No evidence of carbon storage usage for seed production in 18 dipterocarp masting species in a tropical rain forest.

Most canopy species in lowland tropical rain forests in Southeast Asia, represented by Dipterocarpaceae, undergo mast reproduction synchronously at community level during a general flowering event. Such events occur at irregular intervals of 2-10 years. Some species do not necessarily participate in every synchronous mast reproduction, however. This may be due to a lack of carbohydrate resources in the trees for masting. We tested the hypothesis that interspecific differences in the time required to store assimilates in trees for seed production are due to the frequency of masting and/or seed size in each species. We examined the relationship between reproductive frequency and the carbon accumulation period necessary for seed production, and between the seed size and the period, using radiocarbon analysis in 18 dipterocarp canopy species. The mean carbon accumulation period was 0.84 years before seed maturation in all species studied. The carbon accumulation period did not have any significant correlation with reproductive frequency or seed size, both of which varied widely across the species studied. Our results show that for seed production, dipterocarp masting species do not use carbon assimilates stored for a period between the masting years, but instead use recent photosynthates produced primarily in a masting year, regardless of the masting interval or seed size of each species. These findings suggest that storage of carbohydrate resources is not a limiting factor in the masting of dipterocarps, and that accumulation and allocation of other resources is important as a precondition for participation in general flowering.

Elevated luminal inorganic phosphate suppresses intestinal Zn absorption in 5/6 nephrectomized rats.

Zinc (Zn) is an essential trace element in various biological processes. Chronic kidney disease (CKD) often leads to hypozincemia, resulting in further progression of CKD. In CKD, intestinal Zn absorption, the main regulator of systemic Zn metabolism, is often impaired; however, the mechanism underlying Zn malabsorption remains unclear. Here, we evaluated intestinal Zn absorption capacity in a rat model of CKD induced by 5/6 nephrectomy (5/6 Nx). Rats were given Zn and the incremental area under the plasma Zn concentration-time curve (iAUC) was measured as well as the expression of ZIP4, an intestinal Zn transporter. We found that 5/6 Nx rats showed lower iAUC than sham-operated rats, but expression of ZIP4 protein was upregulated. We therefore focused on other Zn absorption regulators to explore the mechanism by which Zn absorption was substantially decreased. Because some phosphate compounds inhibit Zn absorption by coprecipitation and hyperphosphatemia is a common symptom in advanced CKD, we measured inorganic phosphate (Pi) levels. Pi was elevated in not only serum but also the intestinal lumen of 5/6 Nx rats. Furthermore, intestinal intraluminal Pi administration decreased the iAUC in a dose-dependent manner in normal rats. In vitro, increased Pi concentration decreased Zn solubility under physiological conditions. Furthermore, dietary Pi restriction ameliorated hypozincemia in 5/6 Nx rats. We conclude that hyperphosphatemia or excess Pi intake is a factor in Zn malabsorption and hypozincemia in CKD. Appropriate management of hyperphosphatemia will be useful for prevention and treatment of hypozincemia in patients with CKD.NEW & NOTEWORTHY We demonstrated that elevated intestinal luminal Pi concentration can suppress intestinal Zn absorption activity without decreasing the expression of the associated Zn transporter. Increased intestinal luminal Pi led to the formation of an insoluble complex with Zn while dietary Pi restriction or administration of a Pi binder ameliorated hypozincemia in chronic kidney disease model rats. Therefore, modulation of dietary Pi by Pi restriction or a Pi binder might be useful for the treatment of hypozincemia and hyperphosphatemia.

Water uptake patterns of tropical canopy trees in Borneo: species-specific and temporal variation and relationships with aboveground traits.

Root water uptake depth and its temporal variation are important determinants of tree mortality, resource partitioning and drought resistance; however, their effects on tropical trees remain poorly understood. In this study, we investigated interspecific differences in water uptake depth and its temporal variation using stable isotope analysis and examined the relationships between water uptake depth and aboveground traits in a humid aseasonal tropical rainforest in Borneo. Species-specific differences in water uptake depth were examined for six dominant dipterocarp species. Temporal variation in water uptake depth for various canopy trees was assessed in three periods with different soil moisture conditions. We then examined the relationships between water uptake depth and aboveground traits including wood density, maximum tree height, flowering frequency and growth rate. Dipterocarpus globosus appeared to be more reliant on deep water resources than the other dipterocarp species. Water uptake from the soil layers varied among the three sampling periods. Trees generally utilized deeper soil water during the second driest sampling period, when temperatures were lowest. During the driest and wettest sampling periods, species with higher flowering frequencies tended to preferentially uptake deep soil water. These results suggest that low temperature and soil moisture promote increased deep soil water uptake in the study region. Dynamic relationships between water uptake patterns and aboveground tree traits may be related to resource partitioning among co-existing species.

Green greenhouse: leaf enclosure for fruit development of an androdioecious vine, Schizopepon bryoniifolius.

Individual plants can produce leaves that differ substantially in size, morphology and many other traits. However, leaves that play a specific role in reproduction have rarely been reported. Here, we report leaves specialized to enclose fruit clusters and enhance seed production in an annual vine, Schizopepon bryoniifolius. Enclosure leaves were produced at the end of the growing season in late autumn. They were different in greenness and structure from other leaves. Under solar radiation, the ambient temperature inside an intact enclosure was up to 4.6°C higher than that near a fruit cluster whose enclosure leaves had been removed. We found that enclosures were thicker at colder sites. Removal of enclosing leaves negatively affected fruit survival and/or growth, but we could not identify the exact mechanism. The results suggested that enclosures allow the plant to produce seeds under the cold weather the plant encounters at the end of its life. Vegetative and reproductive traits of plants have usually been studied separately. This study indicates how they can dynamically interact, as shown by an examination of associations among leaf and reproductive trait changes according to life stages.

Evolutionary stability of plant-pollinator networks: efficient communities and a pollination dilemma.

Mutualistic interactions between species are ubiquitous in nature and essential for ecosystem functioning. Often dozens or even hundreds of species with different degrees of specialisation form complex networks. How this complexity evolves is a fundamental question in ecology. Here, we present a new game theoretical approach to model complex coevolutionary processes and apply it to pollination networks. A theoretical analysis reveals multiple evolutionary stable network structures that depend on the availability of pollination service. In particular, we find efficient communities, in which a high percentage of pollen are transported conspecifically, to evolve only when plant and pollinator abundances are well balanced. Both pollinator shortage and oversupply select for more inefficient network structures. The results suggest that availability of pollination services is a key factor structuring pollination networks and may offer a new explanation for geographical differences in pollination communities that have long been recognised by ecologists.

Long non-coding RNA 2310069B03Rik functions as a suppressor of Ucp1 expression under prolonged cold exposure in murine beige adipocytes.

Specific conditions, such as exposure to cold, can induce the production of brown-like adipocytes in white adipose tissue. These adipocytes express high levels of uncoupling protein 1 (UCP1) and energy expended by generating heat. Thus, these are a potential target for the prevention or treatment of obesity. The present study involved a comprehensive analysis of the adipose tissue to understand the relationship between long non-coding RNA (lncRNA) 2310069B03Rik and UCP1. Cold exposure increased both lncRNA 2310069B03Rik and Ucp1 expression in inguinal white adipose tissue (iWAT). However, overexpression of lncRNA 2310069B03Rik suppressed the Ucp1 mRNA expression and the promoter activity of UCP1 in the iWAT primary adipocytes. In addition, compared to the early induction of Ucp1 expression by cold stimulation, the induction of lncRNA 2310069B03Rik expression was later. These results suggest that lncRNA 2310069B03Rik functions as a suppression factor of Ucp1 expression.

Relativistic redshift of the star S0-2 orbiting the Galactic Center supermassive black hole.

The general theory of relativity predicts that a star passing close to a supermassive black hole should exhibit a relativistic redshift. In this study, we used observations of the Galactic Center star S0-2 to test this prediction. We combined existing spectroscopic and astrometric measurements from 1995-2017, which cover S0-2's 16-year orbit, with measurements from March to September 2018, which cover three events during S0-2's closest approach to the black hole. We detected a combination of special relativistic and gravitational redshift, quantified using the redshift parameter ϒ. Our result, ϒ = 0.88 ± 0.17, is consistent with general relativity (ϒ = 1) and excludes a Newtonian model (ϒ = 0) with a statistical significance of 5σ.

Effects of temporal variation in community-level fruit abundance on seed dispersal by birds across woody species.

PREMISE OF THE STUDY: In animal-dispersed plants, seed dispersal patterns of the same species in the same habitat can greatly differ among individuals and temporally. Many studies have revealed the pervasive effects of spatial variation in fruit abundance on seed dispersal of individual plants. By contrast, very few studies have investigated the temporal variation in seed dispersal. METHODS: We investigated the effects of conspecific and community-level fruit abundance on fruit removal rate and seed dispersal distance of six bird-dispersed woody species in a Japanese temperate forest for 3 yr. The six species share similar fruit characteristics but have different fruiting seasons. In addition, we also considered the effects of bird seasonality in diet and species composition on seed dispersal. KEY RESULTS: Inter-annual and inter-seasonal variation in community-level fruit abundance determined both fruit removal and the seed dispersal distance across species, but the effect differed with seasonal changes in bird behavior. Abundant fruit satiated fruit removal by birds only during fruit-feeding periods, not during insect-feeding periods. A scarcity of fruit increased the dispersal distance, but only during the migratory period. This difference was probably due to the different foraging behaviors of passing migrants and territorial birds. CONCLUSIONS: Our results illustrated that temporal variation in community-level fruit abundance could be a determining factor for seed dispersal in temperate forests. The effects of temporal variations in fruit abundance on seed dispersal patterns should be investigated in other ecosystems in order to understand their importance and associations with frugivore phenology.

Geographical variation in the heterogeneity of mutualistic networks.

Plant-animal mutualistic networks are characterized by highly heterogeneous degree distributions. The majority of species interact with few partner species, while a small number are highly connected to form network hubs that are proposed to play an important role in community stability. It has not been investigated, however, if or how the degree distributions vary among types of mutualisms or communities, or between plants and animals in the same network. Here, we evaluate the degree distributions of pollination and seed-dispersal networks, which are two major types of mutualistic networks that have often been discussed in parallel, using an index based on Pielou's evenness. Among 56 pollination networks we found strong negative correlation of the heterogeneity between plants and animals, and geographical shifts of network hubs from plants in temperate regions to animals in the tropics. For 28 seed-dispersal networks, by contrast, the correlation was positive, and there is no comparable geographical pattern. These results may be explained by evolution towards specialization in the presence of context-dependent costs that occur if plants share the animal species as interaction partner. How the identity of network hubs affects the stability and resilience of the community is an important question for future studies.

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 flower's 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 × 10(5) 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.

Wide host ranges of herbivorous beetles? Insights from DNA bar coding.

There are very few studies that have investigated host-specificity among tropical herbivorous insects. Indeed, most of the trophic interactions of herbivorous insects in Southeast Asian tropical rainforests remain unknown, and whether polyphagous feeding is common in the herbivores of this ecosystem has not been determined. The present study employed DNA bar coding to reveal the trophic associations of adult leaf-chewing chrysomelid beetles in a Bornean rainforest. Plant material ingested by the adults was retrieved from the bodies of the insects, and a portion of the chloroplast rbcL sequence was then amplified from this material. The plants were identified at the family level using an existing reference database of chloroplast DNA. Our DNA-based diet analysis of eleven chrysomelid species successfully identified their host plant families and indicated that five beetle species fed on more than two families within the angiosperms, and four species fed on several families of gymnosperms and/or ferns together with multiple angiosperm families. These findings suggest that generalist chrysomelid beetles associated with ecologically and taxonomically distant plants constitute a part of the plant-insect network of the Bornean rainforest.

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

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.

Variation in the strength of association among pollination systems and floral traits: evolutionary changes in the floral traits of Bornean gingers (Zingiberaceae).

PREMISE OF THE STUDY: Diversification of floral traits in angiosperms is often attributed to have been driven by adaptations to pollinators. Nevertheless, phylogenetic studies on the relationships among evolutionary changes in floral traits and pollination systems are still limited. We examined the relationships between floral trait changes and pollinator shifts in Bornean gingers (Zingiberaceae). These plants have strongly zygomorphic flowers pollinated by spiderhunter birds, bees of the genus Amegilla, and halictid bees. • METHODS: We identified pollination systems through field observations and recorded petal color, quantity of floral rewards, and seven measures of flower morphology in 28 ginger species. Phylogenetic trees were constructed from nucleotide sequences of the matK and ITS regions. We examined the correlations between the evolution of pollination systems and floral traits using phylogenetically independent contrasts. • KEY RESULTS: Significant association was found between pink color and spiderhunter pollination, orange and Amegilla pollination, and yellow and white and halictid pollination. Sugar production was higher in spiderhunter-pollinated species and lower in halictid-pollinated. Meanwhile, there was a significant association only for a subset of the floral morphological characters measured. Floral tube length, which is often thought to evolve to match the lengths of pollinator probing apparatuses, did not show any correlation. • CONCLUSIONS: There is considerable variation in the strength of association among pollination systems and floral traits. Lack of significant correlation in some traits could partly be explained by floral functions other than pollination, such as adaptations to prevent herbivore damage to the ovules. Further studies on these factors may improve understanding of plant-pollinator interactions.

A new pollination system: brood-site pollination by flower bugs in Macaranga (Euphorbiaceae).

BACKGROUND AND AIMS: Macaranga (Euphorbiaceae) is a large genus of dioecious trees with approx. 260 species. To date, only one pollination study of the genus has reported brood-site pollination by thrips in M. hullettii. In this study, the pollination system of Macaranga tanarius is reported. METHODS: The study was conducted on Okinawa and Amami Islands, Japan. Flower visitors on M. tanarius were collected and their pollen load and behaviour on the flowers examined, as well as inflorescence structure and reward for the pollinators. KEY RESULTS: The most abundant flower visitors found on the male and female inflorescences were Orius atratus (Anthocoridae, Hemiptera), followed by Decomioides schneirlai (Miridae, Hemiptera). Pollen load on O. atratus from flowering pistillate inflorescences was detected as well as from staminate flowers. Orius atratus and D. schneirlai are likely to use the enclosed chambers formed by floral bracts as breeding sites before and during flower anthesis, and feed on nectar on the adaxial surface of flower bracts. The extrafloral nectary has a ball-shaped structure and the contained nectar is not exposed; the hemipterans pierce the ball to suck out the nectar. CONCLUSIONS: The results indicate that the plant is pollinated by flower bugs breeding on the inflorescences. This study may be the first report of pollination systems in which flower bugs are the main pollinators. Similarity of pollination systems between M. hullettii and M. tanarius indicates that the two brood-site pollination systems have the same origin. The pollinator species belongs to a predacious group, whose major prey includes thrips. The pollination system might represent a unique example of evolution from predatory flower visitors feeding on the pollinators (thrips) to the main pollinators.

Irregular droughts trigger mass flowering in aseasonal tropical forests in asia.

General flowering is a community-wide masting phenomenon, which is thus far documented only in aseasonal tropical forests in Asia. Although the canopy and emergent layers of forests in this region are dominated by species of a single family, Dipterocarpaceae, general flowering involves various plant groups. Studying proximate factors and estimating the flowering patterns of the past and future may aid our understanding of the ecological significance and evolutionary factors behind this phenomenon. Here we show that this phenomenon is most likely triggered by irregular droughts based on 10 years of observations. In the aseasonal forests of SE Asia, droughts tend to occur during transition periods from La Niña to El Niño, which results in an irregular 6-7-yr cycle involving a dry period with several droughts and a wet period without droughts. The magnitude of a flowering event also depends on the timing of droughts associated with the El Niño southern oscillation (ENSO) cycle, with the largest events occurring after an interval of several years with no flowering. Because most plant species can only reproduce successfully during large flowering events, changes in the ENSO cycle resulting from global warming, may have serious ramifications for forest regeneration in this region.

A review of brood-site pollination mutualism: plants providing breeding sites for their pollinators.

In this paper, I review pollination systems in which plants provide breeding sites as a reward for pollination. I divide the pollinators into three groups based upon ovipositing sites and the larval food of insects. The first group consists of ovule parasites found in only five plant lineages, e.g., the fig wasps and yucca moths, pollination systems in which pollinator specificity is very high. The second group is pollen parasitism, primarily by thrips (Thysanoptera), but specificity of the pollinators is low. In the third group, pollinator larvae (Coleoptera and Diptera) develop in decomposed flowers and inflorescences of plants and these adaptations evolved repeatedly via different pathways in various plant taxa. Pollinator specificity varies, and shifts in pollinators may occur between related or unrelated insects.

Aristolochia spp. (Aristolochiaceae) pollinated by flies breeding on decomposing flowers in Panama.

This study presents breeding and pollination systems of Aristolochia maxima and A. inflata in a seasonal tropical forest of Panama. Aristolochia is the most diverse genus of Aristolochiaceae, with ∼120 species distributed throughout the tropics and subtropics. All the Aristolochia species studied so far are pollinated by saprophagous flies of different families, which are presumably deceived by floral odor. Flowers of many species have trap-and-release mechanisms. The flowers attract and imprison pollinators during the female stage first day of flowering and release them after anther dehiscence. Pollination systems of A. maxima and A. inflata are different from those of other Aristolochia in lacking trap mechanisms. Furthermore, the pollinators oviposit in the flowers, and their larvae grow on the fallen, decaying flowers on the ground. Therefore, the plants have a mutualistic relationship with their pollinators. Self-compatible A. inflata is pollinated by Megaselia sakaiae (Phoridae, Diptera). The pollinator may be specialized to Aristolochia flowers, which is the only substrate for larval development. On the other hand, self-incompatible A. maxima is pollinated by Drosophila spp. (Drosophilidae, Diptera), which utilize Aristolochia flowers as a breeding site only occasionally. This pollination mutualism might have evolved from deceit pollination.