Specificity and mutual dependency of the orchid-euglossine bee interaction

Seasonal and geographic relationships, and host pollinator specificities are examined for indications of interdependency in the orchid-euglossine bee interaction. The orchids are dependent on the bees for pollination, and their flowering seasonality corresponds well with peak activity of their pollinators. However, there is little evidence that the bees are dependent on these fragrance hosts. The orchids tap the majority of euglossine species and individuals for pollinator services during any given season, but most of those bee species that temporarily lack orchid fragrance hosts persist in the area, continually emerge from nests, and seek floral fragrance compounds. Pollinator specificity occurs in less than half of the orchids, and host specificity is rare. Geographic distributions of nearly all orchid-pollinator pairs are not mutually inclusive. Moreover, nearly a third of the local male euglossine bee species censused are not pollinators of any fragrance orchids in the area. Local alternative fragrance sources occur. The orchid-male euglossine bee interaction does not appear to represent a mutually obligatory relationship. The orchids may have exploited a preexisting behavioural phenomenon of the bees, and reciprocal evolutionary responses may not have occurred.     

Floral features,pollination biology and breeding system of Chloraea membranacea Lindl. (Orchidaceae: Chloraeinae)

Background and Aims

The pollination biology of very few Chloraeinae orchids has been studied to date, and most of these studies have focused on breeding systems and fruiting success. Chloraea membranacea Lindl. is one of the few non-Andean species in this group, and the aim of the present contribution is to elucidate the pollination biology, functional floral morphology and breeding system in native populations of this species from Argentina (Buenos Aires) and Brazil (Rio Grande do Sul State).

Methods

Floral features were examined using light microscopy, and scanning and transmission electron microscopy. The breeding system was studied by means of controlled pollinations applied to plants, either bagged in the field or cultivated in a glasshouse. Pollination observations were made on natural populations, and pollinator behaviour was recorded by means of photography and video.

Key Results

Both Argentinean and Brazilian plants were very consistent regarding all studied features. Flowers are nectarless but scented and anatomical analysis indicates that the dark, clavate projections on the adaxial labellar surface are osmophores (scent-producing glands). The plants are self-compatible but pollinator-dependent. The fruit-set obtained through cross-pollination and manual self-pollination was almost identical. The main pollinators are male and female Halictidae bees that withdraw the pollinarium when leaving the flower. Remarkably, the bees tend to visit more than one flower per inflorescence, thus promoting self-pollination (geitonogamy). Fruiting success in Brazilian plants reached 60·78 % in 2010 and 46 % in 2011. Some pollinarium-laden female bees were observed transferring pollen from the carried pollinarium to their hind legs. The use of pollen by pollinators is a rare record for Orchidaceae in general.

Conclusions

Chloraea membrancea is pollinated by deceit. Together, self-compatibility, pollinarium texture, pollinator abundance and behaviour may account for the observed high fruiting success. It is suggested that a reappraisal and re-analysis of important flower features in Chloraeinae orchids is necessary.     

聚叶钗子股-中国兰科新记录种及形态特征增补(英文稿)

报道了产自滇东南的中国兰科植物一新记录种--聚叶钗子股（Luisia appressifolia Averyanov）。研究发现,已往文献报道该种时,对其花部特征（如花颜色、萼片及花瓣形状、大小等）的描述仅依据腊叶标本,因标本严重失水导致描述信息不准或缺失。本文根据新鲜植株和花部材料对该种相关形态特征给予了补充。     

Comparative study of nutritional mode and mycorrhizal fungi in green and albino variants of Goodyera velutina,an orchid mainly utilizing saprotrophic rhizoctonia

The majority of chlorophyllous orchids form mycorrhizal associations with so‐called rhizoctonia fungi, a phylogenetically heterogeneous assemblage of predominantly saprotrophic fungi in Ceratobasidiaceae, Tulasnellaceae, and Serendipitaceae. It is still a matter of debate whether adult orchids mainly associated with rhizoctonia species are partially mycoheterotrophic. Here, we investigated the nutritional modes of green and albino variants of Goodyera velutina, an orchid species considered to be mainly associated with Ceratobasidium spp., by measuring their ¹³C and ¹⁵N abundances, and by molecular barcoding of their mycorrhizal fungi. Molecular analysis revealed that both green and albino variants of G. velutina harbored a similar range of mycobionts, mainly saprotrophic Ceratobasidium spp., Tulasnella spp., and ectomycorrhizal Russula spp. In addition, stable isotope analysis revealed that albino variants were significantly enriched in ¹³C but not so greatly in ¹⁵N, suggesting that saprotrophic Ceratobasidium spp. and Tulasnella spp. are their main carbon source. However, in green variants, ¹³C levels were depleted and those of ¹⁵N were indistinguishable from the co‐occurring autotrophic plants. Therefore, we concluded that the albino G. velutina variants are fully mycoheterotrophic plants whose C derives mainly from saprotrophic rhizoctonia, while the green G. velutina variants are mainly autotrophic plants, at least at our study site, in spite of their additional associations with ectomycorrhizal fungi. This is the first report demonstrating that adult nonphotosynthetic albino variants can obtain their nutrition mainly from nonectomycorrhizal rhizoctonia.     

始兴斑叶兰(兰科)的订正

通过仔细研究藏于中国科学院植物研究所标本馆(PE)以及中国科学院华南植物园标本馆(IBSC)的始兴斑叶兰Goodyera shixingensis K. Y. Lang的模式及等模式标本, 并同作者野外观察和采集的小小斑叶兰G. yangmeishanensis T. P. Lin的新鲜植物和文献描述以及标本进行比较, 证实始兴斑叶兰应为小小斑叶兰的异名。     

Anther cap retention prevents self-pollination by elaterid beetles in the South African orchid Eulophia foliosa

BACKGROUND AND AIMS: Pollination by insects that spend long periods visiting many flowers on a plant may impose a higher risk of facilitated self-pollination. Orchids and asclepiads are particularly at risk as their pollen is packaged as pollinia and so can be deposited on self-stigmas en masse. Many orchids and asclepiads have adaptations to limit self-deposition of pollinia, including gradual reconfiguration of pollinaria following removal. Here an unusual mechanism--anther cap retention--that appears to prevent self-pollination in the South African orchid Eulophia foliosa is examined. METHODS: Visits to inflorescences in the field were observed and pollinators collected. Visitation rates to transplanted inflorescences were compared between a site where putative pollinators were abundant and a site where they were rare. Anther cap retention times were determined for removed pollinaria and atmospheric vapour pressure deficit was recorded concurrently. Anther cap anatomy was examined using light microscopy. KEY RESULTS: Eulophia foliosa is pollinated almost exclusively by Cardiophorus obliquemaculatus (Elateridae) beetles, which remain on the deceptive inflorescences for on average 301 s (n = 18). The anther cap that covers the pollinarium is retained for an average of 512 s (n = 24) after pollinarium removal by beetles. In all populations measured, anther cap dimensions are greater than those of the stigmatic cavity, thus precluding the deposition of self-pollinia until after the anther cap has dropped. An anatomical investigation of this mechanism suggests that differential water loss from regions of the anther cap results in opening of the anther cap flaps. This is supported by observations that as atmospheric vapour pressure deficits increased, the duration of anther cap retention was reduced. CONCLUSIONS: Flowers of E. foliosa are specialized for pollination by elaterid beetles. Retention of anther caps for a period exceeding average visit times by beetles to inflorescences appears to prevent facilitated self-pollination in E. foliosa effectively.     

五唇兰大孢子发生的超微结构观察

五唇兰(Doritis pulcherrima Lind l．)大孢子母细胞在减数分裂前呈长圆形,细胞核偏向珠孔端,细胞呈现极性分化。大孢子母细胞第一次减数分裂形成二分体。随后,二分体珠孔端的一个细胞退化,合点端的一个细胞体积增大成为功能大孢子。功能大孢子进行第二次减数分裂,形成二核胚囊。这一过程属于双孢子葱型胚囊的大孢子发生类型。珠孔端的二分体细胞(大孢子)在退化过程中质膜保持完好,液泡数量增多,染色质高度凝集,具有细胞程序死亡的部分特征。功能大孢子的细胞器和染色质分布均匀。功能大孢子合点端的细胞壁上有发达的胞间连丝,二核胚囊期胞间连丝消失。在功能大孢子靠近合点端一侧有吞噬结构,其内含有结构模糊的细胞器