Abstract: Tropical forests are biodiversity hotspots, but it is not well understood how this diversity is structured and maintained. One hypothesis rests on the generation of a range of metabolic niches, with varied composition, supporting a high species diversity. Characterizing soil metabolomes can reveal fine-scale differences in composition and potentially help explain variation across these habitats. In particular, little is known about canopy soils, which are unique habitats that are likely to be sources of additional biodiversity and biogeochemical cycling in tropical forests. We studied the effects of diverse tree species and epiphytes on soil metabolomic profiles of forest floor and canopy suspended soils in a French Guianese rainforest. We found that the metabolomic profiles of canopy suspended soils were distinct from those of forest floor soils, differing between epiphyte-associated and non-epiphyte suspended soils, and the metabolomic profiles of suspended soils varied with host tree species, regardless of association with epiphyte. Thus, tree species is a key driver of rainforest suspended soil metabolomics. We found greater abundance of metabolites in suspended soils, particularly in groups associated with plants, such as phenolic compounds, and with metabolic pathways related to amino acids, nucleotides, and energy metabolism, due to the greater relative proportion of tree and epiphyte organic material derived from litter and root exudates, indicating a strong legacy of parent biological material. Our study provides evidence for the role of tree and epiphyte species in canopy soil metabolomic composition and in maintaining the high levels of soil metabolome diversity in this tropical rainforest. It is likely that a wide array of canopy microsite-level environmental conditions, which reflect interactions between trees and epiphytes, increase the microscale diversity in suspended soil metabolomes

Abstract: The important fertilizing role of atmospheric dust, and particularly African dust, in tropical rainforests is increasingly recognized but still poorly quantified. To better evaluate dust input into the Caribbean basin, we sampled critical zone compartments of a small forested volcanic catchment in Guadeloupe (soils, parent rock, atmospheric dust, plants, soil solutions, stream and rain waters). The aims of this study are to track sources of cation nutrients (Ca, Mg, K, Sr) developed on highly weathered soil in the rainforest of Guadeloupe, to quantify plant recycling of these nutrients, and to identify constraints on regolith development and its associated nutrient pool. In the Quiock Creek catchment, a large isotopic range of 87Sr/86Sr and eNd values was observed despite the small scale of observation. Sr isotopic composition of the dissolved load varied from 0.7084 in rainfall to 0.7110 in soil solution, whereas it ranges between 0.7068 and 0.7153 for soil samples and between 0.7096 and 0.7102 for plants. The Nd isotopic composition varied between -8.39 in near-surface soil samples to 2.71 in deeper soil. All samples had an intermediate signature between that of the bedrock endmember (87Sr/86Sr = 0.7038; eNd = 4.8) and the atmospheric endmember (sea salt: 87Sr/86Sr = 0.7092 and Saharan dust: 87Sr/86Sr = 0.7187, eNd=-11.5). The regolith was built on pyroclastic deposits, but, because of extreme leaching, the regolith has lost its original bedrock signature and inherited an exogenous atmospheric signature. Our results show that only the chemical weathering of the fresh near-surface minerals can provide nutrients to the ecosystem (first 30 cm). However, this dust weathering is too low to sustain the tropical forest ecosystem on its own. The cationic mass balance at the catchment scale, as well as the Sr isotopic signature, show that cation and Sr fluxes are of atmospheric origin only and that original bedrock no longer participates in nutrient cycles. The vegetation reflects the 87Sr/86Sr of the dissolved pool of atmospheric Sr. At the soil-plant scale, the cation-nutrient fluxes provided by vegetation (litter fall + leaf excretion) are major compared to input and output fluxes. The annual Ca, K, Sr and Mg fluxes within the vegetation are, respectively, 31, 28, 20 and 3 times greater than the exported fluxes at the outlet of the basin. The residence time of nutrients in the vegetation is 16 years for K and close to 45 years for Sr, Ca and Mg. These results emphasize the highly efficient vegetative turnover that dominates the nutrient cycle in the Quiock Creek catchment. This first characterization of biogeochemical cycles in the Guadeloupean rainforest suggests that the forest community of Quiock Creek is sustained by a small near-surface nutrient pool disconnected from the deep volcanic bedrock. We also demonstrated that, even with efficient nutrient recycling, Saharan dust plays a significant role in maintaining ecosystem productivity in Guadeloupe over long-time scales.

Abstract: Food robbing, or cleptobiosis, has been well documented throughout the animal kingdom. For insects, intrafamilial food robbing is known among ants, but social wasps (Vespidae; Polistinae) taking food from ants has, to the best of our knowledge, never been reported. In this paper, we present two cases involving social wasps robbing food from ants associated with myrmecophytes. (1) Polybioides tabida F. (Ropalidiini) rob pieces of prey from Tetraponera aethiops Smith (Formicidae; Pseudomyrmecinae) specifically associated with Barteria fistulosa Mast. (Passifloraceae). (2) Charterginus spp. (Epiponini) rob food bodies from myrmecophytic Cecropia (Cecropiaceae) exploited by their Azteca mutualists (Formicidae; Dolichoderinae) or by opportunistic ants (that also attack cleptobiotic wasps). We note here that wasps gather food bodies (1) when ants are not yet active; (2) when ants are active, but avoiding any contact with them by flying off when attacked; and (3) through the coordinated efforts of two to five wasps, wherein one of them prevents the ants from leaving their nest, while the other wasps freely gather the food bodies. We suggest that these interactions are more common than previously thought.

Abstract: Theory suggests that spatial structuring should select for intermediate levels of virulence in parasites, but empirical tests are rare and have never been conducted with castration (sterilizing) parasites. To test this theory in a natural landscape, we construct a spatially explicit model of the symbiosis between the ant-plant Cordia nodosa and its two, protecting ant symbionts, Allomerus and Azteca. Allomerus is also a castration parasite, preventing fruiting to increase colony fecundity. Limiting the dispersal of Allomerus and host plant selects for intermediate castration virulence. Increasing the frequency of the mutualist, Azteca, selects for higher castration virulence in Allomerus, because seeds from Azteca-inhabited plants are a public good that Allomerus exploits. These results are consistent with field observations and, to our knowledge, provide the first empirical evidence supporting the hypothesis that spatial structure can reduce castration virulence and the first such evidence in a natural landscape for either mortality or castration virulence.

Abstract: Drier periods from the late Pleistocene and early Holocene have been hypothesized to have caused the disappearance of various rainforest species over large geographical areas in South America and restricted the extant populations to mesic sites. Subsequent improvement in climatic conditions has been associated with recolonization. Changes in population size associated with these extinction-recolonization events should have affected genetic diversity within species. However, these historical hypotheses and their genetic consequences have rarely been tested in South America. Here, we examine the diversity of the chloroplast and nuclear genomes in a Neotropical rainforest tree species, Vouacapoua americana (Leguminosae, Caesalpinioideae) in French Guiana. The chloroplast diversity was analyzed using a polymerase chain reaction-restriction fragment length polymorphism method (six pairs of primers) in 29 populations distributed over most of French Guiana, and a subset of 17 populations was also analyzed at nine polymorphic microsatellite loci. To determine whether this species has experienced extinction-recolonization, we sampled populations in areas supposedly not or only slightly affected by climatic changes, where the populations would not have experienced frequent extinction, and in areas that appear to have been recently recolonized. In the putatively recolonized areas, we found patches of several thousands of hectares homogeneous for chloroplast variation that can be interpreted as the effect of recolonization processes from several geographical origins. In addition, we observed that, for both chloroplast and nuclear genomes, the populations in newly recolonized areas exhibited a significantly smaller allelic richness than others. Controlling for geographic distance, we also detected a significant correlation between chloroplast and nuclear population differentiation. This result indicates a cytonuclear disequilibrium that can be interpreted as a historical signal of a genetic divergence between fragmented populations. In conclusion, the spatial genetic structure of contemporary V. americana populations shows evidence that this species has experienced large extinction-recolonization events, which were possibly caused by past climatic change.