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

文献类型： 外文期刊

作者： Ma, Yongpeng 1 ; Xie, Weijia 2 ; Tian, Xiaoling 1 ; Sun, Weibang 1 ; Wu, Zhikun 1 ; Milne, Richard 3 ;

作者机构： 1.Chinese Acad Sci, Kunming Inst Bot, Kunming Bot Garden, Kunming 650201, Peoples R China

2.Yunnan Acad Agr Sci, Flower Res Inst, Kunming 650201, Peoples R China

3.Univ Edinburgh, Inst Mol Plant Sci, Edinburgh EH9 3JH, Midlothian, Scotland

关键词： Unidirectional hybridization;reproductive barriers;F1 formation primrose;Primula heterostyly

期刊名称：ANNALS OF BOTANY （ 影响因子：4.357； 五年影响因子：5.488 ）

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收录情况： SCI

摘要： Heteromorphy in flowers has a profound effect on breeding patterns within a species, but little is known about how it affects reproductive barriers between species. The heterostylous genus Primula is very diverse in the Himalaya region, but hybrids there have been little researched. This study examines in detail a natural hybrid zone between P. beesiana and P. bulleyana. Chloroplast sequencing, AFLP (amplified fragment length polymorphism) markers and morphological comparisons were employed to characterize putative hybrids in the field, using synthetic F(1)s from hand pollination as controls. Pollinator visits to parent species and hybrids were observed in the field. Hand pollinations were conducted to compare pollen tube growth, seed production and seed viability for crosses involving different morphs, species and directions of crossing. Molecular data revealed all hybrid derivatives examined to be backcrosses of first or later generations towards P. bulleyana: all had the chloroplast DNA (cpDNA) of this species. Some individuals had morphological traits suggesting they were hybrids, but they were genetically similar to P. bulleyana; they might have been advanced generation backcrosses. Viable F(1)s could not be produced with P. bulleyana pollen on P. beesiana females, irrespective of the flower morphs used. Within-morph crosses for each species had very low (10 ) seed viability, whereas crosses between pin P. bulleyana (female) and pin P. beesiana had a higher seed viability of 30 . Thus genetic incompatibility mechanisms back up mechanical barriers to within-morph crosses in each species, but are not the same between the two species. The two species share their main pollinators, and pollinators were observed to fly between P. bulleyana and hybrids, suggesting that pollinator behaviour may not be an important isolating factor. Hybridization is strongly asymmetric, with P. bulleyana the only possible mother and all detected hybrids being backcrosses in this direction. Partial ecological isolation and inhibition of heterospecific pollen, and possibly complete barriers to F-1 formation on P. beesiana, may be enough to make F-1 formation very rare in these species. Therefore, with no F-1 detected, this hybrid zone may have a finite life span as successive generations become more similar to P. bulleyana.

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