Ant Pollination Research Articles

Ant‐Pollination: Conditional Outcomes Depending on Environmental Features and Species Interactions

ABSTRACTThe intricate web of interactions in nature has led to unexpected partnerships between plants and animals, greatly influencing ecosystem dynamics. In this discussion, we'll explore the Pollination Syndrome Hypothesis and consider a scenario where a partnership with unexpected pollinators emerges. We suggest that ant pollination has been largely overlooked, but ants can surprisingly play a crucial role and have a history of success in pollinating dry system plants. We will present both negative and positive aspects that must be observed in ant‐pollination syndrome. Additionally, we aim to explore the often‐underestimated phenomenon of ant pollination and the overlooked tiny, discreet, unnoticed flowers found in our fields and forests, especially in dry ecosystems, savannas and mountain fields, which may hold numerous undiscovered secrets about these interactions. We encourage young biologists to engage in natural history observations and to perform manipulative experiments directly in the field to understand the true nature of these successful ant‐pollinations.

Pollination of Richea dracophylla (Ericaceae) and the role of the nocturnal ant Notoncus hickmani (Formicinae)

AbstractOur observation of large numbers of ants Notoncus hickmani (Formicinae) on the flowers of a Tasmanian endemic shrub Richea dracophyllum (Ericacea) during the night in winter prompted us to carry out a more extensive study of pollination of R. dracophyllum at two sites. Terminal panicles bear inflorescences of 300+ flowers whose petals are fused into calyptrae covering the reproductive organs, and the calyptrae must be removed before pollination can occur. To exclude birds, we placed mesh bags over some inflorescences. Inflorescences with exclusion bags had a high proportion of retained calyptra and the numbers of viable seeds were greatly reduced. We found R. dracophyllum to have a very long flowering period (more than 6 months) and a range of floral visitors, including honey‐eaters (Meliphagidae) and flying insects. At one site we observed large numbers (up to 100) of N. hickmani on inflorescences between dusk and midnight during winter at air temperatures down to 2.5°C. They fed on nectar from flowers that had lost their calyptra where they were exposed to pollen from the anthers and scanning electron microscopy showed high numbers of pollen grains being carried on the ants. The feeding behaviour of these ants would facilitate pollination between adjacent flowers (geitonogamy). Smaller numbers of dolichoderine ants (Iridomyrmex bicknelli?) were observed during the daytime in spring but mainly fed under partially detached calyptrae where they had little exposure to pollen. We suggest that R. dracophylla is pollinated by a range of species and functional groups—birds, flying insects and ants, and that the pollinating species will vary during the year and between sites, although insects depend on birds to remove the calyptrae. Ant pollination is rare, nocturnal ant pollination is extremely rare, and pollination by nocturnal cryophilic ants has not been documented previously.

Ants are more than just curious bystanders to some flowers-they act as significant pollinators.

Ant-plant associations are ubiquitous and highly diverse in almost all terrestrial environments, resulting in complex ecological networks. Although ant-plant mutualism is prevalent, ant-mediated pollination is uncommon, and only a few investigations have demonstrated their role in pollination. Thus, the topic of ant-mediated pollination requires revision to assess its significance in pollination biology. Ants are frequent floral visitors, but their impact on plant reproductive fitness is rarely acknowledged; nonetheless, numerous flower-visiting ants have been investigated for their involvement in promoting floral development and hybrid vigor in crops. In this study, we present a summary of the scientific literature published over the last four decades on ants' involvement in pollination, the diversity of pollinating ants to various host plants, the ant-plant pollinating networks, and seasonal patterns of ant-mediated pollination. Ants generally forage for flowers in quest of nectar and other sustenance, and in doing so they pollinate the flowers that they encounter. This review identified the pollination networks between ants and plants at the species and family levels. Pollination is often affected by a number of aspects, including the flower's sex, its ovary position, the inflorescence it bears, and the time of year. The available literature demonstrates that ants visit the inflorescences of the same species only to promote cross-pollination, a process known as "geitonogamy"; however, we conclude that ants may visit different inflorescences of different plants in the field. If ant pollination is the norm, there is less selection pressure to acquire self-compatibility; nonetheless, ants' cross-pollination may have caused ants to co-evolve with the pollinating flowers. This indicates that ants are more than just curious bystanders to some flowers; they act as significant pollinators.

The pollination ecology of Phemeranthus punae (Montiaceae) in southern Bolivia

Phemeranthus punae (R.E.Fr.) Eggli & Nyffeler (Montiaceae) is a perennial geophytic herb from the pre-Puna vegetation in the Andes of south-west Bolivia and north-west Argentina. Flowering plants have been observed for several seasons. Flowers are almost exclusively visited by at least three species of ants (Formicidae: likely Forelius pruinosus Roger, Linepithema sp. and Camponotus bruchi Forel). The ants move freely and rapidly on the plants and switch to neighbouring plants within less than five seconds. Pollen grains adhere to legs and bodies of the ants, which visit the flowers to feed on the nectar. The low stature of P. punae, its horizontally spreading to ascending inflorescences and the small flowers conform to the ant pollination syndrome characteristics formulated by Hickman (1974). It is concluded that the observed ants are the pollinators of the species in the study area.

Ants are effective pollinators of common buckwheat Fagopyrum esculentum

Abstract Proper management of wild pollinators of agricultural crops requires identification of effective pollinator species. Although non‐bee pollinators are gaining increasing attention, small ground‐dwelling insects such as ants are often deemed ineffective. However, our previous study found a positive correlation between ant visitations to flowers and seed set in the distylous crop common buckwheat, suggesting a potential role of ants as effective pollinators. In this study, we aimed to confirm the effectiveness of ant pollination by conducting ant‐exclusion experiments in the field. In addition, as evidence that ants can transfer pollen, we also counted the number of pollen grains attached to the body surface of two abundant flower‐visiting ant species, Formica japonica and Camponotus japonicus. Under the ant‐exclusion treatment, the buckwheat plants showed a significant reduction (30% on average) in seed set compared with control plants, and this effect was consistent across both flower morphs (pin and thrum) and two seasons (summer and autumn). Moreover, pollen grains of each flower morph were found on both ant species visiting both types of flower, suggesting a potential contribution to seed set in buckwheat. The results of this study suggest that ants may be an underappreciated pollinator of common buckwheat.

Mixed pollination system and floral signals of Paepalanthus (Eriocaulaceae): insects and geitonogamy ensure high reproductive success.

Eriocaulaceae exhibit a great variety of floral traits associated with insect (e.g. nectariferous structures) and wind pollination (unisexual flowers, exposed sexual organs and small pollen grains), as well as the 'selfing syndrome' (small flowers, short distance between stigma and anthers, and temporal overlap of male and female phases). Paepalanthus bifidus, P. subtilis and P. tortilis are related species that differ in form, size and colour of floral structures. We aimed to investigate the pollination and reproductive biology of these three species. We analysed the floral biology, floral visitors, pollinator behaviour, and the contribution of insects, wind and spontaneous geitonogamy to fruit set. We also evaluated the floral colour and scent of the species. Colour reflectance of capitula of each species was measured and plotted in models of insect vision. Floral scent samples were extracted and the compounds were compared to vegetative scent samples. In all species, the staminate and pistillate flowers are arranged in alternating cycles with a temporal overlap between these phases. Ants were the most frequent floral visitors and were effective pollinators in P. bifidus and P. tortilis, while flies were occasional pollinators in P. tortilis. Floral visitors were not observed in P. subtilis. In all species, fruits were produced by spontaneous geitonogamy, with no evidence of wind pollination. According to the models of insect vision, the colours of the capitula of P. bifidus and P. subtilis are the most inconspicuous for ants and flies. We found no difference between the emission of volatiles of inflorescences and vegetative structures. This study suggests that ant pollination might be more widespread in Eriocaulaceae than currently assumed. Furthermore, for small monocarpic plants, mixed mating strategies are most favourable, by ensuring reproduction either by outcrossing when pollinators are abundant or by spontaneous geitonogamy when pollinations are scarce/absent.

In search of unusual interactions. A commentary on: 'Pollen adaptation to ant pollination: a case study from the Proteaceae'.

This article comments on: Nicola Delnevo, Eddie J van Etten, Nicola Clemente, Luna Fogu, Evelina Pavarani, Margaret Byrne and William D Stock, Pollen adaptation to ant pollination: a case study from the Proteaceae, Annals of Botany, Volume 126, Issue 3, 1 September 2020, Pages 377–389, https://doi.org/10.1093/aob/mcaa058.

Pollen adaptation to ant pollination: a case study from the Proteaceae.

Background and AimsAnt–plant associations are widely diverse and distributed throughout the world, leading to antagonistic and/or mutualistic interactions. Ant pollination is a rare mutualistic association and reports of ants as effective pollinators are limited to a few studies. Conospermum (Proteaceae) is an insect-pollinated genus well represented in the south-western Australia biodiversity hotspot, and here we aimed to evaluate the role of ants as pollinators of C. undulatum.MethodsPollen germination after contact with several species of ants and bees was tested for C. undulatum and five co-flowering species for comparison. We then sampled the pollen load of floral visitors of C. undulatum to assess whether ants carried a pollen load sufficient to enable pollination. Lastly, we performed exclusion treatments to assess the relative effect of flying- and non-flying-invertebrate floral visitors on the reproduction of C. undulatum. For this, we measured the seed set under different conditions: ants exclusion, flying-insects exclusion and control.Key ResultsPollen of C. undulatum, along with the other Conospermum species, had a germination rate after contact with ants of ~80 % which did not differ from the effect of bees; in contrast, the other plant species tested showed a drop in the germination rate to ~10 % following ant treatments. Although ants were generalist visitors, they carried a pollen load with 68–86 % of suitable grains. Moreover, ants significantly contributed to the seed set of C. undulatum.ConclusionsOur study highlights the complexity of ant–flower interactions and suggests that generalizations neglecting the importance of ants as pollinators cannot be made. Conospermum undulatum has evolved pollen with resistance to the negative effect of ant secretions on pollen grains, with ants providing effective pollination services to this threatened species.

Tales of the unexpected – ant pollination mutualism

Tales of the unexpected – ant pollination mutualism

Ant pollination of Paepalanthus lundii (Eriocaulaceae) in Brazilian savanna.

Ant-plant associations are widely diverse and distributed throughout the world, leading to complex ecological networks. Regarding ant-plant mutualism, ant pollination is a very rare interaction and few studies have shown the role of ants as pollinators. Therefore, we aimed to evaluate the role of ants as effective pollinators of Paepalanthus lundii (Eriocaulaceae) in a Brazilian savanna. Fieldwork with experimental manipulation was conducted to evaluate the fitness of P. lundii, considering potential pollinators. For this, we mainly observed the number of seeds produced in different conditions: control, ant exclusion, exclusion of flying insects, and exclusion (entomophily test) of both ants and flying insects. Furthermore, we evaluated all floral visitors throughout the day, stigma receptivity, the numbers of male and female flowers, and patterns of species co-occurrence, which can indicate the presence of different pollinators in the plants at the same time. We observed a relation between seed production and ant visits; Camponotus crassus was the most frequent floral visitor and the most effective pollinator. Also, we observed a statistical difference between the numbers of male and female flowers produced, with a greater number of male flowers. Furthermore, P. lundii presented flowering asynchrony, with 12 different types of maturation sequence, which indicates a cross-pollination system. Lastly, we observed an overlap of the greatest abundance of C. crassus and the time of plant stigmatic receptivity, and a pattern of non co-occurrence of ants, which shows the pollinator role of this ant. Our data provide evidence that previous generalizations neglecting the importance of ants as pollinators are wrong. Brazilian savanna can reveal a lot about the ant-pollination syndrome, since this environment presents peculiar characteristics related to this association. Thus, this study has great significance for the understanding of the ant-pollination syndrome, and for the understanding of the complex ecological networks present in these dry arid systems.

Ants contribute to pollination but not to reproduction in a rare calcareous grassland forb.

The number of plants pollinated by ants is surprisingly low given the abundance of ants and the fact that they are common visitors of angiosperms. Generally ants are considered as nectar robbers that do not provide pollination service. We studied the pollination system of the endangered dry grassland forb Euphorbia seguieriana and found two ant species to be the most frequent visitors of its flowers. Workers of Formica cunicularia carried five times more pollen than smaller Tapinoma erraticum individuals, but significantly more viable pollen was recovered from the latter. Overall, the viability of pollen on ant cuticles was significantly lower (p < 0.001)—presumably an antibiotic effect of the metapleural gland secretion. A marking experiment suggested that ants were unlikely to facilitate outcrossing as workers repeatedly returned to the same individual plant. In open pollinated plants and when access was given exclusively to flying insects, fruit set was nearly 100%. In plants visited by ants only, roughly one third of flowers set fruit, and almost none set fruit when all insects were excluded. The germination rate of seeds from flowers pollinated by flying insects was 31 ± 7% in contrast to 1 ± 1% resulting from ant pollination. We conclude that inbreeding depression may be responsible for the very low germination rate in ant pollinated flowers and that ants, although the most frequent visitors, play a negligible or even deleterious role in the reproduction of E. seguieriana. Our study reiterates the need to investigate plant fitness effects beyond seed set in order to confirm ant-plant mutualisms.

Complex flowers and rare pollinators: Does ant pollination in Ditassa show a stable system in Asclepiadoideae (Apocynaceae)?

If on one hand, ant pollination is rare, on the other Asclepiadoideae flowers are the most complex among Eudicots. Both themes are exciting in pollination biology. Although there are records of ants with the ability to remove the pollinarium on this subfamily, the role of these insects as pollinators is not yet known. Therefore, we investigated the interaction between flowers and ants, as well as the associated features in two species of Asclepiadoideae, Ditassa capillaris and D. hastata. The studied species were both visited by Cephalotes inaequalis and Dorymyrmex thoracicus. We analyzed the common traits of ant pollination of the plant species, recorded the number of visit by ants, and carried out experiments of selective pollination, developing an effectivity index. Both Ditassa species have common traits of ant pollination, such as small bright flowers with exposed floral resource. The pollinarium is clip-shaped and resistant to the metapleural gland, which ensures effective pollination. Dorymyrmex thoracicus is a very frequent but not very efficient pollinator, whereas Cephalotes inaequalis is more efficient though at a lower frequency. Therefore, the total contributions of both ants to the pollination of both Ditassa species are similar. The features of both Ditassa species which favor ant pollination, include some synapomorphies within Asclepiadoideae. Furthermore, the efficiency of the ants as pollinators to the reproductive success of the plants was similar despite the different behaviors observed in both ant species. Hence, we suggest that the role of ants in pollination within this subfamily has been neglected.

Ants as floral visitors of Blutaparon portulacoides (A. St-Hil.) Mears (Amaranthaceae): an ant pollination system in the Atlantic Rainforest

Ant pollination is a debated topic that requires more attention in order to clarify the role of ants as potential pollinators. Although many authors consider ants as mere nectar robbers, there are studies proving that ants may act as pollinators and that some plants even have flower traits acting as ant attractors. In this study, we evaluated the role of the ants in pollination of Blutaparon portulacoides inflorescences. This plant species has most of the traits favorable for ant pollination, such as short and aggregated inflorescences, and synchronized blooming as well as growing in an environment where ant pollination is likely to occur. Our results show that ants are the most abundant visitors throughout the day and that there is no effect of ant integument on pollen germination. Furthermore, the flower visitor exclusion experiment showed that ants have a role in the pollination of B. portulacoides by promoting seed formation. Ants can have an important part in the pollination of B. portulacoides in a scenario where winged insects are absent or scarce.

Floral volatiles play a key role in specialized ant pollination

a b s t r a c t Chemical signals emitted by plants are crucial to understand the ecology and evolution of plant-animal interactions. Scent is an important component of floral phenotype and represents a decisive commu- nication channel between plants and floral visitors. Floral volatiles promote attraction of mutualistic pollinators and, in some cases, serve to prevent flower visitation by antagonists such as ants. Despite ant visits to flowers have been suggested to be detrimental to plant fitness, in recent years there has been a growing recognition of the positive role of ants in pollination. Nevertheless, the question of whether floral volatiles mediate mutualisms between ants and ant-pollinated plants still remains largely unexplored. Here we review the documented cases of ant pollination and investigate the chemical composition of the floral scent in the ant-pollinated plant Cytinus hypocistis. By using chemical-electrophysiological analyses and field behavioural assays, we examine the importance of olfactory cues for ants, identify compounds that stimulate antennal responses, and evaluate whether these compounds elicit behavioural responses. Our findings reveal that floral scent plays a crucial role in this mutualistic ant-flower interaction, and that only ant species that provide pollination services and not others occurring in the habitat are efficiently attracted by floral volatiles. 4-oxoisophorone, (E)-cinnamaldehyde, and (E)-cinnamyl alcohol were the most abundant compounds in Cytinus flowers, and ant antennae responded to all of them. Four ant pol- linator species were significantly attracted to volatiles emitted by Cytinus inflorescences as well as to synthetic mixtures and single antennal-active compounds. The small amount of available data so far sug- gest that there is broad interspecific variation in floral scent composition among ant-pollinated plants, which could reflect differential responses and olfactory preferences among different ant species. Many exciting discoveries will be made as we enter into further research on chemical communication between ants and plants. © 2013 Elsevier GmbH. All rights reserved.

Why ant pollination is rare: new evidence and implications of the antibiotic hypothesis

The antibiotic hypothesis proposes that ant pollination is rare at least in part because the cuticular antimicrobial secretions of ants are toxic to pollen grains. We tested this hypothesis by comparing the effects of ants and bees on pollen in two regions: a tropical rainforest in Amazonian Peru and temperate forests and old fields in Canada. We found support for three predictions that follow from the antibiotic hypothesis. (1) For all 10 ant and 11 plant species in our study, contact with ants significantly reduced pollen germination, confirming the generality of this effect. (2) Contact with two bee species did not have similar effects; pollen exposed to bees germinated as well as control pollen. (3) Consistent with the presumed greater abundance of entomopathogens in the tropics, which may have selected for stronger antibiotic secretions in tropical ants, tropical ants had more negative effects on pollen than temperate ants. We speculate that the antibiotic hypothesis contributes not only to the rarity but also to the biogeography of ant pollination, and we discuss whether the negative effects of ants on pollen have resulted in selection for floral defenses against ants.

Floral visitation in the Australian native shrub genus Acrotriche R.Br (Ericaceae): an abundance of ants (Formicidae)

AbstractThe genus Acrotriche is a group of predominantly winter flowering Australian native plants with small flowers that use a unique method of secondary pollen presentation. The mating system of one species has been determined as requiring transfer of pollen from one plant to another to enable effective pollination and floral conformity in other species suggests similar breeding systems. Previous authors have suggested non‐flying mammal pollination for members of the genus based on floral traits and reports of floral consumption; however, this hypothesis does not stand up to scrutiny. Acrotriche floral traits can also be interpreted as indicative of crawling invertebrate pollination. The identification of floral visitors and their potential for pollination has not been conducted previously for any Acrotriche species. To identify potential pollinators, the floral visitors to six different species of Acrotriche were observed throughout an entire 24 h period at a range of sites throughout South Australia. Ants were identified as the most common and abundant floral visitors for all Acrotriche species. Ant pollination is considered rare due to the negative effects that ant secretions can have on pollen viability. To determine these effects in relation to Acrotriche, pollen germination experiments were undertaken after contact with the integument of several ant species. Reductions in pollen viability varied between plants and ant species but in all experiments viable pollen remained after ant contact. These results, along with observed behaviour of ant visitors, indicate that ants may contribute to pollination in Acrotriche.

Do Native Ants Play a Significant Role in the Reproductive Success of the Rare San Fernando Valley Spineflower, Chorizanthe parryi var. fernandina (Polygonaceae)?

Abstract Previous field studies of the reproductive biology of the San Fernando Valley spineflower, Chorizanthe parryi var. fernandina (S. Watson) Jeps. suggested that pollination by ants might be an important feature of this endangered polygonous taxon. This conclusion was based on observations that native ants were abundant floral visitors and constant to this species. We conducted the current study to explore more closely the possibility that native ants were facilitating pollination and resulting in viable seed set. Based on our data, ants can indeed be effective pollinators of spineflower. Fruit set was 57% higher in flowers exposed to ant visitation, compared to 27% in control flowers where ants were excluded. Further, a 25.7% germination rate was observed for achenes produced in the absence of ants, in contrast to a 61% rate in those produced in the presence of ants. We suggest that ant pollination may be more prevalent in drier climates, ant production of inhibitory substances may not be a severe ...

Chenorchis, a new orchid genus, and its eco-strategy of ant pollination

Chenorchis, a new orchid genus belonging to C. singchii with tropical orchid features, was found in subtropical regions of Gaoligong Mountain in Yunnan Province, China. This taxon undoubtedly belongs to Trib. Vandeae due to its comparatively advanced epiphytic and monopodial characteristics with very hard pollinia and long stipe. It is akin to Ascocentrum and Holcoglossum, from which it differs by its lip lacking appendage, side-lobes arising from both sides of the mid-lobe rather than the entrance to the spur; large stigmatic cave; very large rostellum, conspicuously broader than the column, spreading downward; pollinia each with a distinct caudicle attached to the incurved subterminal portion of a common stipe. Phylogenetic analysis shows that it may be of tropical region originally and evolve into a new genus due to changed environment, indicating that the main motivation of angiosperm differentiation is to bring forth more ecological opportunities. A further examination of reproductive ecology, especially pollination mechanism and breeding system, proved that this species has formed many mechanisms to promote selfing and inbreeding, such as symbiosis with ants ( Temnothorax sp.), utilization of ants for short-distant pollination, opening of flowers simultaneously to increase the frequency of geitonogamy, efficient dispersal and growth of seeds, and crowded communities to improve the possibility of inbreeding. All the adaptive changes above turn into necessary conditions for their survival in subtropical regions. The reproductive strategy of this unique life history shows that this immigrant species autonomously passes the genes on to future generations to remain their adaptability, by quickly occupying the habitat. It is a successful strategy in habitat expansion that inflorescence produces a lot of flowers to facilitate geitonogamy, whose significance may extend to provide evidence that the occurrence of plants' sex results from the trade-offs of the fluctuation of habitat in evolution.

The evolution of ant pollination systems

The evolution of ant pollination systems

Experimental study of pollination by ants in Mediterranean high mountain and arid habitats.

In this paper, we report the results of an experimental study on ant pollination of three plant species inhabiting the Mediterranean high mountains (Alyssum purpureum, Arenaria tetraquetra and Sedum anglicum) and four species inhabiting the aridlands (Lepidium subulatum, Gypsophyla struthium, Frankenia thymifolia and Retama sphaerocarpa) of South-eastern Spain. We determined several plant and ant traits, as well as the composition and abundance of the pollinator assemblage. Insects belonging to 29 families and five orders visited the flowers of the plant species studied. In all but two, L. subulatum and G. struthium, the ants comprised 70-100% of the flower visitors. The results clearly show that five out of seven of these plant species were pollinated by ants. The role of the ants as pollinators seems to depend heavily on the relative abundance of the ants with respect to the other species of the pollinator assemblage, ant pollination becoming evident when ants outnumber other floral visitors. The ant-pollination systems analysed in this study may be the result of prevailing ecological conditions more than an evolutionary result of a specialized interaction.