Jiang-Yun Gao

Pollination - Flexible style that encourages outcrossing

Despite the convenience of self-pollination (selfing) in flowering plants , the detrimental effects of inbreeding that follow repeated selfing have promoted strong natural selection for mating systems that ensure successful cross-fertilization (outcrossing). Here we describe a mechanism deployed by some tropical ginger flowers to avoid self-pollination — the flower moves its stigma (style), which normally acts as the pollen receptor, out of the way while its anther is releasing pollen. This cunning evasion adds to the diversity of pollination strategies that have contributed to the evolutionary success of flowering plants.

Mating system and stigmatic behaviour during flowering of Alpinia kwangsiensis (Zingiberaceae)

Abstract. Little is known about the breeding systems of tropical perennial ginger species. In this paper, we provide information about the breeding system of Alpinia kwangsiensis in Yunnan, Southwest China, specifically self-compatibility, mechanisms promoting outcrossing, and the visitation characteristics of pollinators. Populations of A. kwangsiensis have two specific phenotypes that differ in flowering behaviour: 1) “cataflexistyle” individuals in which the stigma is held erect above the dehiscent anther when anthesis begins in the morning and becomes decurved under the anther at noon and 2) “anaflexistyle” individuals in which the receptive stigma is decurved under the indehiscent anther first and moves into a reflexed superior position above the anther as it begins to shed pollen at mid-day. The stigmatic movements in the two floral phenotypes, which occur in a ratio of 1:1 in natural populations, are synchronous and correlate with the foraging behaviour of floral visitors; pollination is effected only between floral forms. Field experiments indicate that A.kwangsiensis is self-compatible and dependent upon insects for fertilization. This newly reported floral mechanism, which we have named “flexistyly,” adds to the repertoire of devices that have evolved in flowering plants to insure outcrossing.

Reproductive biology of Alpinia blepharocalyx (Zingiberaceae): another example of flexistyly

The floral biology and breeding system of Alpinia blepharocalyx were studied in Yunnan province, southwest China. Our results indicate that populations of A. blepharocalyx have two floral morphs, which differ in flowering behaviour: the cataflexistylous morph in which the stigma is held erect above the dehiscent anther when anthesis begins in the morning and becomes curved under the anther at afternoon, and the anaflexistylous morph in which the receptive stigma is curved under the indehiscent anther first and moves into a reflexed superior position above the anther as it begins to shed pollen in the afternoon; the flowering period of both floral morphs is 12 hours; the stylar movements in the two floral morphs are synchronous, and they have similar traits to those found in other Alpinia species previously reported. Also, on average, cataflexistylous flowers are larger than anaflexistylous flowers, especially the labellum and corolla tube length; moreover, the P/O ratio of the two floral morphs is significantly different: the cataflexistylous morph has more pollen grains and fewer ovules than the anaflexistylous morph; the evolutionary significance of this comparison is discussed. Cataflexistylous flowers were observed to produce a lower concentration of nectar than that of anaflexistylous flowers before 11:00 a.m., but they then have higher nectar concentration; cataflexistylous flowers always have more nectar than anaflexistylous flowers. Flowers of A. blepharocalyx were visited by fewer insects at a lower frequency, including honey bees (Apis cerana cerana) and two species of carpenter bees (Xylocopa spp.). No significant differences were found in the fruit set among the hand-pollination treatments regardless of selfing (geitonogamy and autogamy) or crossing (intermorph and intramorph); but all hand-pollination treatments exhibited much higher fruit set than the controls; meanwhile, no fruit set occurred in the unpollinated bagged plants. Pollen tube growth was examined using fluorescence microscopy following self, intramorph, and intermorph hand pollinations at different times of the day; the pollen tubes of both floral morphs have the same growth rate and the capability to reach the ovary. Both the results of pollen tube growth and fruit sets under different pollination conditions show that A. blepharocalyx is self-compatible and dependent upon insects for pollination. The distinctive flexistyly mechanism of A. blepharocalyx is likely a floral mechanism that promotes effective intermorph pollen transfer.

Reproductive biology of two Himalayan alpine gingers (Roscoea spp., Zingiberaceae) in China: pollination syndrome and compensatory floral mechanisms

According to the concept of pollination syndromes, floral traits reflect specialisation to a particular pollinator or set of pollinators. However, the reproductive biology of endemic, and often specialised, plants may require increased attention as climate change accelerates worldwide. Species of Roscoea endemic to the Himalayan region have striking orchid-like flowers with long corolla tubes, suggesting pollination by long-tongued insects. Until now, the reproductive biology of species of Roscoea has been poorly documented. We investigated the floral biology, breeding system and pollination ecology of R. cautleoides and R. humeana, from Hengduan Mountains, a global biodiversity hotspot in southwest China. We also tested whether floral longevity increases pollination success. Pollination experiments showed that the two species were self-compatible and depended on insects for fruit production. Over several flowering seasons we did not observe any potential pollinators with long tongues that matched the corolla tube visiting flowers in centres of distribution. The principal pollinators observed were pollen-collecting generalist bees, with low visitation frequencies. In general, members of the ginger family are characterised by short-lived (usually 1 day) flowers, but flowers of R. cautleoides and R. humeana last 8 and 6 days, respectively. Removing stigmas decreased fruit set in both study populations. Our results suggest that the original pollinators may have been long-tongued insects that are now absent from the Chinese Himalayas because habitats have responded to climate change. However, long-lived and self-compatible flowers, coupled with the presence of generalist pollinators, are traits that have allowed these gingers to reproduce and continue to persist in the alpine habitats.

Rain pollination provides reproductive assurance in a deceptive orchid

BACKGROUND AND AIMS Abiotic pollination by wind or water is well established in flowering plants. In some species pollination by rain splashes, a condition known as ombrophily, has been proposed as a floral strategy. However, evidence for this type of abiotic pollination has remained controversial and many reported cases have subsequently been shown to be false. This study investigates ombrophily in the deceptive orchid Acampe rigida to determine the mechanism by which this species is able to maintain high fecundity, despite flowering during the rainy season in south-west China when pollinators are scarce. METHODS The floral mechanisms promoting rain pollination in A. rigida were observed and described in detail. Controlled pollination experiments and observations of floral visitors were conducted. A field experiment using rain shelters at 14 sites in Guangxi, south-west China, evaluated the contribution of rain pollination to fruit-set. KEY RESULTS During rainfall, raindrops physically flicked away the anther cap exposing the pollinarium. Raindrops then caused pollinia to be ejected upwards with the strap-like stipe pulling them back and causing them to fall into the stigmatic cavity, resulting in self-pollination. Neither flower nor pollen function were damaged by water. Although A. rigida is self-compatible, it is incapable of autonomous self-pollination without the assistance of rain splashes. The results of the rain-sheltering experiment indicated that rain pollination contributed substantially to increasing fruit-set, although there was variation among sites in the intensity of this effect. CONCLUSIONS A. rigida flowers during the rainy season, when pollinators are scarce, and ombrophily functions to provide reproductive assurance without compromising opportunities for outcrossing.

Autonomous self-pollination and insect visitation in a saprophytic orchid, Epipogium roseum (D.Don) Lindl.

Reproductive biology of saprophytic plants has been poorly studied. Epipogium roseum (D.Don) Lindl. is a small saprophytic orchid that is widely distributed in tropical and subtropical Asia, Australia and Africa. The floral biology and insect visitation of E. roseum were studied in Xishuangbanna, south Yunnan Province, China. E. roseum possesses an obligate self-pollination system, in which the degenerative rostellum has lost its function as a physical barrier separating the stigma and stamens (pollinia), allowing contact between the stigmatic secretions and the pollinia during bud development. Flowers of E. roseum usually open and successfully attract insect visitors. The Asian honey bee (Apis cerana cerana) was the only visitor observed, and regularly visited flowers of E. roseum for nectar. However, these bees did not carry pollinia away after visiting the flowers due to the absence of a viscid disk in E. roseum; the results of experiments also indicated that the Asian honey bee does not contribute to fruit set in E. roseum. The visiting frequency of Asian honey bees to flowers of E. roseum varied both spatially and temporally. E. roseum does not undergo outcrossing mediated by insects and is adapted to obligate self-pollination. We suggest that this may have evolved because of the uncertainty of pollinator services associated with its saprophytic lifestyle. Our current studies do not support the hypothesis that obligate autogamy is favoured by myco-heterotrophic plants due to resource limitations.

The floral biology of Curcumorpha longiflora (Zingiberaceae): A ginger with two-day flowers

Curcumorpha longiflora is a perennial chasmophyte (rock fissure plant) ginger that usually grows in crevices of calcareous rocks and forms patches on the understory of limestone monsoon rainforests. The pollination ecology of C. longiflora was studied by monitoring phenology and flowering behavior, observing pollinator activity (frequency and behavior of visitors), and the quantity and quality of pollination services. We also investigated the germination of pollen grains and growth of pollen tubes after different pollination treatments to detect its breeding system. Based on the results: (1) for the first time in Zingiberaceae a new protandrous mechanism was found with a two-day flowering to avoid autogamy in this species; (2) under field conditions, all individuals of C. longiflora usually produced only one flower every other day to keep geitonogamy to a minimum; (3) germination of pollen grains and growth rates of pollen tubes under different pollination treatments were the same 4 h later after pollination, suggesting that C. longiflora is completely self-compatible; (4) among the limited visitors, Bombus sp. and Apis florae were effective pollinators, but they were active at different times and at different stages of the flower, probably receiving different rewards.

The comparative reproductive biology of a tetraploid species, Hedychium villosum, and its diploid progenitor H. tenuiflorum (Zingiberaceae).

The evolutionary advantages of polyploidy may result from a number of changes in floral traits and breeding system, which may enable polyploids to exploit new habitats and become widespread. In this study, we comparatively investigated the floral biology of the tetraploid species Hedychium villosum and its diploid progenitor H. tenuiflorum, to assess reproductive divergence between the two species. The results showed that flowers of the tetraploid species last longer and produce more nectar than did diploid species. The flowering times of the two species did not overlap at all. Observations of floral visitors in natural populations demonstrated that butterflies and hawkmoths were effective pollinators of both species, but there was a significant difference in butterfly and hawkmoth assemblages between the two species. The hand-pollination experiments and pollen tube growth experiments suggested that diploid H. tenuiflorum was self-incompatible, while tetraploid H. villosum was completely self-compatible. H. villosum has a much wider distribution range and occupies more diverse habitats than H. tenuiflorum. Polyploidisation may enable tetraploid H. villosum to exploit new habitats previously unavailable to diploid H. tenuiflorum.

Morphology, distribution, and chromosome counts of two varieties of Hedychium villosum (Zingiberaceae

Abstract  Polyploidy is a major mechanism of adaptation and speciation in plants. Two varieties of Hedychium villosum, var. villosum and var. tenuiflorum, primarily differ in plant and flower size. Chromosome number suggests that var. tenuiflorum is diploid (2n= 34) and var. villosum is tetraploid (2n= 68). Although the flowers of the two varieties do not have any difference in floral shape, each can be easily distinguished morphologically because the shoots, leaves, and flowers of the tetraploid var. villosum are consistently larger than the diploid var. tenuiflorum. The two varieties each possess distinct geographic ranges and habitats, and no sympatric distribution has been found. The tetraploid var. villosum has a broader geographic distribution range and more diverse ecological habitats than the diploid var. tenuiflorum. The two varieties are also completely reproductively isolated due to the non‐overlap of their flowering times. The two varieties should be recognized as two distinct species as they fulfill the requirements of various species concepts. Thus, we suggested that the tetraploid var. villosum should be kept as Hedychium villosum and the diploid var. tenuiflorum should be renewed to Hedychium tenuiflorum.

Microsatellite markers for Duperrea pavettifolia (Rubiaceae)

PREMISE OF THE STUDY The development of microsatellite primers for Duperrea pavettifolia will be the foundation for mating system analysis and conservation research. METHODS AND RESULTS Nineteen microsatellite markers were developed and characterized in two wild populations by using the Fast Isolation by AFLP of Sequences COntaining repeats (FIASCO) protocol. Polymorphisms were evaluated in 24 individuals from two natural populations. Eleven of these primers generated polymorphic loci. CONCLUSIONS These microsatellite markers will be useful in future investigations into the population genetics and mating system of D. pavettifolia.