Eri Yamasaki

Microbial communities on flower surfaces act as signatures of pollinator visitation

Microbes are easily dispersed from one place to another, and immigrant microbes might contain information about the environments from which they came. We hypothesized that part of the microbial community on a flowers surface is transferred there from insect body surfaces and that this community can provide information to identify potential pollinator insects of that plant. We collected insect samples from the field, and found that an insect individual harbored an average of 12.2 × 105 microbial cells on its surface. A laboratory experiment showed that the microbial community composition on a flower surface changed after contact with an insect, suggesting that microbes are transferred from the insect to the flower. Comparison of the microbial fingerprint approach and direct visual observation under field condition suggested that the microbial community on a flower surface could to some extent indicate the structure of plant–pollinator interactions. In conclusion, species-specific insect microbial communities specific to insect species can be transferred from an insect body to a flower surface, and these microbes can serve as a “fingerprint” of the insect species, especially for large-bodied insects. Dispersal of microbes is a ubiquitous phenomenon that has unexpected and novel applications in many fields and disciplines.

Wind and insect pollination (ambophily) of Mallotus spp. (Euphorbiaceae) in tropical and temperate forests

Relatively few flowering plants show ambophily (pollination by both wind and insects), and whether and when ambophily is advantageous has not been studied well. In the present study, we report ambophily in two dioecious pioneer tree species, Mallotus japonicus Mull.Arg. in a temperate forest of Japan, and Mallotus wrayi King ex Hook.f. in a tropical forest of Borneo, and discuss the conditions that contribute to the maintenance of ambophily. Both species are pollinated by wind because they set fruits even when flower visitors were excluded and because substantial amounts of airborne pollen reached female trees. Insects may also contribute to fruit set, because insects with body pollen visited female inflorescences. Because M. japonicus and M. wrayi exhibit floral characteristics that are adapted to both wind and insect pollination, ambophily may be actively maintained in the two species at the study sites and perhaps elsewhere. Whereas previous studies have indicated that ambophily is advantageous for pioneer plants because of changing wind conditions during forest succession, our preliminary data suggest that changes in population density also contribute to the maintenance of ambophily in M. japonicus.

Production of food bodies on the reproductive organs of myrmecophytic Macaranga species (Euphorbiaceae): effects on interactions with herbivores and pollinators

In protective ant–plant mutualisms, plants offer ants food (such as extrafloral nectar and/or food bodies) and ants protect plants from herbivores. However, ants often negatively affect plant reproduction by deterring pollinators. The aggressive protection that mutualistic ants provide to some myrmecophytes may enhance this negative effect in comparison to plant species that are facultatively protected by ants. Because little is known about the processes by which myrmecophytes are pollinated in the presence of ant guards, we examined ant interactions with herbivores and pollinators on plant reproductive organs. We examined eight myrmecophytic and three nonmyrmecophytic Macaranga species in Borneo. Most of the species studied are pollinated by thrips breeding in the inflorescences. Seven of eight myrmecophytic species produced food bodies on young inflorescences and/or immature fruits. Food body production was associated with increased ant abundance on inflorescences of the three species observed. The exclusion of ants from inflorescences of one species without food rewards resulted in increased herbivory damage. In contrast, ant exclusion had no effect on the number of pollinator thrips. The absence of thrips pollinator deterrence by ants may be due to the presence of protective bracteoles that limit ants, but not pollinators, from accessing flowers. This unique mechanism may account for simultaneous thrips pollination and ant defense of inflorescences.

Diversity and evolution of pollinator rewards and protection by Macaranga (Euphorbiaceae) bracteoles

Flowering plants have modified their floral organs in remarkably diverse ways to optimize their interaction with pollinators. Although floral organs represent a major source of floral diversity, many plants also use extrafloral organs, such as bracts and bracteoles, in interacting with pollinators; however, the evolutionary dynamics of non-floral organs involved in pollination are poorly studied. The genus Macaranga is characterized by protective mutualisms with ants that potentially interfere with pollinators on flowers. Macaranga flowers lack perianths and, notably, bracteoles serve the dual function of rewarding pollinators and protecting them from guarding ants; in one group of species, bracteoles provide a nectar reward to generalist pollinators, while in another group, bracteole “chambers” protect thrips or hemipteran pollinators that use these structures as feeding and breeding sites. We examined the diversity and evolutionary dynamics of inflorescence morphology in Macaranga, focusing on bracteoles. We recognized three inflorescence types based on examination of herbarium materials: Discoid-gland, which possess disc-shaped glands on the bracteole surfaces (including all the generalist-pollinated species); Enclosing, in which bracteoles cover flowers (including all the thrips- and hemipteran-pollinated species); and Inconspicuous, in which bracteoles are small, narrow or absent. Ancestral state reconstruction indicated that inflorescence morphologies have changed multiple times in the genus. These findings suggest that morphological changes in non-floral characters (bracteoles) of Macaranga species have occurred as frequently as in the floral structures of many flowering plants. The multiple evolutions of the Enclosing bracteoles, which protect pollinators, might have been facilitated by pollination interference from mutualistic ants.

8 million phenological and sky images from 29 ecosystems from the Arctic to the tropics: the Phenological Eyes Network

We report long-term continuous phenological and sky images taken by time-lapse cameras through the Phenological Eyes Network (http://www.pheno-eye.org. Accessed 29 May 2018) in various ecosystems from the Arctic to the tropics. Phenological images are useful in recording the year-to-year variability in the timing of flowering, leaf-flush, leaf-coloring, and leaf-fall and detecting the characteristics of phenological patterns and timing sensitivity among species and ecosystems. They can also help interpret variations in carbon, water, and heat cycling in terrestrial ecosystems, and be used to obtain ground-truth data for the validation of satellite-observed products. Sky images are useful in continuously recording atmospheric conditions and obtaining ground-truth data for the validation of cloud contamination and atmospheric noise present in satellite remote-sensing data. We have taken sky, forest canopy, forest floor, and shoot images of a range of tree species and landscapes, using time-lapse cameras installed on forest floors, towers, and rooftops. In total, 84 time-lapse cameras at 29 sites have taken 8 million images since 1999. Our images provide (1) long-term, continuous detailed records of plant phenology that are more quantitative than in situ visual phenological observations of index trees; (2) basic information to explain the responsiveness, vulnerability, and resilience of ecosystem canopies and their functions and services to changes in climate; and (3) ground-truthing for the validation of satellite remote-sensing observations.

Modified leaves with disk-shaped nectaries of Macaranga sinensis (Euphorbiaceae) provide reward for pollinators

UNLABELLED PREMISE OF THE STUDY Nectar is the most common reward provided by animal-pollinated flowers. Diversity in position and structure of floral nectaries suggests that floral nectar production evolved repeatedly, but the evolutionary origins are not well known. Flowers of the genus Macaranga (Euphorbiaceae) are apetalous and lack floral nectar. Nevertheless, many Macaranga species possess disk-shaped nectaries on their leaves, sought by ants that defend plants from herbivory. In some Macaranga species, similar glands also occur on the bracteoles-modified leaves subtending the flowers. We investigated whether these glands on the bracteoles of M. sinensis are involved in pollination. • METHODS Flower visitors were captured, and body pollen was examined. The behavior of flower visitors on inflorescences was also observed. Sugar composition of the nectar from bracteoles and leaves was collected and analyzed using high-performance liquid chromatography. • KEY RESULTS Various bees and flies with body pollen visited both male and female inflorescences, feeding on nectar from the bracteoles and touching anthers and stigmas in the process. Sugar composition of nectar from the bracteoles and the leaves did not differ. • CONCLUSIONS Macaranga sinensis was pollinated by insects foraging on the disk-shaped nectaries on bracteoles. The similar appearance, position, and sugar composition of nectar suggest that disk-shaped nectaries on bracteoles and leaves are homologous and that nectaries on leaves were recruited to inflorescences to serve floral function in M. sinensis. Having protective mutualism with ants has likely opened an unusual route for the evolution of floral nectar in otherwise non-nectar-producing flowers of M. sinensis.

Ant-Repelling Pollinators of the Myrmecophytic Macaranga winkleri (Euphorbiaceae)

Many plants have mutualistic relationships with ants, whereby plants provide food and/or nesting sites for the symbiotic ants, and in turn the ants protect the host plants by excluding herbivores. While the ants are useful as guards, they may negatively affect host reproduction by excluding pollinators. Here we studied this potential conflict in the myrmecophytic Macaranga winkleri pollinated by the thrips Dolichothrips fialae. Behavioural responses of ant guards to pollinator thrips and their chemicals, and related chemical analyses, provide evidence that thrips deter ant-guards by secreting droplets containing ant-repelling n-decanoic acid from their anuses. This is the first report of insect pollinators repelling their host’s symbiotic guard ants to perform pollination. This is a novel strategy by which a plant host avoids interference with pollination by ant-guards in an ant–plant mutualism. The acquisition of a pollination system that is resistant to ant attacks may have facilitated the evolution of myrmecophytes in the genus Macaranga.