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。

Pollinator functional groups and their pollen transfer efficiency in heterostylous Limonium kaschgaricum (Plumbaginaceae)

Aims Heterostyly is a heritable style polymorphism controlled by genes, which was emphasized by Darwin as an adaptation to promote accurate pollen transfer between floral morphs by depositing two types of pollen on different parts of insect bodies. This hypothesis has received much attention, but little is known about the effects of different pollinator groups on the reproductive success of different morphs in some populations with large variation in floral morphs composition and unstable pollination system.Methods We investigated the floral morph composition, morph ratio, pollinator types and pollination efficiencies inLimonium kaschgaricum which distributed in the south slope of Tianshan in Xinjiang, China, a heterostylous population with coexistence of homostylyous morph, in order to understand the function of different pollinator groups and their influence on the fruit set of different morphs and floral morph ratios.Important findings Results showed that: 1) The population mainly composed of L-morph, S-morph flowers with reciprocal placement of anthers and stigmas and H-morph flowers with equal pistils and stamens height. There were no differences in corolla diameter, corolla tube length and pollen production among morphs, but the morphology of pollen ornamentation and stigma mastoid cells were dimorphic. H-morph flowers were identical with L- (or S-) morph flowers in morphology of pollen ornamentation and stigma mastoid cells. 2) The results of heteromorphic incompatibility test showed that intramorph and self-pollination were incompatible in all floral morphs. The intermorph pollination was compatible when pollen ornamentation and stigma mastoid cells were hetermorphic, otherwise it was incompatible. 3) There were two types of pollinator functional groups, long and short-tongued. But they did not appear synchronously, short-tongued insects appeared in early and medium stages of flowering, and long-tongued insects appeared in the later flowering period. When the short-tongued insects were main pollinators at the early and medium stages of flowering, the number of intermorph pollen on stigma of long- and homo-styled morphs was significantly higher than that of short-styled morphs. The intermorph pollen transfer efficiency between high-sexual organs were higher than between low sexual organs. In the later stage of flowering, when long-tongued insects were main pollinators, there were no differences in the intermorph pollen loads on stigma of long- and short-styled morphs, and the intermorph pollen transfer proficiency between high-sexual organs were symmetrical with low sexual organs. At the same time, the fruit sets in different flowering stages were obviously different. 4) Long- and short-tongued insects have significantly different pollen transfer efficiencies, the short-tongued insects only transfer pollen between high sex organs, were low efficient pollinators with low visiting frequency and intermorph pollen transfer proficiency. However, long-tongued insects were efficient pollinators for all floral morphs, and were high efficient pollinators with high visiting frequency and intermorph pollen transfer proficiency. The unstable pollination system caused by periodical appearance of long-tongued insects may make the short-tongued insects become the main driving force causing floral morphs variation and S-morph flowers may suffer greater driving force. H-morph flowers may exist as an alternative floral morph in this unstable pollination system due to overcoming the drawback of sunken stigma.