What ecological factors favor the shift from distyly to homostyly? A study from the perspective of reproductive assurance

Aims Distyly is one of the most widespread floral polymorphisms pro-moting cross-fertilization.Evolutionary transition from obligate cross-fertilized distyly to predominantly self-fertilized homostyly is frequently documented in various groups.However,empirical stud-ies concerning the ecological factors connected with this transition are still lacking.Primula chungensis,suggested to be evolving from distyly to homostyly,provides an ideal model for the study of the ecological factors concerned with this transition.We study P.chun-gensis to understand if autonomous self-fertilization would provide reproductive assurance for the self-fertilized homo-styled morph in the field.Methods the incompatibility features of P.chungensis were tested with hand-pollination experiments.We compared the capacity of autonomous self-fertilization between the distylous and homo-styled morph of P.chungensis in the field by excluding the pollinators with bags.In addition,the degrees of herkogamy of some P.chungensis plants were between the short-styled and homo-styled morphs.these plants were studied to understand whether they were able to obtain greater reproductive assurance when the herkogamy in the flowers was reduced.Important Findings All three morphs of P.chungensis were highly self-and intra-morph compatible.the degree of herkogamy positively correlated with the capacity for autonomous self-fertilization.A negative correlation between the degree of herkogamy and the magnitude of pollen limitation was found,but no significant correlation was found between the degree of herkogamy and the contribution of cross-fertilization to overall fertilization.this study suggests that reducing the degree of herkogamy can significantly increase the reproductive assurance for a self-compatible plant.Our results provided evidence that the homo-styled morph of P.chungensis had the highest capacity for autonomous self-fertilization and the highest seed production in the field,because autonomous self-fertilization provided reproduct-ive assurance for the homo-styled morph.this may cause selection towards the transition from distyly to homostyly.

Characterization of 24 microsatellite markers in Primula chungensis(Primulaceae),a distylous-homostylous species,using MiSeq sequencing

Primula chungensis is a species with considerable floral and mating-system variation,including distylous(outcrossing),homostylous(selfing) and mixed populations that contain both outcrossing and selfing forms.We isolated 24 microsatellite markers from P.chungensis using Illumina Mi Seq sequencing.Polymorphism and genetic diversity were then measured based on a sample of 24 individuals from a natural population in southern Tibet.All loci were polymorphic with the number of alleles per locus ranging from 2 to 4.The observed and expected heterozygosity ranged from 0 to 1 and 0.219 to 0.708,respectively.The microsatellite markers we have identified will serve as valuable tools for the investigation of the population genetic structure and phylogeography of P.chungensis and will inform models of the evolutionary history of mating systems in the species.

异型花柱植物喀什补血草的传粉者功能群与花粉转移效率

异型花柱是受遗传控制的花柱多态现象,被达尔文认为是植物通过在传粉者体表不同部位滞落花粉以促进型间花粉准确传递的一种适应。该现象虽已受到广泛关注,但在一些花型变异较大且不稳定的传粉系统中,不同传粉者对各花型繁殖所产生的影响仍知之甚少。该研究以分布于新疆天山南坡的一个有同长花柱共存的异型花柱植物喀什补血草(Limonium kaschgaricum)种群为研究对象,对其花型构成及频率、传粉者及花粉转移效率等进行了调查分析。结果表明:1)种群中除了存在雌/雄蕊长度交互对应的长(L)/短(S)花柱型花外,还有雌/雄蕊同长的花(H型),且各花型花的花冠口直径、花冠筒长及花粉量等参数间无差异,但花粉纹饰和柱头乳突细胞形态具二型性。其中, H型花的花粉和柱头形态与L型花(或S型花)的一致。2)花型内和自花授粉均不亲和;型间授粉时,花粉和柱头形态不同的花型间亲和,反之不亲和。3)种群内存在长/短吻两类传粉昆虫。在以短吻传粉者为主的盛花初、中期,L和H型花柱头上的异型花粉数均显著高于S型花的,且L和S型花高位性器官间的异型花粉传递效率高于低位性器官间的;而在以长吻传粉者为主的盛花后期, L和S型花的柱头间异型花粉数无显著差异,且高/低位性器官间具有相同的异型花粉转移效率;与传粉者出现时期相对应的、在花期不同阶段开放花的结实率也明显不同。4)长/短吻昆虫具明显不同的传粉功能,短吻昆虫只能对L和H型花进行有效传粉,且访花频率和型间花粉转移效率较低,为低效传粉者;而长吻昆虫对各花型均能有效传粉,具高的访花频率和型间花粉转移效率,为高效传粉者。因为长吻昆虫的阶段性出现所形成的不稳定传粉系统,使低效的短吻昆虫可能会成为种群中花型变异的驱动力,并使S型花受到更大的选择压力。H型花克服了柱头缩入的弊端,可能会成为不稳定传粉系统下的一个替代花型而持续存在。