Abstract:

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.

Key words: Limonium kaschgaricum, heterostyly, pollinator functional groups, pollen transfer proficiency, homostylyous morph