FLORAL SCENT IN A WHOLE-PLANT CONTEXT Floral volatiles controlling ant behaviour

Summary 1. Ants show complex interactions with plants, both facultative and mutualistic, ranging from grazers through seed predators and dispersers to herders of some herbivores and guards against others. But ants are rarely pollinators, and their visits to flowers may be detrimental to plant fitness. 2. Plants therefore have various strategies to control ant distributions, and restrict them to foliage rather than flowers. These 'filters' may involve physical barriers on or around flowers, or 'decoys and bribes' sited on the foliage (usually extrafloral nectaries -EFNs). Alternatively, volatile organic compounds (VOCs) are used as signals to control ant behaviour, attracting ants to leaves and ⁄ or deterring them from functional flowers. Some of the past evidence that flowers repel ants by VOCs has been equivocal and we describe the shortcomings of some experimental approaches, which involve behavioural tests in artificial conditions. 3. We review our previous study of myrmecophytic acacias, which used in situ experiments to show that volatiles derived from pollen can specifically and transiently deter ants during dehiscence, the effects being stronger in ant-guarded species and more effective on resident ants, both in African and Neotropical species. In these plants, repellence involves at least some volatiles that are known components of ant alarm pheromones, but are not repellent to beneficial bee visitors. 4. We also present new evidence of ant repellence by VOCs in temperate flowers, which is usually pollen-based and active on common European ants. We use these data to indicate that across a wide range of plants there is an apparent trade-off in ant-controlling filter strategies between the use of defensive floral volatiles and the alternatives of decoying EFNs or physical barriers

The diversity and evolution of pollination systems in large plant clades: Apocynaceae as a case study

Background and Aims Large clades of angiosperms are often characterized by diverse interactions with pollinators, but how these pollination systems are structured phylogenetically and biogeographically is still uncertain for most families. Apocynaceae is a clade of >5300 species with a worldwide distribution. A database representing >10 % of species in the family was used to explore the diversity of pollinators and evolutionary shifts in pollination systems across major clades and regions. Methods The database was compiled from published and unpublished reports. Plants were categorized into broad pollination systems and then subdivided to include bimodal systems. These were mapped against the five major divisions of the family, and against the smaller clades. Finally, pollination systems were mapped onto a phylogenetic reconstruction that included those species for which sequence data are available, and transition rates between pollination systems were calculated. Key Results Most Apocynaceae are insect pollinated with few records of bird pollination. Almost three-quarters of species are pollinated by a single higher taxon (e.g. flies or moths); 7 % have bimodal pollination systems, whilst the remaining approx. 20 % are insect generalists. The less phenotypically specialized flowers of the Rauvolfioids are pollinated by a more restricted set of pollinators than are more complex flowers within the Apocynoids + Periplocoideae + Secamonoideae + Asclepiadoideae (APSA) clade. Certain combinations of bimodal pollination systems are more common than others. Some pollination systems are missing from particular regions, whilst others are over-represented. Conclusions Within Apocynaceae, interactions with pollinators are highly structured both phylogenetically and biogeographically. Variation in transition rates between pollination systems suggest constraints on their evolution, whereas regional differences point to environmental effects such as filtering of certain pollinators from habitats. This is the most extensive analysis of its type so far attempted and gives important insights into the diversity and evolution of pollination systems in large clades

The effects of insect visitation on floral colour change

This study investigated the effects of flower visitation on floral colour change and the subsequent influence of such change on insect foraging behaviour. Colour change was examined in six plant species; Myosotis sylvatica, Echium vulgare and Lonicera periclymenum were studied locally to St. Andrews, Fife, Scotland and Echium judaeum, Lupirtus pilosus and Alkanna orientalis were studied in various locations in the eastern Mediterranean region. Patterns of colour change were recorded both with natural insect visitation allowed and excluded, to establish whether the rate of colour change could be altered through visitation per se or rate of visitation. Detailed observation of the flower handling characteristics of all visiting insects allowed artificial floral manipulations to be devised that simulated the different aspects of visitor behaviour. This enabled the effects of simple mechanical handling on colour change to be separated from those of pollen deposition and post pollination events. Floral reward was measured in relation to flower colour phases to assess whether the change in colour was acting as a functional signal to flower visitors; insect choice of flower colour was noted, to determine whether reward status affected foraging behaviour. One or more factors significantly altered the characteristics of colour change in all species except Lonicera periclymenum. The triggering factor could be the exclusion of visitors, rate of natural visitation, floral manipulation, or aspects of the pollination process. In Lupinus pilosus pollen deposition and/or pollen tube growth was the trigger for colour change. Pollen deposition was also the most likely trigger in both Alkanna orientalis and Myosotis sylvatica, although the varied patterns of colour change in these species could be related to wound responses and/or senescence. Pollination processes were not involved in colour change in either species of Echium. The first recorded example of a 'reverse' colour change is reported fox Echiumjudaeum. Floral reward varied between colour phases in all plants except Echium vulgare, and visiting insects did not show any bias towards particular flower colour phases in this plant. In all other species a variety of flies and bees visited the most rewarding colour phase preferentially. A model is presented that incorporates all influences on floral colour change in a single framework, potentially unifying the concepts of age-related' and 'inducible' change which have previously been thought to be distinct

Aggressive displacement of <i>Xylocopa nigrita</i> carpenter bees from flowers of <i>Lagenaria sphaerica</i> (Cucurbitaceae) by territorial male Eastern Olive Sunbirds (<i>Cyanomitra olivacea</i>) in Tanzania

<p>Male Eastern Olive Sunbirds (<i>Cyanomitra</i> <i>olivacea</i>) and <i>Xylocopa nigrita</i> carpenter bees in Tanzania both utilise the flowers of male plants of <i>Lagenaria sphaerica</i> (Cucurbitaceae) as a source of nectar. The sunbirds set up territories defending this nectar resource. Observations of interactions between the sunbirds and the carpenter bees show that the bees are aggressively displaced from flowers when spotted by the birds. Only the bees can be considered as legitimate pollinators as the birds do not contact the anthers of the male flowers and were never seen visiting nectarless female flowers of <i>Lagenaria sphaerica</i>. Such territory defence may have implications for the frequency of movement and composition of pollen being transferred from male to female flowers which warrants further research.</p

Aggressive displacement of Xylocopa nigrita carpenter bees from flowers of Lagenaria sphaerica (Cucurbitaceae) by territorial male Eastern Olive Sunbirds (Cyanomitra olivacea) in Tanzania

Male Eastern Olive Sunbirds (Cyanomitra olivacea) and Xylocopa nigrita carpenter bees in Tanzania both utilise the flowers of male plants of Lagenaria sphaerica (Cucurbitaceae) as a source of nectar. The sunbirds set up territories defending this nectar resource. Observations of interactions between the sunbirds and the carpenter bees show that the bees are aggressively displaced from flowers when spotted by the birds. Only the bees can be considered as legitimate pollinators as the birds do not contact the anthers of the male flowers and were never seen visiting nectarless female flowers of Lagenaria sphaerica. Such territory defence may have implications for the frequency of movement and composition of pollen being transferred from male to female flowers which warrants further research

Hoverfly visitation in relation to floral colour change (Diptera : Syrphidae)

Flower visitors from several insect taxa (bees, butterflies and some flies) are known to forage assortatively at flowers where floral colour change has occurred; these alterations are often dramatic and the flowers are retained on the plant. Here, a further example of floral colour change is reported and, for the first time, demonstrated how the incidence of such alteration affects foraging in syrphid flies. Feeding behaviour in Rhingia campestris and at least two other hoverfly species is strongly influenced by a striking and extremely localised colour change in the flowers of the wood forget-me-not, Myosotis sylvatica. Nearly 99% of flower visits to pre-change flowers elicited a feeding response whereas only 13 % of visits to post-change flowers led to the same behaviour. Feeding times at post-change flowers were 2-3 times shorter compared to pre-colour-change residence time. Additionally, we confirm centrifugation as a suitable method for extracting low volumes of nectar from small tubular flowers; the change in syrphid feeding behaviour corresponds with both colour change and floral reward status.</p

Determinants of Contests in Ugandan Female Ground-Nesting Bees (Tetralonia sp. n.)

Many animals engage in contests with conspecifics for access to resources. Understanding which resources individuals are contesting for, and what influences the outcome is central to our understanding of contest behaviour. We initially observed female bees of the genus Tetralonia (sp. n.) aggressively competing for access to burrows in the ground, without any clear indication of exactly which resources were being contested, or what factors might predict the outcome.We then individually marked bees and assigned ownership of burrows to individuals, before observing over 100 aggressive interactions. After excavating burrows cast with molten wax, we concluded that burrows were nests for provisioning larvae. We found that ownership (as putatively designated by us) had no influence on contest outcome, but rather that the position of the bees in the burrow was decisive; whichever bee was already in the burrowwhenthe contest beganwonthe vast majority of interactions. Furthermore, bees that were designated ownership of a burrow did not engage in longer fights for possession of that specific burrow, indicating either that they were not committing any kind of 'Concorde fallacy' by basing decisions on past investment, or that the assignment of ownership was incorrect. Instead, fights were longer later in the day, presumably as the value of the burrow as a refuge from the cold and/or predation increased as night approached. Nest parasitism does not seem to be a common strategy in this species, as owners were not more likely to attempt ejecting an intruder than vice versa. This indicates that contest settlement may not always follow theoretical predictions, but rather that insights and inferences into a species' ecology can be made from observations of dyadic contests

Pollination ecology of Desmodium setigerum (Fabaceae) in Uganda; do big bees do it better?

Explosive pollen release is documented in many plant families, including the Fabaceae. Desmodium setigerum E. Mey (Fabaceae) is a perennial herb with single trip explosive pollen release found in eastern Africa, and the unique ability to reverse floral colour change if insufficient pollination has occurred. However, little else is known about the pollination ecology of this species, what visitors can trigger explosive pollen release, and whether bee body size is related to pollination efficiency. We investigated: 1) the breeding system of D. setigerum, and whether it is pollen limited; 2) whether flowers are visited early in the day allowing sufficient time for a second opportunity for pollination; and 3) what insect species visit D. setigerum and the relative efficacy of different flower visitors in relation to visitor size and pollination success. We found that although self-compatible, D. setigerum requires insect visitation to set seed as explosive pollen release is needed even for selfing. Most flowers are initially visited before 1400h, and by 1800h nearly all flowers have been tripped. Flowers were not pollen limited in this study, and were visited primarily by bees. We observed 16 visiting species, and there was a wide variation (0-404 grains) in the amount of pollen deposited on stigmas. Although almost all bees deposited some pollen, the mean number of pollen grains deposited in a single visit per species was negatively related to body size. However, one particular megachilid species deposited significantly more pollen grains than any other visitor and so is likely an important pollinator of this species. This provides insights into the pollination biology of this unique plant species, and adds to increasing literature on the relationships between bee body size, explosive pollen release and pollination effectiveness