The effect of different chiral morphs on visitation rates and fruit set in the orchid Spiranthes spiralis

Background: The arrangement of flowers on inflorescences is important for determining the movement of pollinators within the inflorescence and, consequently, the overall mating success and fruit set of a plant.

Aims: Spiranthes spiralis is an orchid that has a spiralled inflorescence. The species has two chiral forms that show opposite coiling directions (clockwise and anti-clockwise). We tested if this arrangement of inflorescence influences pollinator attraction and behaviour.

Methods: We surveyed two natural populations, analysed the reproductive compatibility of the two morphs and estimated pollination success in natural and experimental populations.

Results: We found that the two morphs were not isolated by pre- or post-mating barriers, occurred with a similar proportion in natural populations and showed similar levels of pollination success both in natural and artificial populations. However, we found a different pattern of pollination success along the inflorescences. In the two morphs, lower flowers experienced a higher pollination rate and this rate decreased along the inflorescence faster in anti-clockwise than in clockwise individuals.

Conclusions: This finding suggests that pollinators visit the flowers sequentially from the lower part of the inflorescences and leave the anti-clockwise individuals more rapidly than the clockwise ones. However, this pollinator behaviour is not detrimental for the pollination success of either of the two morphs.     

Large population sizes mitigate negative effects of variable weather conditions on fruit set in two spring woodland orchids

Global circulation models predict increased climatic variability, which could increase variability in demographic rates and affect long-term population viability. In animal-pollinated species, pollination services, and thus fruit and seed set, may be highly variable among years and sites, and depend on both local environmental conditions and climatic variables. Orchid species may be particularly vulnerable to disruption of their pollination services, as most species depend on pollinators for successful fruit set and because seed germination and seedling recruitment are to some extent dependent on the amount of fruits and seeds produced. Better insights into the factors determining fruit and seed set are therefore indispensable for a better understanding of population dynamics and viability of orchid populations under changing climatic conditions. However, very few studies have investigated spatio-temporal variation in fruit set in orchids. Here, we quantified fruit production in eight populations of the orchid Orchis purpurea that does not reward pollinators and 13 populations of the rewarding Neottia (Listera) ovata during five consecutive years (2002–2006). Fruit production in large populations showed much higher stability than that in small populations and was less affected by extreme weather conditions. Our results highlight the potential vulnerability of small orchid populations to an increasingly variable climate through highly unpredictable fruit-set patterns.     

Pollination biology and reproductive success in four Brazilian species of Gomesa (Orchidaceae: Oncidiinae): Specific pollinators,but high pollen loss and low fruit set

Four species of Gomesa (Gomesa flexuosa, Gomesa ranifera, Gomesa cornigera, and Gomesa riograndensis), a horticulturally important, albeit scarcely studied orchid genus, were investigated. Pollination biology was studied through fieldwork in Rio Grande do Sul in Southern Brazil during two flowering seasons. Breeding systems were studied through controlled pollinations in cultivated plants. All studied species secrete floral oils through elaiophores and are exclusively pollinated by native, oil-collecting bees of the Centridini or Tapinotaspidini tribes. Pollinarium reconfiguration after withdrawal, a feature likely promoting cross-pollination, was recorded in G. cornigera and G. riograndensis. All studied species are pollinator-dependent and either predominantly or fully self-incompatible, that is, unable to set fruit following self-pollination. The used indexes of pollination efficiency consistently scored values below 1, indicating that in all studied species less than one flower is pollinated per pollinarium removed. Accordingly, pollen loss was high, ranging from 40% to 75%. Furthermore, inflorescences in natural populations displayed low fruit sets (below 13%). Gomesa flexuosa presented the highest values of pollinarium removal (36.24%) and deposition (15.34%). Significantly, this is the only studied species bearing a tabula infraestigmatica, a column swelling that bees hold to stabilize themselves while gathering the floral oils. Since pollinators were observed in all studied species spending considerable time (up to 3 min 46 s) and visiting several (up to 19) flowers, we propose that the observed low fruit set is the result of a combination of self-incompatibility, pollinator-mediated self-pollination, and pollen loss.     

Evolution of mutualism in plant-pollinator interactions on islands

The evolution and ecology of interactions between plants and pollinators are discussed based on the studies on the Izu Islands and mainland Honshu, Japan. The species assemblage is depauperate, and long-tongued pollinators are absent or rare on the islands. Bumblebees, one of the most important pollinators in Japan, are generally absent. Plants depending strongly on bumblebee pollination are absent on Izu Islands, but those depending on varied pollinators including bumblebees display smaller flower sizes and accommodate smaller pollinators than their mainland counterparts. Breeding systems of these species also shift to partial inbreeding, possibly an evolutionary result of the decrease in pollinator availability. Changes in flowering phenology between mainland and island populations also occur. Plants in the islands tend to reproduce vegetatively less frequently and produce greater numbers of smaller seeds than those in the mainland. The possibility of evolution on the side of island pollinator species is also discussed, although there are few data on this topic.     

Experimental Studies on Male and Female Reproductive Success: Effects of Variation in Spur Length and Pollinator Activity on Platanthera mandarinorum ssp. hachijoensis (Orchidaceae)

Abstract Field experiments on an orchid, Platanthera mandarinorum ssp. hachijoensis , were carried out to investigate the effects of variations in spur (nectary) length and pollinator activity on reproductive success (RS) of individual plants. Experiments comprised two kinds of treatments: spur shortening and bagging to restrict pollinator activity. Plants with a natural spur lengths range show nearly equal RS, whereas plants with shortened spurs had decreased RS proportional to spur length reduction. Pollinaria attachment (a measure of male RS) to the pollinators seems to demand stricter morphological correspondence than pollen receipt (female RS). Decrease of male and female RSs in spur-treatments was smaller in the case of high pollinator activity than low pollinator activity. Results of the bagging experiments indicated that female RS was greater than male RS in cases of high pollen carryover. These facts suggest that (1) fecundity selection operates more intensely on both male and female functions in the case of low pollinator activity and more intensely on the male function in the case of high pollen carryover, and (2) individuals with different spur lengths in natural populations have nearly equal probabilities of RS after excluding the extreme variants through the reduction of male RS.     

The pollination of Habenaria rhodocheila (Orchidaceae) in South China: When butterflies take sides

Habenaria is one of the largest terrestrial genera in the family Orchidaceae. Most field studies on Habenaria species with greenish–white and nocturnal scented flowers are pollinated by nocturnal hawkmoths and settling moths. However, H. rhodocheila presents reddish flowers lacking a detectable scent and fails to fit the moth pollination syndrome. We investigated the pollinators, breeding system, and functional traits of H. rhodocheila in South China and found that two diurnal swallowtail butterflies Papilio helenus and Papilio nephelus (Papilionidae) were the effective pollinators. When butterflies foraged for nectar in the spur, the pollinia became attached between the palpi. A triangular projected median rostellar lobe was found at the entrance (sinus) of the spur of H. rhodocheila. This lobe divided the spur opening into two entrances forcing butterflies to enter their proboscides through the left or right side. When the projection of median rostellar lobe was removed, the site of pollinium attachment changed to the eyes of the butterflies, leading to a higher rate of pollinium removal but lower rate of pollinium deposition. Our quartz glass cylinder choice experiment suggested that visual rather than olfactory cues provided the major stimuli for butterflies to locate these flowers. Hand pollination experiments suggested this species was self‐compatible but pollinator‐dependent. However, the proportion of seeds with large embryos produced in self‐pollinated fruits was significantly lower than in cross‐pollinated fruits, indicating a significant inbreeding depression. Unlike many other orchid species, fruit set was higher than rates of pollinium removal, indicating a high level of pollination efficiency in a species with friable pollinia. Shifts from moth to butterfly pollination in the genus Habenaria parallel other orchid lineages providing insights into the potential for pollinator‐mediated floral trait selection.     

Effect of bacteria on nutritional status and reproductive success of the Mediterranean fruit fly Ceratitis capitata

Abstract.  Mediterranean fruit flies ( Ceratitis capitata Wiedemann, Diptera: Tephritidae) harbor a community of diazotrophic bacteria in their digestive system. The present study aims to test the hypothesis that bacteria contribute to fly fitness by enhancing copulatory success and egg production in males and females, respectively. After eclosion, flies were fed a full diet containing peptides, sugar and minerals, or a sugar diet, lacking peptides. Subgroups from each diet were fed a mixture of the antibiotics ciprofloxacin and piperacillin. The presence of bacteria, food consumption, weight gain, lipid and protein levels, oviposition in females and copulatory success of males were quantified in the four groups. The antibiotic treatment effectively cleared the gut of bacteria. The relative amounts of food consumed (with or without antibiotics) are similar in all groups. The antibiotics do not inhibit feeding, and their ingestion does not affect dry weight or the amount of protein stored, yet females feeding on the full diet without antibiotics have increased lipid levels. Females fed the full diet produce significantly more eggs than females on the sugar diet, but the presence of bacteria does not affect numbers of eggs produced. However, in the absence of bacteria, the oviposition rate of nutritionally stressed females is significantly accelerated. The presence of bacteria in sugar fed males does not provide them with a mating advantage. Conversely, in males fed a full diet, the presence of bacteria is associated significantly with a shorter latency to mate. It is concluded that, because the bacterial community is present at all stages of the fly's life cycle, at least some species are effectively transmitted from parents to offspring, and removal of bacteria affects measurable physiological and behavioural parameters related to fitness, the association between bacteria and the medfly is mutualistic.     

Plant reproductive susceptibility to habitat fragmentation: review and synthesis through a meta-analysis

The loss and fragmentation of natural habitats by human activities are pervasive phenomena in terrestrial ecosystems across the Earth and the main driving forces behind current biodiversity loss. Animal-mediated pollination is a key process for the sexual reproduction of most extant flowering plants, and the one most consistently studied in the context of habitat fragmentation. By means of a meta-analysis we quantitatively reviewed the results from independent fragmentation studies throughout the last two decades, with the aim of testing whether pollination and reproduction of plant species may be differentially susceptible to habitat fragmentation depending on certain reproductive traits that typify the relationship with and the degree of dependence on their pollinators. We found an overall large and negative effect of fragmentation on pollination and on plant reproduction. The compatibility system of plants, which reflects the degree of dependence on pollinator mutualism, was the only reproductive trait that explained the differences among the species' effect sizes. Furthermore, a highly significant correlation between the effect sizes of fragmentation on pollination and reproductive success suggests that the most proximate cause of reproductive impairment in fragmented habitats may be pollination limitation. We discuss the conservation implications of these findings and give some suggestions for future research into this area.     

Novel interactions of non-pollinating ants with pollinators and fruit consumers in a tropical forest

The tropical ants Ectatomma ruidum and E. tuberculatum (Formicidae) regularly patrol leaves, flowers, and fruits of the understory shrub, Psychotria limonensis (Rubiaceae), on Barro Colorado Island, Panama. Ant and pollinator exclusion experiments elucidated both positive and negative effects of ant attendance on plant reproductive success, including pollination, fruit set, fruit loss, and fruit removal. Ants did not pollinate flowers but did contribute to higher pollination success, probably by increasing the relocation frequency of winged pollinators and thus the rate of flower visitation. Ants also prevented fruit loss to herbivorous insects which were common during the early stages of fruit development. Thus, ant attendance strongly improved both pollination and fruit set whereby plants with ants set more fruit per flower and also lost fewer fruits during fruit maturation. In contrast, ants had a negative effect on the removal of ripe fruits by avian frugivores. Thus, ant attendance has a non-trivial influence on plant reproduction, this interaction being beneficial at some stages of the plant reproductive cycle and carrying costs at another stage. A tight ecological or co-evolved relationship between these Ectatomma spp. and P. limonensis is unlikely given that ant attendance of plants is detrimental to fruit removal. Received: 18 May 1998 / Accepted: 1 March 1999     

Mean corpuscular volume (MCV) as a measure of condition in birds

Haematological parameters, particularly haematocrit, are frequently used in assessing condition in birds. Mean corpuscular volume (MCV) overcomes some of the drawbacks associated with measuring haematocrits and therefore should be a better condition index. We investigated the relationship between these blood parameters and the breeding performances of great skuas Catharacta skua . As predicted from activity budgets of the sexes, male MCVs were significantly positively correlated with hatch date and the MCVs of both sexes were negatively correlated with the number of chicks fledged. No correlations existed between these breeding parameters and haematocrit. Since males provision females and chicks, they probably influence breeding performance via foraging abilities, whereas in females nutritional investment may be more important. This is the first study of a free-living/nondomesticated vertebrate population in which these kinds of relationship have been demonstrated and we conclude that MCV is a useful measure of condition.     

Influence of pollination systems on fruit set and fruit quality in kiwifruit (Actinidia deliciosa)

Kiwifruit (Actinidia deliciosa (Chev.) Liang and Ferguson) is a dioecious species highly pollination dependent, since fruit size is directly correlated with seed number. To evaluate the best pollination system for this species a study of two natural and two artificial pollination systems was carried out and their effect on fruit set and fruit quality was determined. While anemophilous pollination produced few and small fruits, that were not commercially acceptable, high fruit set percentages and good quality fruits were obtained when insects participated in the pollination process. Artificial pollination, performed as hand pollination, improved yield quantity and quality. When environmental conditions impair insect activity this method can be an useful agricultural practice in order to assure a good yield.     

Foraging behaviour of bird pollinators on Embothrium coccineum (Proteaceae) trees in forest fragments and pastures in southern Chile

Abstract We investigated the effects of forest patch size on the behaviour of birds feeding on the flower nectar of the proteaceous tree Embothrium coccineum J. R. et G. Forster, which is typically restricted to forest edges in agricultural landscapes in southern Chile. We quantified reproductive parameters of trees (no. inflorescences per branch, total and open flowers per inflorescence) in forest fragments varying from 1 ha (small), to 20 ha (medium) and to >150 ha (large), and in remnant trees in pastures. Visits to flowers by nectar‐feeding birds were recorded during 30‐min observation periods, spread throughout the day during two flowering seasons, November 1992 and 1993 (n = 242 periods overall). Aggressive encounters among flower visitors were recorded in 1992. We expected less visits to trees in pastures and small forest patches because abundances of Embothrium's main pollinators, the flycatcher Elaenia albiceps and the hummingbird Sephanoides sephaniodes, decreased in smaller patches. We found, however, that pollinator visiting rates were negatively correlated with forest patch area and were highest for pasture trees. This trend was largely due a decline in the number of visits by E. albiceps, the main flower visitor, in larger patches. Hummingbird visits did not change with forest patch size. Lower visitation rates to flowering trees in larger forest fragments seemed to be a consequence of territorial defence by E. albiceps and were unrelated to differences in floral display.     

歪叶榕非传粉小蜂的繁殖策略及其对榕-蜂共生系统的影响

2004年8月至2005年8月在西双版纳热带植物园内,通过广泛收集歪叶榕榕小蜂标本、非传粉小蜂产卵行为学观察和阻止传粉者入果等实验方法,研究了我国西双版纳热带雨林下的一种榕树——歪叶榕Ficus cyrtophylla的榕小蜂群落组成结构、非传粉小蜂的繁殖策略以及它们对榕-蜂共生系统的影响。结果表明,歪叶榕中除了具有唯一传粉榕小蜂Blastophag sp.以外,还具有3种非传粉小蜂Platyneura sp.、Philotrypesis sp.和Sycoscapter sp.。在歪叶榕榕小蜂群落中,传粉榕小蜂占整个群落总数的92.21%,是群落的最主要组成者;主要的非传粉小蜂是Sycoscaptersp.,占5.78%; 其次是Philotrypesissp.,占1.84%,而Platyneurasp.仅占群落总数的0.17%。歪叶榕中的非传粉小蜂通过各自产卵时间和食性分化的策略来利用榕果中的资源繁殖后代。非传粉小蜂寄生使传粉榕小蜂的总数和其雌蜂数量都显著地降低,但是对传粉小蜂雄蜂数量没有显著影响,从而导致传粉榕小蜂的雄性性比显著地增加。这说明非传粉小蜂在选择寄居宿主时具有明显的倾向性,而且更多地将卵产于含有雌性传粉小蜂的瘿花之中。因此,非传粉小蜂通过减少雌性传粉小蜂的数量而降低了榕树的雄性适合度,从而在一定程度上对榕 蜂共生系统的稳定存在和发展产生了负面影响。     

Floral biology,breeding system and pollination ecology of Justicia betonica L. (Acanthaceae): An assessment of its low reproductive success in West Bengal,India

Besides its importance as an ornamental plant, Justicia betonica L. is also used as a medicinal plant for the treatment of several human disorders. However, the population size and abundance of the plant species are very low in Indian states, including West Bengal. The breeding system and pollination ecology of J. betonica are still unclear. Therefore, some reproductive aspects were investigated in order to provide important information for the sustainability of the species. The flowering duration spanned from December to May, with its peak in February–March. Flower opening time was much earlier (5.00–8.00 a.m.) on a hot day (in April–May) than on a cold day (10.00 a.m.–12.00 p.m. in December–January). The time of anther dehiscence coincided with the flower opening time; however, the stigma became receptive later. The plant species is self-compatible but dependent on pollinators for fruit and seed sets. Members of different insect groups like ants, bees, butterflies, flies, moths and wasps visit the flowers. Among them, Allorhynchium metallicum and Halictus acrocephalus are the primary pollinators (based on the “relative pollinator service”). The plant species showed a significant pollination deficit (coefficient of pollination deficit [D] = 0.32) in the open condition. Larvae of the florivorous moth Gatesclarkeana erotias significantly reduced reproductive success by eating their floral parts, ovules and immature seeds. In conclusion, combining the pollination deficit and the feeding activity of phytophagous insects (moth larvae) may reduce the reproductive fitness of J. betonica in the study regions.     

The effect of enemy-release and climate conditions on invasive birds: a regional test using the rose-ringed parakeet (Psittacula krameri) as a case study

Aim Some invasive species succeed particularly well and manage to establish populations across a wide variety of regions and climatic conditions. Understanding how biotic and environmental factors facilitate their invasion success remains a challenge. Here, we assess the role of two major hypotheses explaining invasion success: (1) enemy‐release, which argues that invasive species are freed from their native predators and parasites in the new areas; and (2) climate‐matching, which argues that the climatic similarity between the exotic and native range determines the success of invasive populations. Location India, Israel and the UK. Methods We studied the reproductive success of one of the most successful avian invaders, the rose‐ringed parakeet (Psittacula krameri), in its native range (India) and in two introduced regions, varying in their climate conditions (Israel and the UK). We combined literature and field data to evaluate the role of predation pressure and climatic conditions in explaining the differences in reproductive success between the three regions. Results We found significant differences in reproductive success between regions. In accordance with the enemy‐release hypothesis, we discovered that while predation was the main factor responsible for the reduction of fecundity in India, it did not significantly affect the fecundities of parakeet populations in the two introduced regions. In accordance with the climate‐matching hypothesis, we found that in the colder temperate UK, egg infertility was high, resulting in lower fecundities. Populations in both the warmer Mediterranean climate of Israel and in the native Indian range had significantly lower egg infertility and higher fecundities than the UK populations. Main conclusions Our findings support both the enemy‐release and the climate‐matching hypotheses. While release from predators facilitates the reproductive success and therefore the invasiveness of parakeets in both the UK and in Israel, colder climate impedes reproduction and therefore the spread of parakeets in the UK.     

菜粉蝶对两种迁地保护的兰科植物传粉和繁殖成功的作用

迁地保护是防止物种灭绝的有效措施。为了解在新栖息地兰科植物与昆虫之间的关系, 从而为兰科植物的保护提供借鉴, 作者对迁地栽培于深圳市全国兰科植物种质资源保护中心的本地种血叶兰(Ludisia discolor)和外来种银带虾脊兰(Calanthe argenteo-striata)的传粉系统和繁殖策略进行了观察和研究。血叶兰和银带虾脊兰都具有白色小花组成的花序, 且花有距。在开放栽培条件下, 菜粉蝶(Pieris rapae)是这两种兰科植物唯一有效的传粉者。菜粉蝶携带血叶兰和银带虾脊兰花粉块的部位分别是降落时平衡身体的左侧足部和取食花蜜的喙。两种兰科植物传粉效率较高, 花粉移走与沉降的比值分别为1.14 : 1和0.74 : 1。血叶兰的结实率在2007和2008两年间无显著差异, 且均高于银带虾脊兰。究其原因, 一方面是由于它为传粉者提供报酬; 另一方面是因为血叶兰的花期与菜粉蝶的盛发期相吻合, 有利于充分利用传粉者; 而银带虾脊兰的花期滞后于菜粉蝶的盛发期, 传粉者缺失使得部分花未能授粉。血叶兰和银带虾脊兰都是高度自交亲和的物种, 但不存在无融合生殖和自动自花授粉的现象; 自交和异交的繁殖成功率无显著差异。这两种兰科植物可能存在由传粉者导致的自交现象。血叶兰和银带虾脊兰在迁地栽培到兰科中心后生长良好, 每年花期都有自然结果的现象, 植株周围有新生幼苗的建立, 种群有逐渐扩大的趋势, 显示出迁地保护的可行性。可以预测若干年后, 这两个种在兰科中心具有建立稳定种群的可能性。