杓兰属三稜组蝇类欺骗性传粉系统进化机制研究

Charles Darwin used orchid flowers as model systems to explain the evolution of functional morphology and adaptations. However, Darwin ignored the concept of pollination-by-deceit, in which floral stimuli attracts pollinators but the flower fails to reward the pollinator. Recent theories insist that floral mimesis or deception appears to drive speciation in the majority of lineages within the terrestrial Orchidaceae. Historically, the genus Cypripedium has been regarded as a model lineage of nonrewarding orchid flowers, the majority of species studied, to date, are bee-pollinated. However, recent studies indicate that, at least, five Cypripedium species found in the southwestern mountains of China are pollinated by small flies (Microdoptera) exploiting a suite of attractant characters known as myophily. Previously, we described a new mode of deceptive pollination in C. fargesii which requires fungus-eating (mycophagic) flies for pollination. The blackish hairy spotted leaves combine with the floral pigmentation patttern and musty floral scent lure flies that would feed on the fungal exudates of infected vegetation. Theoretically, the leaf and flower mimesis of fungus-infected foliage probably represents a "bridge" between generalist food mimesis, in most Cypripedium spp., and full mimicry of fungal fruiting bodies (sporocarps). Based on molecular evidence, C. fargesii has three-five sister species so closely related that they are all now placed in Sect. Trigonopedia. All of these species have similar pirmentation patterns on their leaves and flowers as C. fargesii. Further field and lab work is required to show whether the same mode of deceptive pollination persists throughout Sect. Trigonopedia? Do all species attract the same fly species? We propose a morphometric, quantitative and biochemical study to compare pollination modes within the Trigonopedia lineage to determine evolutionary trends. This comparative approach will focus on populations of C. fargesii, and its most easily located sister species, C. margaritaceum and lichiangense. Their floral functional morphologies, breeding systems, pollinators and scent molecules must be compared via modern, field/lab techniques and biometric programs. Research subdivides into three, overlapping programs: 1) Analyze, compare and define the visual and olfactory signal systems in this novel mode of mimesis in this lineage. 2) Test whether the mimesis of fungus-infected foliage in C. fargessi parallels leaf patterns and vestiture in the sister species or, if not, how do the pollination syndromes vary to deceive different insects? 3) Compare and analyze variation of pollination systems in Trigonopedia to reveal and interpretate evolutionary pathways; 4) Provide life-history data to help formulate conservation strategies to better protect these endangered orchids to maintain surviving, self-perpetuating populations from viable seed.

欺骗性传粉是兰科植物多样性形成的重要原因之一。杓兰属（Cypripedium L.）是研究兰科植物欺骗性传粉系统进化的模式类群。大部分杓兰属植物为典型的蜂类传粉，拟态系统为泛化的食源性欺骗。杓兰属三稜组植物在我国西南山地这一分布中心其传粉者出现了蜂类向蝇类的转变。最近申请者对三棱组的毛瓣杓兰（C. fargesii）研究发现该植物带斑点的叶片和花气味拟态被枝孢菌感染的叶片，从而达到诱骗蝇类传粉的目的，这是一种全新的拟态方式。然而，与毛瓣杓兰具有相似表型的近缘种的传粉系统尚不清楚，这种拟态现象是否同样存在需要进一步验证。本项目选取毛瓣杓兰及其近缘种斑叶杓兰（C. margaritaceum）和丽江杓兰（C. lichiangense）作为研究对象开展传粉系统进化研究，进一步深化对这一特有的拟态机制的认识；揭示毛瓣杓兰近缘种的传粉式样和拟态机制；为兰科植物的保护提供重要依据。

项目负责人对三稜组的毛瓣杓兰（Cypripedium fargesii）研究发现该植物带斑点的叶片和花气味拟态被枝孢菌感染的叶片，从而达到诱骗蝇类传粉的目的，这是一种全新的拟态方式。然而，与毛瓣杓兰具有相似表型的近缘种的传粉系统尚不清楚，这种拟态现象是否具有普遍性需要进一步验证。项目选取毛瓣杓兰及其近缘种作为研究对象开展传粉（繁育）系统的进化生态学研究，以进一步深化对这一新拟态机制的认识，同时为濒危兰科植物的保护提供科学依据。项目组对分布于云南的四种杓兰开展了详细的种群结构、开花结实动态、繁育系统、近交衰退、花粉-雌蕊互作的延迟受精、传粉昆虫观察和花气味收集与测定等研究。研究发现：1）由于近年来早春大旱，三种濒危兰科植物的种群都有下降趋势，特别是开花植株的数量在丽江分布的丽江杓兰和斑叶杓兰的居群下降明显；2）丽江杓兰和斑叶杓兰连续6年野外结实率为零，可能与花期推迟从而与传粉昆虫活动期不匹配有关，野外种群面临极高的灭绝风险；3）延迟受精和延迟果实成熟使推迟开花的植株在冬季依然未完成生活史，也是导致其濒危的重要原因之一；4）三个种都是自交亲和，但是存在自交衰退，自然结实的果实都是来自于异花授粉，表明不可逆陷阱花结构有效促进异交；5）毛瓣杓兰的传粉昆虫与原来的发现一致，进一步证实了其传粉系统的特化性，研究发现有雌性昆虫产卵现象，表明产卵地拟态的存在与兜兰属存在平行进化，也说明拟态真菌感染植物组织向真菌拟态（产卵地拟态）的过渡是不稳定的；6）拟态真菌感染的植物组织在暖地杓兰中也存在。本研究证实了真菌拟态在杓兰属中的普遍性与特殊性。人为破坏、气候变化导致的花期推迟、延迟受精和延迟果实成熟等诸多因素导致这些濒危兰花的种群有高的局域灭绝的风险。