Deceptive Species Research Articles

COMPARATIVE APPROACHES TO THE EVOLUTION OF REPRODUCTIVE ISOLATION: A COMMENT ON SCOPECE ET AL. 2007

Speciation can be driven by the evolution of many forms of reproductive isolation. Comparative study is a powerful approach for elucidating the relative importance of individual isolating barriers in the speciation process. A recent contribution by Scopece and colleagues provides comparative data for two groups of deceptive pollination orchids and aims to test hypotheses about which forms of isolation are most important in the two clades. The authors compare pollinator isolation and postmating isolation between the two orchid groups, and conclude that food-deceptive orchid species have less isolation by pollinator specificity than sexually deceptive species, and that postmating isolation is more important in the food-deceptive clade. Although we find this approach to be novel and potentially powerful, these conclusions are called into question by the methods used to define and select species and quantify pollinator isolation. Definition and selection of taxa were performed in a biased manner that undermines the ability to infer general patterns of speciation. Furthermore, pollinator isolation was calculated inconsistently for the two groups under study, effectively nullifying the comparison.

Implications of pollination by food and sexual deception for pollinator specificity, fruit set, population genetics and conservation of Caladenia (Orchidaceae)

Caladenia is very unusual in that it contains species that attract pollinators by two different strategies, food and sexual deception. Among the sexually deceptive species, baiting for pollinators has shown that within populations orchid species are typically pollinated by a single species of thynnine wasp. However, some wasp species can be pollinators of more than one species of orchid usually when their ranges do not overlap. There is a trend for closely related orchids to exploit wasps from the same genus, with different lineages of orchids often pollinated by different genera. Very little is known about pollination of food-deceptive Caladenia species, although it is evident they attract a suite of generalist food-seeking insects. Food-deceptive species have a higher pollination rate than do sexually deceptive species. Studies of population genetics and pollen movements are few, although they suggest a pattern of fine-scale genetic structuring within populations, owing to predominantly restricted seed dispersal and low genetic differentiation among populations as a consequence of rare long-distance seed-dispersal events. Both evolutionary and ecological research of Caladenia will greatly benefit from a better understanding of the insect species involved in pollination, their ecological requirements and the ecological and genetic consequences of food and sexual deception.

Demographic variation between populations of Caladenia orientalis - a fire-managed threatened orchid

Caladenia orientalis (G.W.Carr) Hopper & A.P.Br. is a critically endangered orchid. The largest known populations are confined to fire-managed coastal heathland in southern Victoria. Trends in population dynamics at two closely occurring sites were evaluated against time since fire and rainfall, between 2000 and 2008, to provide ecological and biological information relevant to population management. At both sites, decreased plant size was inversely correlated with time since fire and the number of non-reproductive plants was positively correlated with time since fire. Rates of flowering were inversely correlated with time since fire at only one site (Population 2). The vegetation at this site rapidly accumulated after fire, whereas recovery was relatively slow at the other site. Rainfall was not correlated with rates of flowering or leaf width at either of the study sites, although there was a weak inverse relationship between rainfall and the number of non-reproductive plants at one site (Population 1). Rates of pollen transport and fruit set were within reported ranges for deceptive species. Fruiting plants were significantly smaller in the following year, whereas non-reproductive plants remained the same size. The results suggest that there may be costs associated with reproductive effort, and that hand-pollinating plants to boost seed production may lead to decreased plant size in the following year. Annual variation in rates of flowering may be influenced by previous reproductive effort. However, long-term population trends are better explained by competition from dominant shrubs, which become increasingly abundant with a lack of fire. Future management prescriptions should include site-specific fire regimes to maintain an open heathland.

Bees and white spiders: unravelling the pollination syndrome of Caladenia rigida (Orchidaceae)

Orchids of the genus Caladenia have been shown to utilise two quite different pollination strategies, namely species-specific sexual deception of thynnine wasps and a more generalist strategy attracting a larger spectrum of foraging insects. While baiting techniques have enabled the identification of numerous pollinators of sexually deceptive Caladenia, insects that pollinate food-advertising species have received little attention. The present study employed a multidisciplinary approach to better evaluate the pollination syndrome of the white spider orchid, Caladenia rigida R.S.Rogers, a species previously reported to utilise both food and sexual deception. This included the observation and capture of potential pollinators of C. rigida through direct observation, pantraps, Malaise traps and pollinator-baiting experiments, and the use of molecular techniques to identify orchid pollinia isolated from carrier insects. We describe a suite of generalist insects visiting and bearing pollinia from C. rigida. In addition, samples collected from the labellum and column of C. rigida contained sugars at levels comparable to those of a known nectar-producing orchid, Microtis parviflora R.Br. Potential osmophores in the clubs and calli stained positively with neutral red and although this character is often associated with sexual deception, we found no evidence for this secondary pollination syndrome in C. rigida. The present study is the first one to provide a detailed description of the pollinators and pollination syndrome of a non-sexually deceptive species within the genus Caladenia and the first report to provide evidence of nectar production by a species within this genus.

Inadvertent social information in foraging bumblebees: effects of flower distribution and implications for pollination

Pollinators are confronted with spatial heterogeneity in floral resources. Acquiring information about their environment enables pollinators to exploit floral resources optimally, and hence strongly affects their fitness. Despite their evolutionary importance, spatial resource distribution and social information use have never been addressed in a plant–pollinator framework. We experimentally tested the effects of inadvertent social information (ISI) use (without or with an experienced demonstrator) in relation to spatial flower distribution (random or patchy) in foraging Bombus terrestris . We studied naïve bees' associative learning when confronted with rewarding and nonrewarding flowers that differed slightly in colour, reproducing the natural mimicry of deceptive species. Naïve bees were more efficient foragers with than without a demonstrator in the patchy flower distribution, suggesting that they used ISI from conspecifics, probably in the form of social attraction at the patch scale. In the random flower distribution, however, ISI did not improve performance of naïve bees, and could not replace individual sampling. Analyses of nonrewarding intraspecific transitions indicate that the efficiency of naïve bees in deceptive species pollination was lowered when rewarding and nonrewarding inflorescences were patchily distributed and especially when bees relied on ISI. Thus, spatial flower distribution and ISI availability interact in determining pollinator behaviour, which has important consequences for plant community pollination. This suggests that bumblebees are adapted to exploit patchily distributed resources socially, a characteristic that might be exploited by deceptive plant species. By coupling behavioural and community ecology, this study offers promising perspectives for cognitive ecology studies in plant–pollinator interactions.

Should food‐deceptive species flower before or after rewarding species? An experimental test of pollinator visitation behaviour under contrasting phenologies

Many plant species reward their pollinators, whereas some species, particularly among orchids, do not. Similarity of floral cues between co-flowering species influences how rapidly pollinators learn to avoid deceptive plants. This learning process, which affects the reproductive success of deceptive plants, may additionally depend on relative timing of flowering of sympatric rewarding and deceptive species. We tested the combined effects of corolla colour similarity and flowering order of rewarding and deceptive artificial inflorescences on visitation by naïve bumblebees. When deceptive inflorescences were offered after rewarding inflorescences, bumblebees visited them four times more often if both species were similar compared with when they were dissimilar. Pollinator visitation rate to deceptive inflorescences offered before rewarding inflorescences was intermediate and independent of similarity. Thus, early-flowering deceptive species avoid the costs of dissimilarity with rewarding species. This mechanism may favour adaptive evolution of flowering phenology in deceptive species and explain why temperate deceptive orchids usually flower earlier than rewarding ones.

Observations on the effect of nectar-robbery on the reproductive succes of Aeranthes arachnitis (Orchidaceae)

While the presence of nectar is the most common floral reward offered by orchids, approximately one-third of orchid species have evolved mechanisms of deceit whereby the pollinator receives no reward. Lack of reward has been shown to have a significant negative effect on reproductive success in the Orchidaceae, however the phenomenon of nectar-robbery has been poorly studied. Here we investigate the effect of nectar-robbery induced deceit by invasive ants in the nectariferous orchid Aeranthes arachnitis. Fruiting success was found to be below 5% at three sites, including two conservation areas, compared with 48.5% at a site next to plantations. All the populations showed loss of floral nectar, ranging from 64.3% to 100% of flowers observed. Loss of nectar to robbers that do not facilitate pollination not only represents a cost to fruiting success but also a loss of a resource to the orchid through reabsorption of any excess. Using Bell's Theory of nectar concealment it is possible to determine the critical point, below which nectar-robbery negatively affects fruiting success. Based on related angraecoid orchids the proportion of nectar bearing flowers would, theoretically, need to be 70%. The higher levels of reproductive success surrounded by plantations may due to the presence of the non-native Callistemon citrinus acting as nectar source, thus maintaining an increased local abundance of the pollinator. This has important implications for the conservation and management of Aeranthes arachnitis and other species, which rely on nectariferous pollinators, particularly when a nectar bearing species becomes essentially deceptive. The result suggests that management of this nectar-robbery induced deceptive species should involve the manipulation of rewarding species within the surrounding area.

Observations on the effect of nectar-robbery on the reproductive succes of Aeranthes arachnitis (Orchidaceae)

While the presence of nectar is the most common floral reward offered by orchids, approximately one-third of orchid species have evolved mechanisms of deceit whereby the pollinator receives no reward. Lack of reward has been shown to have a significant negative effect on reproductive success in the Orchidaceae, however the phenomenon of nectar-robbery has been poorly studied. Here we investigate the effect of nectar-robbery induced deceit by invasive ants in the nectariferous orchid Aeranthes arachnitis. Fruiting success was found to be below 5% at three sites, including two conservation areas, compared with 48.5% at a site next to plantations. All the populations showed loss of floral nectar, ranging from 64.3% to 100% of flowers observed. Loss of nectar to robbers that do not facilitate pollination not only represents a cost to fruiting success but also a loss of a resource to the orchid through reabsorption of any excess. Using Bell's Theory of nectar concealment it is possible to determine the critical point, below which nectar-robbery negatively affects fruiting success. Based on related angraecoid orchids the proportion of nectar bearing flowers would, theoretically, need to be 70%. The higher levels of reproductive success surrounded by plantations may due to the presence of the non-native Callistemon citrinus acting as nectar source, thus maintaining an increased local abundance of the pollinator. This has important implications for the conservation and management of Aeranthes arachnitis and other species, which rely on nectariferous pollinators, particularly when a nectar bearing species becomes essentially deceptive. The result suggests that management of this nectar-robbery induced deceptive species should involve the manipulation of rewarding species within the surrounding area.

PATTERNS OF REPRODUCTIVE ISOLATION IN MEDITERRANEAN DECEPTIVE ORCHIDS

The evolution of reproductive isolation is of central interest in evolutionary biology. In plants, this is typically achieved by a combination of pre- and postpollination mechanisms that prevent, or limit, the amount of interspecific gene flow. Here, we investigated and compared two ecologically defined groups of Mediterranean orchids that differ in pollination biology and pollinator specificity: sexually deceptive orchids versus food-deceptive orchids. We used experimental crosses to assess the strength of postmating prezygotic, and postzygotic reproductive isolation, and a phylogenetic framework to determine their relative rates of evolution. We found quantitative and qualitative differences between the two groups. Food-deceptive orchids have weak premating isolation but strong postmating isolation, whereas the converse situation characterizes sexually deceptive orchids. Only postzygotic reproductive isolation among food-deceptive orchids was found to evolve in a clock-like manner. Comparison of evolutionary rates, within a common interval of genetic distance, showed that the contribution of postmating barriers was more relevant in the food-deceptive species than in the sexually deceptive species. Asymmetry in prezygotic isolation was found among food-deceptive species. Our results indicate that postmating barriers are most important for reproductive isolation in food-deceptive orchids, whereas premating barriers are most important in sexually deceptive orchids. The different rate of evolution of reproductive isolation and the relative strength of pre- and postmating barriers may have implication for speciation processes in the two orchid groups.

Competition for pollinator visitation between deceptive and rewarding artificial inflorescences: an experimental test of the effects of floral colour similarity and spatial mingling

Summary 1 While many plant species offer rewards (e.g. nectar) to pollinators, some species, particularly in orchids, do not provide rewards. Ecological factors, such as interactions with rewarding co-flowering species may affect pollinator visitation rates to such deceptive species by influencing pollinator ability to learn to avoid deceptive plants (avoidance learning). 2 We tested the effect of flower colour similarity (similar vs dissimilar) and fine-scale spatial mingling (monospecific vs heterospecific patches) of rewarding and deceptive artificial plants on pollinator visitation in a fully crossed design. We also examined the effect of these factors on learning of initially naive bumblebees. 3 Over time, bumblebees increasingly avoided the deceptive plants, but at a significantly faster rate when deceptive and rewarding plants had dissimilar flower colours than when they were similar. 4 Deceptive plants received more visits when mingled in heterospecific patches with rewarding plants of similar flower colour than when mingled with dissimilar ones. This difference was not significant when rewarding and deceptive plants were spatially separated in monospecific patches. 5 In conclusion, both spatial mingling and flower colour similarity affected pollinator visitation to and avoidance learning of deceptive plants. This proves the validity of artificial experimental systems to study the isolated and joint effect of plant traits, and ecological factors that are crucial for the maintenance of deceptive species in natural populations.

Variability in Floral Scent in Rewarding and Deceptive Orchids: The Signature of Pollinator-imposed Selection?

A comparative investigation was made of floral scent variation in the closely related, food-rewarding Anacamptis coriophora and the food-deceptive Anacamptis morio in order to identify patterns of variability of odour compounds in the two species and their role in pollinator attraction/avoidance learning. Scent was collected from plants in natural populations and samples were analysed via quantitative gas chromatography and mass spectrometry. Combined gas chromatography and electroantennographic detection was used to identify compounds that are detected by the pollinators. Experimental reduction of scent variability was performed in the field with plots of A. morio plants supplemented with a uniform amount of anisaldehyde. Both orchid species emitted complex odour bouquets. In A. coriophora the two main benzenoid compounds, hydroquinone dimethyl ether (1,4-dimethoxybenzene) and anisaldehyde (methoxybenzaldehyde), triggered electrophysiological responses in olfactory neurons of honey-bee and bumble-bee workers. The scent of A. morio, however, was too weak to elicit any electrophysiological responses. The overall variation in scent was significantly lower in the rewarding A. coriophora than in the deceptive A. morio, suggesting pollinator avoidance-learning selecting for high variation in the deceptive species. A. morio flowers supplemented with non-variable scent in plot experiments, however, did not show significantly reduced pollination success. Whereas in the rewarding A. coriophora stabilizing selection imposed by floral constancy of the pollinators may reduce scent variability, in the deceptive A. morio the emitted scent seems to be too weak to be detected by pollinators and thus its high variability may result from relaxed selection on this floral trait.

Pollination of the European food-deceptive Traunsteinera globosa (Orchidaceae): the importance of nectar-producing neighbouring plants

European food-deceptive orchids generally flower early in spring and rely on naïve pollinators for their reproduction. Some species however, flower later in the summer, when many other rewarding plants species are also in bloom. In dense flowering communities, deceptive orchids may suffer from competition for pollinator resources, or might alternatively benefit from higher community attractiveness. We investigated the pollination strategy of the deceptive species Traunsteinera globosa, and more specifically whether it benefited from the presence of coflowering rewarding species. We carried out a population survey to quantify the density and reproductive success of the orchid as well as the density of all coflowering species. Our results suggest that the deceptive orchid not only benefited from the presence of coflowering species, but that interestingly the density of the species Trifolium pratense was significantly positively correlated with the orchid's reproductive success. This species might simply act as a magnet species attracting pollinators near T. globosa, or could influence the orchid reproductive fitness through a more species-specific interaction. We propose that morphological or colour similarities between the two species should be investigated in more detail to decipher this pollination facilitation effect.

Effect of floral display on reproductive success in terrestrial orchids

Almost one-third of all species in the familyOrchidaceae offer no reward to insect pollinators. In the absence of a reward, floral display (number of flowers), may be the most important component of insect attraction but the role of floral display in capsule production of both deceptive (nectarless) and rewarding (nectariferous) orchids has not yet been satisfactorily explored. Based on our theoretical considerations, we propose and test here the following hypotheses: (i) deceptive species flower earlier than rewarding ones, (ii) reproductive success in deceptive species is lower than that in rewarding ones, (iii) reproductive success is independent of the number of flowers in the inflorescence in both deceptive and rewarding orchids. Our data supported hypotheses (i) and (ii). In 9 out of our 12 populations of deceptive species and in 10 out of 12 populations of rewarding species we found support for our hypothesis (iii).

Phylogeography of pollinator‐specific sexually deceptiveChiloglottistaxa (Orchidaceae): evidence for sympatric divergence?

Divergence in sexually deceptive orchids is thought to occur through shifts in the attraction of specific pollinators, a process that is mediated by changes in the floral odours that lure sexually excited male insects. We investigated the origin of reproductive isolation in a sexually deceptive species complex of Chiloglottis R.Br. (Orchidaceae: Diurideae). Two geographically separated montane regions in eastern Australia were sampled, each containing sympatric pairs of orchid taxa presently found under the name, Chiloglottis pluricallata. Behavioural tests confirmed at least three distinct orchid taxa that specifically attract different pollinators. An artificial crossing experiment among two taxa from one region demonstrated their interfertility, and confirmed isolation to be a function of pollinator attraction. A phylogeographic analysis using amplified fragment length polymorphisms (AFLPs) indicated that samples from each geographical region are most closely related, a pattern consistent with in situ or sympatric divergence. However, an extensive population genetic study on two taxa from one region failed to entirely reject the possibility of intertaxon gene flow. Although clear genetic differentiation of the taxa is evident in two out of three sites where both grow in direct sympatry, overall, the two taxa are not strongly distinguished by AFLP markers. The reconstruction of a simple bifurcating pattern of divergence may be confounded by a combination of contemporary population-level processes operating within each taxon, the retention of ancestral polymorphism or intertaxon gene flow.

Ants visit nectaries of Epidendrum denticulatum (Orchidaceae) in a Brazilian rainforest: effects on herbivory and pollination.

Epidendrum denticulatum (Orchidaceae) produces nectar on the petioles of buds, flowers, and fruits (extrafloral nectaries) but no nectar is found on its flowers, and it is probably a deceptive species. In the Brazilian Atlantic rainforest, some aspects of both the ecology and behavior of Camponotus sericeiventris (Formicinae) and Ectatomma tuberculatum (Ponerinae), two ant species foraging on E. denticulatum extrafloral nectaries, were investigated. Both experiments, using termites as baits and field observations, suggest that these ant species are able to prevent reproductive organ herbivory, without affecting pollinator behaviour. Since a low fruit set is often cited as a characteristic of the family, especially for deceptive species, ants attracted to orchid inflorescences protect reproductive structures and increase the probability of pollination success. Epidendrum denticulatum flowers were visited and probably pollinated by Heliconius erato (Nymphalidae) and Euphyes leptosema (Hesperiidae).

Pollinator limitaton in a deceptive orchid, Pogonia japonica, on a floating peat mat

Deceptive orchid species that offer no floral rewards to pollinators often experience pollinator limitation because they. The breeding system and fruit set were investigated in order to examine pollinator limitation for a population of a deceptive orchid, Pogonia japonica, on a floating peat mat in Mizorogaike Pond, western Japan. Fruit sets for outcross-pollinated, self-pollinated and pollinator-excluded flowers were 75%, 80%, and 0%, respectively. Thus, this species was self-compatible but neither autogamous nor apogamous. The fruit set for open-pollinated flowers was 22.9% and 17.4% in 1994 and 1995, suggesting that pollinator limitation did occur in the field. Larger flowers were more likely to develop into fruit than smaller ones in open pollination (36%vs 8%). Thus, flower size seems to affect fruiting of this species. No effective visits by major pollinators such as bees, which could carry pollinia, were observed during 16.5 h of observation during daytime. Instead, thrips were often found moving on gynostemium or pollinia and circumstantial evidence that suggests thrips may partly transfer pollen in pieces out of a granular pollinium of P. japonica was obtained. Pogonia japonica should come to use thrips as a pollinator to supplement low fruit set under limited flower visitation by major pollinators.

Inbreeding depression in a rare deceptive orchid

We quantified inbreeding depression for seed maturation and germination in a deceptively pollinated orchid (Dactylorhiza praetermissa (Druce) Soó). Deceptive species do not provide any reward to their pollinators, which thus visit few flowers per plant. Therefore, deceptive species are predicted to experience high outcrossing. In agreement with the prediction that species with high outcrossing rate should possess a heavy genetic load, we demonstrated inbreeding depression in one of the populations we studied. More surprisingly, we found some evidence of inbreeding depression at a small geographic scale. This was not expected, as deceptive orchids generally disperse their pollen and their seeds over long distances. We also demonstrated that the position of a flower within an inflorescence interacts with the type of cross. This indicates that resource availability might modify how severely deleterious mutations affect reproductive success. This could also explain why the intensity of inbreeding depression seems, in the populations we studied, to be determined more by environmental factors than by inbreeding level, as estimated from molecular markers. Inferences in terms of conservation biology are drawn from these results.Key words: inbreeding depression, deceptive pollination, orchid, Dactylorhiza praetermissa.

Pollinator-Induced Density Dependence in Deceptive Species

Many animal-pollinated species experience low visitation rates and, in some cases, stand on the brink of extinction because they are poorly fertilized. Among these plants, some are deceptive species (flowering plants that do not offer any reward to their pollinators). A learning process that pollinators undergo determines visitation rate in those food frauds that do not mimic rewarding models. Pollinators that visit cheating species avoid them after having experienced the absence of reward a few times and then visit rewarding plants. We modeled this learning process, using classical optimal foraging and game theory tools, and applied our model to survey how visitation rate can be adjusted in deceptive species in a density-dependent way and how it can influence the population dynamics of those species. We found pollinator behavior to induce positive density dependence at low density (Allee effect) and therefore to create a threshold density under which population survival is not possible. Moreover, negative density dependence occurs at high density so that in most cases pollination limitation creates a stable demographic equilibrium. Stochastic simulations were performed to investigate the stability of populations at these equilibria and estimate their mean time to extinction. Because some parameters such as pollinator density or habitat fragmentation were explicitly taken into account, we tried to describe environmental conditions conducive to a deceptive plant's survival.

Pollen Carryover, Geitonogamy, and the Evolution of Deceptive Pollination Systems in Orchids

Geitonogamy (transfer of pollen among flowers on the same plant) may lead to reduced outcrossing and interfere with sex function. Orchids with pollen packaged into pollinaria would be expected to be particularly vulnerable to the loss of cross-mating opportunities imposed by geitonogamy. We tested the hypothesis that the absence of floral rewards in many orchid species is a means of reducing geitonogamy. Experiments with the deceptive species Orchis mascula and Orchis morio showed that queen bumble bees probe more flowers and stay longer on plants when artificial nectar is added to the flowers. Overall, the data indicated that the evolution of nectar production in deceptive Orchis species would result in moderate to high levels of geitonogamy, as a consequence of the greater number of flowers probed and longer visit duration (∼60 s) by pollinators. However, the estimated levels of geitonogamy were less than expected, due both to a time delay before freshly withdrawn pollinaria bend into the correct position to strike a stigma and to extensive carryover of pollen. The time elapsed before a freshly withdrawn pollinarium is in the correct position to strike the stigma was found to vary 30–80 s, depending on the orchid species. Since pollinators usually spend <30 s on an inflorescence, we estimate that natural populations of the study species are highly outcrossed. The fraction of the pollen load carried over from flower to flower was found to be 0.67 in O. mascula. Selection should favor longer delays in pollinaria bending and extensive pollen carryover in nectar-producing orchids. This is corroborated by the nectariferous orchid Platanthera chlorantha, which we found to have a pollinaria bending delay of 80 s and a high pollen carryover fraction (0.87). In general, selection for traits that prevent geitonogamy should occur only when pollinators are abundant. Since fruit set of orchids is usually pollinator limited, additional explanations may have to be sought to explain deception. The most plausible complementary hypothesis is that resources in pollinator-limited orchids are invested in advertising display, rather than nectar production.

POLLEN CARRYOVER, GEITONOGAMY, AND THE EVOLUTION OF DECEPTIVE POLLINATION SYSTEMS IN ORCHIDS

Geitonogamy (transfer of pollen among flowers on the same plant) may lead to reduced outcrossing and interfere with sex function. Orchids with pollen packaged into pollinaria would be expected to be particularly vulnerable to the loss of cross-mating opportunities imposed by geitonogamy. We tested the hypothesis that the absence of floral rewards in many orchid species is a means of reducing geitonogamy. Experiments with the deceptive species Orchis mascula and Orchis morio showed that queen bumble bees probe more flowers and stay longer on plants when artificial nectar is added to the flowers. Overall, the data indicated that the evolution of nectar production in deceptive Orchis species would result in moderate to high levels of geitonogamy, as a consequence of the greater number of flowers probed and longer visit duration (∼60 s) by pollinators. However, the estimated levels of geitonogamy were less than expected, due both to a time delay before freshly withdrawn pollinaria bend into the correct position to strike a stigma and to extensive carryover of pollen. The time elapsed before a freshly withdrawn pollinarium is in the correct position to strike the stigma was found to vary 30–80 s, depending on the orchid species. Since pollinators usually spend <30 s on an inflorescence, we estimate that natural populations of the study species are highly outcrossed. The fraction of the pollen load carried over from flower to flower was found to be 0.67 in O. mascula. Selection should favor longer delays in pollinaria bending and extensive pollen carryover in nectar-producing orchids. This is corroborated by the nectariferous orchid Platanthera chlorantha, which we found to have a pollinaria bending delay of 80 s and a high pollen carryover fraction (0.87). In general, selection for traits that prevent geitonogamy should occur only when pollinators are abundant. Since fruit set of orchids is usually pollinator limited, additional explanations may have to be sought to explain deception. The most plausible complementary hypothesis is that resources in pollinator-limited orchids are invested in advertising display, rather than nectar production.