Unidirectional hybridization and reproductive barriers between two heterostylous primrose species in north-west Yunnan, China

Ma, Yongpeng; Xie, Weijia; Tian, Xiaoling; Sun, Weibang; Wu, Zhi‐Kun; Milne, Richard I.

doi:10.1093/aob/mct312

Cited by 33 publications

(47 citation statements)

References 79 publications

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“…Furthermore, the existence of F2 individuals indicated that the F1 hybrids were fertile, although they were not included in the sampling. Similar phenomena has been reported in heterostylous Primula (Ma et al ). The authors suggested that at least one F1 must have been present originally though it was not sampled.…”

Section: Discussionsupporting

confidence: 89%

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Reproductive isolation between sympatric sister species, Mussaenda kwangtungensis and M. pubescens var. alba

Luo

Duan

Yuan

et al. 2015

JIPB

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Reproductive isolation defines the biological species concept and plays a key role in the formation and maintenance of species. The relative contributions of different isolating stages has been suggested to be closely associated with phylogenetic relatedness. Few studies have focused on the relative contributions of pre- versus post-zygotic mechanisms, and even fewer have been conducted under strict phylogenetic frameworks. Pre- and post-zygotic reproductive isolation stages have been investigated in the sister species Mussaenda kwangtungensis and M. pubescens var. alba. The two species have partly overlapping distribution ranges and flowering times, while the principal pollinators differed strikingly for them, demonstrating strong pre-zygotic isolations. Natural hybrids were detected by simple sequence repeat markers and their maternal parents were identified based on chloroplast gene sequences. Five out of 81 individuals were suggested to be hybrids that fall into the categories F2, BC1, and BC2 by the NewHybrids analysis. Interspecific crossings resulted in significantly reduced fruit set and seed germination rates. Phylogenetic analysis revealed short Kimura-2-parameter distance between M. kwangtungensis and M. pubescens var. alba. These findings strongly supported the hypothesis that for species with a closer phylogenetic relationship, pre-zygotic isolation plays an important part in limiting gene exchange in sympatric areas.

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Section: Discussionsupporting

confidence: 89%

“…The authors suggested that at least one F1 must have been present originally though it was not sampled. Therefore, hybrid zones can exist without F1s if the original F1 has died and no others have been formed (Arnold et al ; Cruzan and Arnold ; Chung et al ; Ma et al ).…”

Section: Discussionmentioning

confidence: 99%

Reproductive isolation between sympatric sister species, Mussaenda kwangtungensis and M. pubescens var. alba

Luo

Duan

Yuan

et al. 2015

JIPB

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“…In vitro embryo rescue is commonly used to bypass endosperm failure and allows the production of viable hybrid plants, supporting that the endosperm is a major cause of interspecific seed inviability [18,19]. Interestingly, several reports converge on the unidirectional effects of hybridization on seed phenotypes in genera such as Primula or Kalanchoe [19,20] and unidirectional gene flow between species has been commonly observed in natural conditions [21][22][23].…”

Section: Introductionmentioning

confidence: 99%

Epigenetic mechanisms of postzygotic reproductive isolation in plants

Lafon‐Placette

Köhler

2015

Current Opinion in Plant Biology

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“…Due to the small sample size it is possible that this is an artifact, but it is also possible that certain other factors favor backcrossing to B. crispa in the wild. It is widely accepted that many types of pre- and post- zygotic barriers can act together to prevent hybridization and introgression [26–28]. Artificial pollination experiments only cover a small subset of these barriers.…”

Section: Discussionmentioning

confidence: 99%

“…Seed viability tests were carried out using an X-ray image system (MX-20-DC12, Faxitron, USA, [28]). It should be noted that seed numbers were counted after seed dispersal, as fruit ripeness is difficult to assess in Buddleja .…”

Section: Methodsmentioning

confidence: 99%

Natural hybridization and asymmetric introgression at the distribution margin of two Buddleja species with a large overlap

Liao

Gong

et al. 2015

BMC Plant Biol

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BackgroundNatural hybridization in plants is universal and plays an important role in evolution. Based on morphology it has been presumed that hybridization occurred in the genus Buddleja, though genetic studies confirming this assumption have not been conducted to date. The two species B. crispa and B. officinalis overlap in their distributions over a wide range in South-West China, and we aimed to provide genetic evidence for ongoing hybridization in this study.ResultsWe investigated the occurrence of hybrids between the two species at the southern-most edge of the distribution of B. crispa using five nuclear loci and pollination experiments. The genetic data suggest substantial differentiation between the two species as species-specific alleles are separated by at least 7–28 mutations. The natural hybrids found were nearly all F1s (21 of 23), but backcrosses were detected, and some individuals, morphologically indistinguishable from the parental species, showed introgression. Pollen viability test shows that the percentage of viable pollen grains was 50 ± 4 % for B. crispa, and 81 ± 2 % for B. officinalis. This difference is highly significant (t = 7.382, p < 0.0001). Hand cross-pollination experiments showed that B. crispa is not successful as pollen-parent, but B. officinalis is able to pollinate B. crispa to produce viable hybrid seed. Inter-specific seed-set is low (8 seeds per fruit, as opposed to about 65 for intra-specific pollinations), suggesting post-zygotic reproductive barriers. In addition, one of the reference populations also suggests a history of introgression at other localities.ConclusionsThe occurrence of morphologically intermediate individuals between B. crispa and B. officinalis at Xishan Mountain is unequivocally linked to hybridization and almost all examined individuals of the putative hybrids were likely F1s. Despite pollination experiments indicating higher chances for introgression into B. officinalis (hybrids only produced viable seed when crossed with B. officinalis), observed introgression was asymmetrical into B. crispa. This could be due to seeds produced by hybrids not contributing to seedlings, or other factors favoring the establishment of backcrosses towards B. crispa. However, further research will be needed to confirm these observations, as the small number of plants used for the pollination experiments could have introduced an artifact, for example if used individuals were more or less compatible than the species average, and also the small number of loci used could convey a picture of introgression that is not representative for the whole genome.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-015-0539-9) contains supplementary material, which is available to authorized users.

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Unidirectional hybridization and reproductive barriers between two heterostylous primrose species in north-west Yunnan, China

Cited by 33 publications

References 79 publications

Reproductive isolation between sympatric sister species, Mussaenda kwangtungensis and M. pubescens var. alba

Reproductive isolation between sympatric sister species, Mussaenda kwangtungensis and M. pubescens var. alba

Epigenetic mechanisms of postzygotic reproductive isolation in plants

Natural hybridization and asymmetric introgression at the distribution margin of two Buddleja species with a large overlap

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