Asian Tropical Rainforest Research Articles

The Origin of Evergreen Broad-Leaved Forests in East Asia from the Evidence of Floristic Elements.

Arguments about the origin and evolution of the evergreen broad-leaved forests in East Asia exist generally, and are even contradictory in some cases. The origin and evolution of the flora of East Asia, especially in the evolutionary process, the formation time of the Asian monsoon, the implications of phylogenetic and biogeographic studies on some important taxa, and the implications of palaeobotanical evidence are debatable. Most research from different disciplines suggests that the monsoon in the Miocene was key to the diversification of East Asian flora and its evergreen broad-leaved forests. The common view is that the evergreen broad-leaved forests of East Asia are closely related to the monsoon's intensity and developments, which were caused by the uplift of Himalaya-Tibet during or after the mid-Miocene. Analysis of the floristic elements show that the present subtropical evergreen broad-leaved forests in East Asia could have an early or ancient tropical origin and a tropical Asian affinity, but that their species are dominated by endemic Chinese or East Asian ones, many of which have tropical Asian affinity or are tropical sister species. The time of Himalayan uplift and the intensity of the monsoon climate are believed to be key to the formation of the evergreen broad-leaved forests in East Asia. Combined with existing paleobotanical findings, the uplift of the Himalayas and the formation of the monsoon climate, as well as floristic elements of the subtropical evergreen broad-leaved forests, we believe that they evolved from an Asian tropical rainforest after the mid-Miocene in the southeastern region of East Asia, while the ancient subtropical evergreen broad-leaved forests in the southwestern region continuously evolved into the present subtropical ones.

Exploring Adaptive Phenotypes for the Human Calcium-Sensing Receptor Polymorphism R990G.

Rainforest hunter-gatherers from Southeast Asia are characterized by specific morphological features including a particularly dark skin color (D), short stature (S), woolly hair (W), and the presence of steatopygia (S)-fat accumulation localized in the hips (DSWS phenotype). Based on previous evidence in the Andamanese population, we first characterized signatures of adaptive natural selection around the calcium-sensing receptor gene in Southeast Asian rainforest groups presenting the DSWS phenotype and identified the R990G substitution (rs1042636) as a putative adaptive variant for experimental follow-up. Although the calcium-sensing receptor has a critical role in calcium homeostasis by directly regulating the parathyroid hormone secretion, it is expressed in different tissues and has been described to be involved in many biological functions. Previous works have also characterized the R990G substitution as an activating polymorphism of the calcium-sensing receptor associated with hypocalcemia. Therefore, we generated a knock-in mouse for this substitution and investigated organismal phenotypes that could have become adaptive in rainforest hunter-gatherers from Southeast Asia. Interestingly, we found that mouse homozygous for the derived allele show not only lower serum calcium concentration but also greater body weight and fat accumulation, probably because of enhanced preadipocyte differentiation and lipolysis impairment resulting from the calcium-sensing receptor activation mediated by R990G. We speculate that such differential features in humans could have facilitated the survival of hunter-gatherer groups during periods of nutritional stress in the challenging conditions of the Southeast Asian tropical rainforests.

Lianas shift towards larger sizes and more acquisitive trait values in an Asian tropical rainforest

AbstractGlobal change is impacting forests worldwide, leading to shifts in forest dynamics and functional composition. We evaluated the changes in the liana community and trait composition over a five‐year period (2014–2019) in a Chinese tropical rainforest and assessed the underlying putative mechanisms. We monitored >20,000 lianas in a 20‐ha plot, and analyzed community changes for each of the 20 1‐ha plots. To identify the putative drivers underlying community change, we used community‐weighted mean (CWM) trait values of 18 functional traits that are important for liana performance. During the 5‐year period, liana density decreased by 12.6% because of the high mortality of small lianas, whereas liana basal area increased by 5.8% because of the high growth of large lianas. After 5 years, liana communities showed a shift in trait values indicating that they changed towards more large, acquisitive lianas with rapid water use. The temporal shift from slow to fast community trait spectra in carbon, nutrient, and water use was also supported by shifts in the individual CWM traits, from conservative tough leaves towards more acquisitive and water‐spending leaves with higher K concentration, leaf thickness, and vessel diameter. Overall, we found no support for a role of disturbances or drought as drivers of the observed changes in the studied liana community. Instead, our study implies that CO2 fertilization should be considered to better understand dynamics in liana communities in tropical forests.Abstract in Chinese is available with online material.

An ecological transcriptome approach to capture the molecular and physiological mechanisms of mass flowering in Shorea curtisii.

Climatic factors have commonly been attributed as the trigger of general flowering, a unique community-level mass flowering phenomenon involving most dipterocarp species that forms the foundation of Southeast Asian tropical rainforests. This intriguing flowering event is often succeeded by mast fruiting, which provides a temporary yet substantial burst of food resources for animals, particularly frugivores. However, the physiological mechanism that triggers general flowering, particularly in dipterocarp species, is not well understood largely due to its irregular and unpredictable occurrences in the tall and dense forests. To shed light on this mechanism, we employed ecological transcriptomic analyses on an RNA-seq dataset of a general flowering species, Shorea curtisii (Dipterocarpaceae), sequenced from leaves and buds collected at multiple vegetative and flowering phenological stages. We assembled 64,219 unigenes from the transcriptome of which 1,730 and 3,559 were differentially expressed in the leaf and the bud, respectively. Differentially expressed unigene clusters were found to be enriched with homologs of Arabidopsis thaliana genes associated with response to biotic and abiotic stresses, nutrient level, and hormonal treatments. When combined with rainfall data, our transcriptome data reveals that the trees were responding to a brief period of drought prior to the elevated expression of key floral promoters and followed by differential expression of unigenes that indicates physiological changes associated with the transition from vegetative to reproductive stages. Our study is timely for a representative general flowering dipterocarp species that occurs in forests that are under the constant threat of deforestation and climate change as it pinpoints important climate sensitive and flowering-related homologs and offers a glimpse into the cascade of gene expression before and after the onset of floral initiation.

El Niño-Southern Oscillation forcing on carbon and water cycling in a Bornean tropical rainforest

Carbon dioxide and water vapor exchanges between tropical forest canopies and the atmosphere through photosynthesis, respiration, and evapotranspiration (ET) influence carbon and water cycling at the regional and global scales. Their inter- and intra-annual variations are sensitive to seasonal rhythms and longer-timescale tropical climatic events. In the present study, we assessed the El Niño-Southern Oscillation (ENSO) influence on ET and on the net ecosystem exchange (NEE), using eddy-covariance flux observations in a Bornean rainforest over a 10-y period (2010-2019) that included several El Niño and La Niña events. From flux model inversions, we inferred ecophysiological properties, notably the canopy stomatal conductance and "big-leaf" maximum carboxylation rate (Vcmax25_BL). Mean ET values were similar between ENSO phases (El Niño, La Niña, and neutral conditions). Conversely, the mean net ecosystem productivity was highest during La Niña events and lowest during El Niño events. Combining Shapley additive explanation calculations for nine controlling factors with a machine-learning algorithm, we determined that the primary factors for ET and NEE in the La Niña and neutral phases were incoming shortwave solar radiation and Vcmax25_BL, respectively, but that canopy stomatal conductance was the most significant factor for both ET and NEE in the El Niño phase. A combined stomatal-photosynthesis model approach further indicated that Vcmax25_BL differences between ENSO phases were the most significant controlling factor for canopy photosynthesis, emphasizing the strong need to account for ENSO-induced ecophysiological factor variations in model projections of the long-term carbon balance in Southeast Asian tropical rainforests.

The genetic structuring in pollinating wasps of Ficus hispida in continental Asia.

The interaction between figs and fig wasps provides a striking example of obligate brood site pollination mutualism. Monoecious figs, constituting independent radiations in each tropical biome, are present in significant proportions worldwide, but in continental Asia, dioecious figs have diverged into various niches, making the region's assemblage remarkably diverse. However, the reproductive success of figs and fig wasps largely depends on the fig wasp dispersal process. Monoecious fig pollinators in continental Asian tropical rain forests exhibit high gene flow of the plant, while many dioecious fig pollinators have a more restricted gene flow. However, there are limited studies on the genetic structure of dioecious Ficus pollinators that pollinate figs with intermediate gene flow. Here, we used molecular methods to investigate the genetic structure of pollinating wasps of the widely distributed dioecious Ficus hispida in China and Southeast Asia. Sequence data from two gene regions were used: the mitochondrial protein-coding gene cytochrome c oxidase subunit I (COI) and the nuclear 28S genes. Both molecular and morphological results support two fig wasp species at our sampling sites. Our findings suggest that for widely sympatric Ficus species in continental Asia, monoecious figs presenting long gene glow have the fewest fig wasp species, followed by dioecious figs presenting intermediate gene flow, and dioecious figs presenting local gene flow have the most fig wasp species.

Abiotic and biotic drivers of liana community change in an Asian tropical rainforest

Lianas have a major influence on community and ecosystem processes in tropical forests, but their dynamics and underlying drivers have rarely been assessed. This study evaluates which demographic processes underlie liana community change and how these demographic processes are driven by abiotic factors (light gaps, soil nutrients, soil water availability, and topography), and biotic factors such as competition by life forms (liana and tree basal area) and the functional properties of the liana community. In a tropical rainforest in Southwest China > 20,000 liana individuals were monitored in 20 1-ha plots and for each plot, average trait values of the liana community were determined for eighteen functional traits that are important for plant performance. Across the 20 plots, changes in liana density were more strongly driven by mortality than by recruitment. Liana recruitment and mortality were driven by biotic factors, especially the functional properties. Liana mortality was higher for acquisitive communities, possibly because of strong competition amongst fast-growing liana species and the short lifespan of pioneers. Liana growth was driven by abiotic factors and increased with elevation and soil water availability. Hence, liana community dynamics are shaped by mortality, and functional properties are more important than the environment. Simultaneously testing the roles of multiple environmental factors and inherent plant characteristics yields better insights into the mechanisms underlying community dynamics.

High vapour pressure deficit enhances turgor limitation of stem growth in an Asian tropical rainforest tree.

Tropical forests are experiencing increases in vapour pressure deficit (D), with possible negative impacts on tree growth. Tree-growth reduction due to rising D is commonly attributed to carbon limitation, thus overlooking the potentially important mechanism of D-induced impairment of wood formation due to an increase in turgor limitation. Here we calibrate a mechanistic tree-growth model to simulate turgor limitation of radial stem growth in mature Toona cilitata trees in an Asian tropical forest. Hourly sap flow and dendrometer measurements were collected to simulate turgor-driven growth during the growing season. Simulated seasonal patterns of radial stem growth matched well with growth observations. Growth mainly occurred at night and its pre-dawn build-up appeared to be limited under higher D. Across seasons, the night-time turgor pressure required for growth was negatively related to previous midday D, possibly due to a relatively high canopy conductance at high D, relative to stem rehydration. These findings provide the first evidence that tropical trees grow at night and that turgor pressure limits tree growth. We suggest including turgor limitation of tree stem growth in models also for tropical forest carbon dynamics, in particular, if these models simulate effects of warming and increased frequency of droughts.

Characterization of Leaf Transcriptome in a Tropical Tree Species, <i>Shorea curtisii</i>, over a Flowering Season

General flowering (GF) is a synchronous flowering phenomenon in the Southeast Asian tropical rainforests that occurs at irregular intervals of multiple years. While in this study, the leaf transcriptome of a GF species, Shorea curtisii obtained from three-time points – before and after floral initiation, and post-flowering stage – was sequenced, the unpredictable intervals of GF raise conservation concerns for these under-researched forests with rich economically and ecologically important species. We assembled 243,759,478 sequencing reads into 39,943 non-redundant unigenes including 677 putative homologs of Arabidopsis thaliana flowering-related genes. Differential expression analysis conducted on pairwise comparisons of the time points identified 930 differentially expressed unigenes, which includes 17 flowering-related homologs. The differential expression of unigenes with significant enrichments of functions related to drought corroborated the involvement of drought as an environmental cue for GF, with the outcomes of this study offering an insight into the conservation of floral regulatory genes and pathways in Shorea and possibly being used as a model to better understand the floral initiation cues and regulation of GF trees.

Strategies for the discovery of potential anticancer agents from plants collected from Southeast Asian tropical rainforests as a case study.

Covering up to early 2023The present review summarizes recent accomplishments made as part of a multidisciplinary, multi-institutional anticancer drug discovery project, wherein samples comprising higher plants were collected primarily from Southeast Asia, and also from Central America, and the West Indies. In the introductory paragraphs, a short perspective is provided on the current importance of plants in the discovery of cancer therapeutic agents, and the contributions of other groups working towards this objective are mentioned. For our own investigations, following their collection, tropical plants have been subjected to solvent extraction and biological evaluation for their antitumor potential. Several examples of purified plant lead bioactive compounds were obtained and characterized, and found to exhibit diverse structures, including those of the alkaloid, cardiac glycoside, coumarin, cucurbitacin, cyclobenzofuran (rocaglate), flavonoid, lignan, and terpenoid types. In order to maximize the efficiency of work on drug discovery from tropical plant species, strategies to optimize various research components have been developed, including those for the plant collections and taxonomic identification, in accordance with the requirements of contemporary international treaties and with a focus on species conservation. A major component of this aspect of the work is the development of collaborative research agreements with representatives of the source countries of tropical rainforest plants. The phytochemical aspects have included the preparation of plant extracts for initial screening and the selection of promising extracts for activity-guided fractionation. In an attempt to facilitate this process, a TOCSY-based NMR procedure has been applied for the determination of bioactive rocaglate derivatives in samples of Aglaia species (Meliaceae) collected for the project. Preliminary in vitro and in vivo mechanistic studies carried out by the authors are described for two tropical plant-derived bioactive lead compounds, corchorusoside C and (+)-betulin, including work conducted with a zebrafish (Danio rerio) model. In the concluding remarks, a number of lessons are summarized that our group has learned as a result of working on anticancer drug discovery using tropical plants, which we hope will be of interest to future workers.

Host species and habitats shape the bacterial community of gut microbiota of three non-human primates: Siamangs, white-handed gibbons, and Bornean orangutans.

The gut microbiome is essential for a host to digest food, maintain health, and adapt to environments. Bacterial communities of gut microbiota are influenced by diverse factors including host physiology and the environment. Many non-human primates (NHPs), which are physiologically close to humans, are in danger of extinction. In this study, the community structure of the gut microbiota in three NHPs: siamangs (Symphalangus syndactylus, Ss), Bornean orangutans (Pongo pygmaeus, Pp), and white-handed gibbons (Hylobates lar, Hl)—housed at the largest Zoo in Taiwan were analyzed. Pp and Ss were housed in the Asian tropical rainforest area, while Hl was housed in two separate areas, the Asian tropical rainforest area and the conservation area. Bacterial community diversity of Ss, indicated by the Shannon index, was significantly higher compared with that of Hl and Pp, while the richness (Chao 1) and observed operational taxonomic units (OTUs) were similar across the three species of NHPs. Host species was the dominant factor shaping the gut microbial community structure. Beta-diversity analysis including non-metric multidimensional scaling (NMDS) and unweighted pair group method with arithmetic mean (UPGMA) suggested gut bacterial communities of Hl housed in the conservation area were closely related to each other, while the bacterial communities of Hl in the rainforest area were dispersedly positioned. Further analysis revealed significantly higher abundances of Lactobacillus fermentum, L. murinus, and an unclassified species of Lactobacillus, and a lower abundance of Escherichia-Shigella in Hl from the conservation area relative to the rainforest area. The ratio of Lactobacillus to Escherichia-Shigella was 489.35 and 0.013 in Hl inhabiting the conservation and rainforest areas, respectively. High abundances of Lactobacillus and Bifidobacterium and a high ratio of Lactobacillus to Escherichia-Shigella were also observed in one siamang with notable longevity of 53 years. Data from the study reveal that host species acted as the fundamental driving factor in modulating the community structure of gut microbiota, but that habitats also acted as key determinants within species. The presence and high abundance of probiotics, such as Bifidobacterium and Lactobacillus, provide potential indicators for future diet and habitat optimization for NHPs, especially in zoological settings.

Evidence in stable isotope ratios for lichen‐feeding by Lithosiini moths from a tropical rainforest but not from a temperate forest

AbstractLithosiini (Lepidoptera: Erebidae: Arctiinae) is distinctive in having some species that feed on lichens, whereas the majority of moths feed on vascular plants. However, the larval diet of most Lithosiini species is poorly known. This study examines whether Lithosiini species, collected in a tropical rainforest of Borneo (nine species) and a temperate forest of Japan (eight species), feed on lichens as larvae, based on stable isotope analyses. As a result, the δ15N values for eight of nine Lithosiini species collected from Borneo were notably lower than those of nine co‐occurring herbivorous non‐Lithosiini species, and were similar to those of sympatric, lichen‐feeding termites; however, δ13C and δ15N values of one Lithosiini species (Adites sp.) were significantly higher than those of the other moth species and similar to those of humus‐feeding termites and predatory insects occurring at the same site. These results have suggested that the Lithosiini in the Southeast Asian tropical rainforests contain some species that feed on lichens as their larval main diet and at least one species whose larvae feed on humus or animal‐derived materials. In contrast, the δ13C and δ15N values of all examined Lithosiini species (eight species) in the temperate forest have suggested that their larvae fed on plants and not on lichens. Our stable isotope ratio analysis presented quantitative evidence suggesting lichen‐feeding by Lithosiini moths in a tropical rainforest without observation of feeding behavior during the larval stages.

Energy Balance Closure Problem over a Tropical Seasonal Rainforest in Xishuangbanna, Southwest China: Role of Latent Heat Flux

The unresolved energy-unclosed problem in micrometeorology refers to the fact that the sum of turbulent fluxes (sensible and latent heat fluxes, Hs and LE) monitored by eddy covariance (EC) methods tends to be lower than the available energy (net radiation (Rn), soil heat flux (G), and heat storage (S)). The lack of energy balance closure (EBC) increases evapotranspiration-measurement uncertainty. Using EC data from Xishuangbanna, a Southeast Asian tropical seasonal rainforest, we analyzed the energy distribution and closure based on micrometeorological features. We found that: (1) the EBC in the rainy season exceeds that in other seasons and that the seasonal moisture content, frictional wind velocity (u*), and LE contribute to the high seasonal variability in EBC; (2) the annual closure is approximately 65%, and energy non-closure is influenced by turbulence intensity and atmospheric stability. When the atmospheric state is unstable to near neutral, u* is greatest, and EBC can reach nearly 80%. (3) energy is mainly allocated to LE, and energy non-closure leads to LE underestimation, especially in the foggy-cool and hot-dry seasons. (4) Heat storage and large time-scale flux effects on EBC were excluded. The causes of energy non-closure in the tropical calm zone need further investigation.

Effects of Nitrogen Additions on Soil Respiration in an Asian Tropical Montane Rainforest

Understanding the impacts of nitrogen (N) addition on soil respiration (RS) and its temperature sensitivity (Q10) in tropical forests is very important for the global carbon cycle in a changing environment. Here, we investigated how RS respond to N addition in a tropical montane rainforest in Southern China. Four levels of N treatments (0, 25, 50, and 100 kg N ha−1 a−1 as control (CK), low N (N25), moderate N (N50), and high N (N100), respectively) were established in September 2010. Based on a static chamber-gas chromatography method, RS was measured from January 2015 to December 2018. RS exhibited significant seasonal variability, with low RS rates appeared in the dry season and high rates appeared in the wet season regardless of treatment. RS was significantly related to the measured soil temperature and moisture. Our results showed that soil RS increased after N additions, the mean annual RS was 7% higher in N25 plots, 8% higher in N50 plots, and 11% higher in N100 plots than that in the CK plots. However, the overall impacts of N additions on RS were statistically insignificant. For the entire study period, the CK, N25, N50, and N100 treatments yielded Q10 values of 2.27, 3.45, 4.11, and 2.94, respectively. N addition increased the temperature sensitivity (Q10) of RS. Our results suggest that increasing atmospheric N deposition may have a large impact on the stimulation of soil CO2 emissions from tropical rainforests in China.

Effects of vegetation structure on avian biodiversity in a selectively logged hill dipterocarp forest

Southeast Asian tropical rainforests are shrinking at an alarming rate largely due to anthropogenic activities such as logging and agricultural expansion. The loss of tropical rainforests from human exploitations caused devastating and irreversible impacts on avian biodiversity. The establishment of protected areas is an effective tool to mitigate further forest biodiversity loss. However, the ability of degraded rainforest to support avian biodiversity is still remain little known. Here, we assessed bird assemblages in a hill dipterocarp forest in Peninsular Malaysia which was selectively logged almost three decades ago. We examined the effects of site-level attributes, particularly vegetation structure on bird community composition, species richness and abundance of selected feeding guild groups (i.e. insectivorous, carnivorous, and frugivorous). Generally, we found that a selectively logged hill dipterocarp forest can still support a large proportion of forest birds, including those species with high conservation values. Our data also revealed that avian biodiversity was positively related to the number of fallen snags, number of standing snags, number of shrubs, number of trees with DBH < 5 cm, and elevation. In contrast, avian biodiversity was negatively linked to canopy cover percentage, number of palms, and number of trees with DBH 30–50 cm. Our findings suggest the importance of post-harvest site-level attributes management in order to improve avian biodiversity in logged hill dipterocarp forests. Above all, urgent actions are needed to incorporate hill dipterocarp forests, including those already disturbed by logging into protected area networks in Peninsular Malaysia to mitigate forest biodiversity loss.

Size dependent associations between tree diameter growth rates and functional traits in an Asian tropical seasonal rainforest.

Many studies focus on the relationships between plant functional traits and tree growth performances. However, little is known about the ontogenetic shifts of the relationships between functional traits and tree growth. This study examined associations between stem and leaf functional traits and growth rates and their ontogenetic shifts across 20 tropical tree species in a tropical seasonal rainforest in Xishuangbanna, south-west China. For each species, physiological active branches of individual trees belonged to three size classes (i.e. small, diameter at breast height (DBH) 5-10 cm; middle, DBH 10-20 cm; big, DBH >20 cm) were sampled respectively. We measured 18 morphological and structural traits, which characterised plant hydraulic properties or leaf economic spectrum. Associations between diameter growth rates and functional traits were analysed across three size classes. Our results revealed that diameter growth rates of big-sized trees were mainly related to traits related to plant hydraulic efficiency (i.e. theoretical hydraulic conductivity (Ktheo) and leaf vein density (Dvein)), which suggests that the growth of large trees is limited mainly by their xylem water transport capacity. For middle-sized trees, growth rates were significantly related to traits representing leaf economic spectrum (i.e. specific leaf area (SLA), individual leaf mass (ILM), palisade thickness (PT) and spongy thickness (SP)). Diameter growth rates of small-sized trees were not correlated with hydraulic or leaf economic traits. Thus, the associations between tree growth rates and functional traits are size dependent. Our results suggest ontogenetic shift of functional traits which could potential contribute to different growth response to climate change.

Forest aboveground biomass stock and resilience in a tropical landscape of Thailand

Abstract. Half of Asian tropical forests were disturbed in the last century resulting in the dominance of secondary forests in Southeast Asia. However, the rate at which biomass accumulates during the recovery process in these forests is poorly understood. We studied a forest landscape located in Khao Yai National Park (Thailand) that experienced strong disturbances in the last century due to clearance by swidden farmers. Combining recent field and airborne laser scanning (ALS) data, we first built a high-resolution aboveground biomass (AGB) map of over 60 km2 of forest landscape. We then used the random forest algorithm and Landsat time series (LTS) data to classify landscape patches as non-forested versus forested on an almost annual basis from 1972 to 2017. The resulting chronosequence was then used in combination with the AGB map to estimate forest carbon recovery rates in secondary forest patches during the first 42 years of succession. The ALS-AGB model predicted AGB with an error of 14 % at 0.5 ha resolution (RMSE=45 Mg ha−1) using the mean top-of-canopy height as a single predictor. The mean AGB over the landscape was 291 Mg ha−1, showing a high level of carbon storage despite past disturbance history. We found that AGB recovery varies non-linearly in the first 42 years of the succession, with an increasing rate of accumulation through time. We predicted a mean AGB recovery rate of 6.9 Mgha-1yr-1, with a mean AGB gain of 143 and 273 Mg ha−1 after 20 and 40 years, respectively. This rate estimate is about 50 % larger than the rate prescribed for young secondary Asian tropical rainforests in the 2019 refinement of the 2006 IPCC guidelines for national greenhouse gas inventories. Our study hence suggests that the new IPCC rates, which were based on limited data from Asian tropical rainforests, strongly underestimate the carbon potential of forest regrowth in tropical Asia. Our recovery estimates are also within the range of those reported for the well-studied Latin American secondary forests under similar climatic conditions. This study illustrates the potential of ALS data not only for scaling up field AGB measurements but also for predicting AGB recovery dynamics when combined with long-term satellite data. It also illustrates that tropical forest landscapes that were disturbed in the past are of utmost importance for the regional carbon budget and thus for implementing international programs such as REDD+.

Age constraints on a Neogene tropical rainforest in China and its relation to the Middle Miocene Climatic Optimum

Tropical rainforests have strongly influenced Earth systems throughout their evolutionary history. Plant taxa found in the Fotan Group of Fujian Province indicate that an Asian tropical rainforest prevailed in southeastern China during the Miocene. Abundant insect-bearing ambers co-occur with diagnostic plant fossils in outcrop. Fotan Group fossils demonstrate that highly diverse tropical ecosystems existed during the early Neogene in southeastern China. This study reports a robust 40Ar/39Ar age of 14.7 ± 0.4 Ma for the Fotan fossils. This age constrains interpretations of 1) when tropical rainforest ecosystems developed in China, 2) whether the Fotan flora temporally overlapped with the Asian tropical forest in India, and 3) whether the Middle Miocene Climatic Optimum triggered expansion of tropical rainforests in Asia. A precise age for Fotan units provides important constraints on the biogeographic history of the field area and paleographic models linking Asian and Indian biota.

Polygenic adaptation and convergent evolution on growth and cardiac genetic pathways in African and Asian rainforest hunter-gatherers

Different human populations facing similar environmental challenges have sometimes evolved convergent biological adaptations, for example, hypoxia resistance at high altitudes and depigmented skin in northern latitudes on separate continents. The "pygmy" phenotype (small adult body size), characteristic of hunter-gatherer populations inhabiting both African and Asian tropical rainforests, is often highlighted as another case of convergent adaptation in humans. However, the degree to which phenotypic convergence in this polygenic trait is due to convergent versus population-specific genetic changes is unknown. To address this question, we analyzed high-coverage sequence data from the protein-coding portion of the genomes of two pairs of populations: Batwa rainforest hunter-gatherers and neighboring Bakiga agriculturalists from Uganda and Andamanese rainforest hunter-gatherers and Brahmin agriculturalists from India. We observed signatures of convergent positive selection between the rainforest hunter-gatherers across the set of genes with "growth factor binding" functions ([Formula: see text]). Unexpectedly, for the rainforest groups, we also observed convergent and population-specific signatures of positive selection in pathways related to cardiac development (e.g., "cardiac muscle tissue development"; [Formula: see text]). We hypothesize that the growth hormone subresponsiveness likely underlying the adult small body-size phenotype may have led to compensatory changes in cardiac pathways, in which this hormone also plays an essential role. Importantly, in the agriculturalist populations, we did not observe similar patterns of positive selection on sets of genes associated with growth or cardiac development, indicating our results most likely reflect a history of convergent adaptation to the similar ecology of rainforests rather than a more general evolutionary pattern.

Breeding Biology of Great HornbillBuceros bicornisin Tropical Rainforest and Human-Modified Plantation Landscape in Western Ghats, India

Loss of mature tropical forests to agricultural expansion often creates landscapes with forest fragments embedded within a matrix of human-modified habitats and land uses. Such habitat fragmentation may be detrimental to species with specialized habitat and foraging requirements and their ability to persist in such landscapes may depend on their adaptability to habitat modification. Great Hornbills Buceros bicornis, among the largest birds in Asian tropical rainforests, depend on large trees for nesting and a diverse array of patchily distributed fruiting trees. In the human-modified landscape of the Anamalai Hills, India, we compared the breeding biology and nesting behaviour of Great Hornbills in contiguous rainforest (N=3 nests) and in modified habitat consisting of coffee plantations and rainforest fragments (N=5 nests). The nesting cycle of seven of the eight nests monitored varied between 114 and 130 days. Nest provisioning behaviour was similar in contiguous forest and modified habitat in terms of visitation and food delivery rates, but visitation tended to be higher and food delivery rate lower during the nestling phase than during incubation. As expected, tree density and native food plant diversity were lower in modified habitat than in continuous forest. The diversity of food provisioned was lower in modified habitat with a 57.5% dietary overlap with contiguous forest. Hornbills in the modified habitat of coffee plantations used non-native tree species for nesting and foraging, indicating their adaptability to modified landscapes.