The Maintaince Of Heterostylous In Limonium Kaschgaricum And Its Influencing Factors

Heterostyly is a heritable style polymorphism controlled by genes in which a species has two(distyly)or three(tristyly)floral morphs that exhibit reciprocal herkogamy between female and male sexual organs(stigmas and anthers)of different morph types,diallelic incompatibility system and a suit of ancillary polymorphism including pollen and stigma morphology and physiology.Heteromorphicstyle has been widely concerned as a typical model breeding system and is believed to promote accurate pollen transmission,reduce interference between male and female functions,and avoid self-pollination.The population structure,the polymorphism of style,the accessory polymorphism of pollen and stigma morphology and the heteromorphic incompatibility system have always been the reaseach focus of evolutionary ecologists.Limonium kaschgaricum is a perennial herb of Plumbaginacea,which is only distributed in xinjiang in China.According to the preliminary investigation,this plant is mostly distributed sporadically in the harsh arid desert environment.The investigated population has partical characteristics of dimorphic style,which is different from the typical dimorphic style.So,we studied population structure,floral traits related to the distylous syndrome,assessed the role of long-or short-tongued pollinators,natural female fertility of morphs and self-incompatibility system to explore the factors affecting the maintenance of heterostylys.The results are as follows:(1)The KC populations mainly composed of L-morph,S-morph,and some atypical morph PL,PS H morph with pistils slightly higher or lower than the stamens or equal height.Reciprocity indices at both the lower(R_L)and upper level(R_H)are 0.0113 and0.022 respectively,and show strong reciprocity between L–morph and S-morph in which the low level sex organs have higer reciprocity.The morph ratio of L–morph and S-morph is 1.35:1,deviating from isoplethic ratio(1:1).But the morph ratio of cop and pap.is 1.21:1 without significant deviation from isoplethic ratio(1:1).(2)The phenophase are various in different habitats and years.Blooming starts in late April in KC population,and the population flowering period lasted for about 45d.For a single flower,the petals usually unfolded at about 8:00 on sunny days,remained open for about 1–2 d.Numerous flowers open simultaneously in the same plant.(3)There were no significant differences in whole floral characteristic parameters,such as the corolla diameter,calyx length,corolla tube length among of S-morph,L-morph,and H-morph.The pollen surface ornamentation and stigma papilla shape are dimorphism in which S-morph flower appears stigma with papillae and pollen outer wall with decoration polygon,fine mesh and stigma of L-morph owning corn grain shap and pollen outer wall with decoration for the rough network.(4)KC population pollinators are composed of long-tongued and short-tongued pollinator.There were significant differences in occurrence period and visiting frequency.At the initial flowering stage,the main pollinator was the hoverfly,and the pollinator frequency was 0.068±0.023(visits/flower/hour)in the middle and late stage,the main pollinators were short-tongued pollinator with visiting frequency of 0.092±0.02(visits/flower/hour)and long-tongued pollinators with visiting frequency of 0.92±0.07(visits/flower/hour)respectively.The visiting frequency of long-tongued insects was significantly higher than that of short-tongued insects.In the early and middle flowering period long-tongued insects are main pollinator.The pollen transfer between high organs was significantly greater than that between low organs.That is,there was asymmetric pollen flow in the population.There is similar pollen transfer between the higher and lower organ levels when long-tongued insects apperaing.The pollinator variety,behavior,visiting frequency were seriously affected pollen transfer and the progeny fitness of different floral morphs.The long-tongued insects are the most effective pollinator for maintaining the population dimorphism of Limonium kaschgaricum.(5)Limonium kaschgaricum has strict heteromorphic incompatibility.The fruit-set was different in different habitat population.However,there was no significant difference in natural seed setting between different floral morphs in the same population.The natural seed setting rate in the middle and late period of fruit set was significantly higher than that in the early period.Artificial self/intramorph pollination seed setting rate was 0.H-morph was no reciprocal herkogamy with other morphs,however,there was no significant difference between the setting rate and other morphs.In the absence of reciprocal herkogamy between the high of pistils and stamens,the ancillary polymorphisms of stigma and pollen morphology may promotes disassortative mating,and maintained the floral-morph ratio in population.(6)The difference of seed setting rate of Limonium kaschgaricum in different habitats and flowering stages reflects the great influence of environmental factors on the population.The KC population studied was located at the foot of the south slope of Tianshan mountain.The windy,dry and hot weather during the flowering period led to a small number of flower visitors and instability,and the species of long-tongued insects were single.All these become the biggest factor restricting the fitness of population reproduction and may be the main driving force of the evolution of heterostyly.