results: In the present study, two sympatric populations of these three taxa were examined and compared using four nuclear genes and three chloroplast intergenic spacers, as well as with 10 morphological characters. Our results suggest that at both sites B. × wardii was likely to be a hybrids between B. alternifolia and B. crispa, and moreover, most of the hybrids present were confirmed to be F1s. This was further supported by morphology as no transgressive characters were detected. B. crispa was found to be the maternal parent in one population (BH), while in the second population (TJ), it was difficult to distinguish the hybridization direction due to shared haplotypes of cpDNA between B. alternifolia and B. crispa. Conclusions: These results provide evidence that the natural hybrids between B. alternifolia and B. crispa mainly comprise F1 hybrids, which have subsequently been given the name B. wardii. The F1 hybrids have also contributed to strong reproductive isolation between parental species.

Natural hybridization between an outcrossing and a selfingPhlox (Polemoniaceae): The maternal species of F1 hybrids

1999 ◽  
Vol 218 (1-2) ◽  
pp. 153-158 ◽  
Author(s):  
Carolyn J. Ferguson ◽  
Donald A. Levin ◽  
Robert K. Jansen
Keyword(s):  
Natural Hybridization ◽  
F1 Hybrids

scholarly journals Ecological divergence in sympatry causes gene misregulation in hybrids

2019 ◽  
Author(s):  
Joseph A. McGirr ◽  
Christopher H. Martin
Keyword(s):  
Gene Expression ◽  
Reproductive Isolation ◽  
Differentially Expressed ◽  
F1 Hybrids ◽  
Adaptive Divergence ◽  
Lower Hybrid ◽  
Hybrid Fitness ◽  
Hybrid Gene ◽  
San Salvador ◽  
Ecological Selection

AbstractEcological speciation occurs when reproductive isolation evolves as a byproduct of adaptive divergence between populations. However, it is unknown whether divergent ecological selection on gene regulation can directly cause reproductive isolation. Selection favoring regulatory divergence between species could result in gene misregulation in F1 hybrids and ultimately lower hybrid fitness. We combined 58 resequenced genomes with 124 transcriptomes to test this hypothesis in a young, sympatric radiation of Cyprinodon pupfishes endemic to San Salvador Island, Bahamas, which consists of a dietary generalist and two novel trophic specialists – a molluscivore and a scale-eater. We found more differential gene expression between closely related sympatric specialists than between allopatric generalist populations separated by 1000 km. Intriguingly, 9.6% of genes that were differentially expressed between sympatric species were also misregulated in their F1 hybrids. Consistent with divergent ecological selection causing misregulation, a subset of these genes were in highly differentiated genomic regions and enriched for functions important for trophic specialization, including head, muscle, and brain development. These regions also included genes that showed evidence of hard selective sweeps and were significantly associated with oral jaw length – the most rapidly diversifying skeletal trait in this radiation. Our results indicate that divergent ecological selection in sympatry can cause hybrid gene misregulation which may act as a primary reproductive barrier between nascent species.SignificanceIt is unknown whether the same genes that regulate ecological traits can simultaneously contribute to reproductive barriers between species. We measured gene expression in two trophic specialist species of Cyprinodon pupfishes that rapidly diverged from a generalist ancestor. We found genes differentially expressed between species that also showed extreme expression levels in their hybrid offspring. Many of these genes showed signs of selection and have putative effects on the development of traits that are important for ecological specialization. This suggests that genetic variants contributing to adaptive trait divergence between parental species negatively interact to cause hybrid gene misregulation, potentially producing unfit hybrids. Such loci may be important barriers to gene flow during the early stages of speciation, even in sympatry.

Morphology and fitness components of wild × crop F1 hybrids of Sorghum bicolor (L.) in Ethiopia: implications for survival and introgression of crop genes in the wild pool

2013 ◽  
Vol 11 (3) ◽  
pp. 196-205 ◽  
Author(s):  
Asfaw Adugna ◽  
Endashaw Bekele
Keyword(s):  
Risk Assessment ◽  
Natural Hybridization ◽  
Relative Fitness ◽  
F1 Hybrids ◽  
Transgenic Crop ◽  
Fitness Components ◽  
Crop Species ◽  
In The Wild ◽  
Sorghum Bicolor L ◽  
Made In

Natural hybridization between wild/weedy and crop species often results in rare hybrids, which can be more weedy and difficult to control. Moreover, the advent of transgenic crop plants raises questions of biosafety risk assessment on the consequences of rare hybrids with possible fitness enhancing genes on the environment. This study aimed at measuring the fitness components of wild–crop sorghum hybrids for various juvenile survival and adult morphological and fertility characters as part of the risk assessment of transgenic sorghum in Africa where the crop was believed to have first domesticated and serves as the major staple. Out of a pool of hybrids made in 2010 from 23 wild sorghum accessions and two released cultivated sorghum varieties using hand emasculation techniques, seven were selected for the field study of their fitness components in 2011. The study confirmed that crop–wild hybrids of sorghum are fertile. Two approaches were followed (relative fitness and mid-parent heterosis) which showed that most of the hybrids were as fit as their wild parents, and in some cases they showed mid-parent heterosis for the measured traits. The results of this study highlighted a potential risk that hybrids carrying crop genes (including herbicide resistance transgenes) could pose because they could be more weedy than their wild/weedy parents if transgenic sorghum is deployed in regions where the wild and cultivated sorghum populations coexist, such as in Ethiopia and in other parts of Africa.

scholarly journals Gene Flow Between Introduced and Native Eucalyptus Species: Morphological Analysis of Tri-Species and Backcross Hybrids Involving E. nitens

2007 ◽  
Vol 56 (1-6) ◽  
pp. 127-133 ◽  
Author(s):  
C. Barbour ◽  
B. M. Potts ◽  
R. E. Vaillancourt
Keyword(s):  
Gene Flow ◽  
Second Generation ◽  
Current Work ◽  
F1 Hybrids ◽  
Morphological Identification ◽  
Eucalyptus Species ◽  
Pure Species ◽  
Backcross Hybrids ◽  
In The Wild ◽  
Species Hybrids

Summary Morphometric analyses were conducted on second-generation tri-species and backcross hybrids in Eucalyptus. These hybrids were all produced using pollen from two E. nitens x cordata F1 hybrids and controlled pollination techniques. Tri-species hybrids were created with E. gunnii, E. ovata and E. viminalis as females, while backcrosses were produced with E. cordata. Multivariate analysis of seedling characteristics indicated that eighty percent of the backcross hybrids fell within the morphological range of E. cordata. All three cross combinations of the tri-species hybrids were biased away from E. nitens and towards their maternal parent and E. cordata. The inclusion of data for first-generation (F1) hybrids between the pure parental species in the current work showed the F1’s to be easily distinguishable from pure species, compared to second-generation hybrids. The use of morphology for detecting second-generation hybridisation involving exotic plantation species and native eucalypt populations will therefore be unreliable, and identifies a need for preventing second-generation hybrids from establish in the wild. The current work, nevertheless, provides further demonstration of the effectiveness of morphological identification of F1 hybrids. The easy recognition of F1 hybrids will be useful in identifying sites and species at risk of exotic gene flow and enable the development of weeding programs that focus on removing exotic hybrids in the wild.

Patterns of Inheritance in the Bowing Display and Associated Behaviour of Some Hybrid Streptopelia Doves

Behaviour ◽  
1970 ◽  
Vol 36 (3) ◽  
pp. 187-214 ◽  
Author(s):  
S.J.J.F. Davies
Keyword(s):  
The Other ◽  
F1 Hybrids ◽  
Characteristic Form ◽  
Pure Species ◽  
F1 Hybrid ◽  
Cine Film ◽  
F2 Generation ◽  
Species Hybrids ◽  
Relative Variability

AbstractThe bowing display of Streptopelia doves was studied in captive individuals of five species at Madingley, Cambridge, England from 1961 to 1964. The five species were S. roseogrisea-(risoria) (barbary), S. decaocto (collared), S. turtur (turtle), S. chinensis (necklace) and S. senegalensis (senegal). F1 hybrids were bred between the barbary and the other four species and single males of each of the F1 necklace x collared and senegal x turtle were also observed. F2 generation birds of the collared x barbary F1 hybrid, as well as some backcrossed birds were included in the study. Bowing displays were usually given only by male doves when close to another dove. The form of the bowing display differed from species to species and exhibited a typical intensity in each species. Each hybrid also had a bowing display of characteristic form. The ciné film showed that there was variation in form between the bowing cycles of any one bout, both in the pure species and in the hybrids. This variation could not be adequately described from the films taken in this study. The rate of bowing of each species was constant and differed from that of every other species. Hybrids also exhibited a typical intensity in this character. There was much more intra-specific and intra-hybrid variaton in the timing of individual movements within bowing cycles in a bout than in the timing of the bowing cycle as a whole. The relative variability of the different elements could be ranked, and in all species and hybrids studied the timing of the total cycle tended to be least variable and that of the pause at the top of the bow most variable. The frequencies with which bowing displays and kah calls were given under standard conditions, were measured, and provided two other behavioural characters whose pattern of inheritance could be studied. Three patterns of inheritance were found in each of these behaviour patterns of the F1 hybrids. In some cases the behaviour was intermediate between that of the two parents, in others it approximated the behaviour of one parent closely and in others again the hybrid's behaviour exceeded the range of either parent.

Contrasting Success of Natural Hybridization in Two Eucalyptus Species Pairs

1980 ◽  
Vol 28 (2) ◽  
pp. 167 ◽  
Author(s):  
DW Drake
Keyword(s):  
Principal Component ◽  
Flowering Phenology ◽  
Natural Hybridization ◽  
F1 Hybrids ◽  
Hybrid Population ◽  
Eucalyptus Species ◽  
Major Barrier ◽  
Species Pairs ◽  
Plant Hybridization ◽  
Hybrid Number

A morphological study with univariate and principal component analyses of mature tree and open-pollinated seedling populations shows that natural hybridization is occurring between Eucalyptus melanophloia and E. crebra, and E. populnea and E. crebra (subgenus Symphyomyrtus, section Adnataria). The level of successful hybridization in these two systems, where fundamental genetic (reproductive) and ecological (habitat and spatial) barriers are absent, is examined. Within the ecotone, hybrids between E. melanophloia and E. crebra are about one-fifth as frequent as those between E. populnea and E. crebra. Analyses of the phenotype/genotype compositions of the hybrid populations, the patterns of segregation, and outcrossing frequencies between the species pairs indicate the level of development of the hybrid populations. All E. melanophloia × E. crebra hybrids appear to be F1 hybrids. In contrast, the E.populnea x E. crebra hybrid population attains a much higher level of development in terms of both hybrid number and genotypic complexity. Flowering phenology is a major barrier to E. melanophloia × E. crebra hybrid formation compared with the other hybrids, although it is considered an incomplete barrier and alone may not explain the diversity of hybrid success which occurs.A theory of plant hybridization which incorporates the concept of hybridization success is presented and discussed in relation to the two hybridizing systems, as a basis for further investigating the mechanisms involved.

scholarly journals Isolation and re-connection: the formation of a ring-shaped speciation continuum in an odorous frog (Odorrana margaretae)

2021 ◽  
Author(s):  
Guannan Wen ◽  
Jinzhong Fu
Keyword(s):  
Reproductive Isolation ◽  
Sichuan Basin ◽  
Western China ◽  
Hybrid Zones ◽  
Distributional Pattern ◽  
Contact Zones ◽  
The North ◽  
Population Structure Analysis ◽  
Speciation Continuum ◽  
Glacial Expansion

The Green Odorous Frog (Odorrana margaretae) around the Sichuan Basin of western China displays a ring-shaped distributional pattern and possesses multiple replicate contact zones between lineages at various levels of differentiation. To understand its unique speciation history and mechanisms, we obtained 1,540 SNPs from 29 populations and 227 individuals using ddRAD sequencing. Population structure analysis revealed three groups within the species: The West, the North & South, and the East groups. These groups were initially isolated at ~2.03 million years ago, and subsequent post-glacial expansion produced the current ring-shaped distribution around Sichuan Basin with three contact zones. Hybridization in those zones involved lineages with different levels of divergence and produced greatly different outcomes. Both the hybrid zones at southwest (S-W) and southeast (E-NS) of the Basin have extensive admixture and less barrier effect. Consequently, the southern region has the highest genetic diversity and becomes an ‘evolutionary melting pot’. In contrast, the hybrid zone at northwestern corner (N-W), which resembles the overlap zone between two expansion terminals of a ring species, has limited admixture with a narrow geographic cline, suggesting partial reproductive isolation between the northern and western populations. The three hybrid zones likely resemble three time points along a speciation continuum; while both E-NS and S-W hybrid zones are merging, the N-W zone may have passed the ‘tipping point’ and is destined for a complete reproductive isolation over time.

scholarly journals Pure species discriminate against hybrids in the Drosophila melanogaster species subgroup

2020 ◽  
Author(s):  
Antonio Serrato-Capuchina ◽  
Timothy D. Schwochert ◽  
Stephania Zhang ◽  
Baylee Roy ◽  
David Peede ◽  
...  
Keyword(s):  
Drosophila Melanogaster ◽  
Gene Flow ◽  
Parental Species ◽  
Cuticular Hydrocarbon ◽  
F1 Hybrids ◽  
Sexual Attractiveness ◽  
Pure Species ◽  
Species Pairs ◽  
Fertile Hybrids ◽  
Drosophila Melanogaster Species Subgroup

ABSTRACTIntrogression, the exchange of alleles between species, is a common event in nature. This transfer of alleles between species must happen through fertile hybrids. Characterizing the traits that cause defects in hybrids illuminate how and when gene flow is expected to occur. Inviability and sterility are extreme examples of fitness reductions but are not the only type of defects in hybrids. Some traits specific to hybrids are more subtle but are important to determine their fitness. In this report, we study whether F1 hybrids between two species pairs of Drosophila are as attractive as the parental species. We find that in both species pairs, the sexual attractiveness of the F1 hybrids is reduced and that pure species discriminate strongly against them. We also find that the cuticular hydrocarbon (CHC) profile of the hybrids is intermediate between the parental species. Perfuming experiments show that modifying the CHC profile of the hybrids to resemble pure species improves their chances of mating. Our results show that behavioral discrimination against hybrids might be an important component of the persistence of species that can hybridize.

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