Paralyzing Action from a Distance in an Arboreal African Ant Species

Due to their prowess in interspecific competition and ability to catch a wide range of arthropod prey (mostly termites with which they are engaged in an evolutionary arms race), ants are recognized as a good model for studying the chemicals involved in defensive and predatory behaviors. Ants' wide diversity of nesting habits and relationships with plants and prey types implies that these chemicals are also very diverse. Using the African myrmicine ant Crematogaster striatula as our focal species, we adopted a three-pronged research approach. We studied the aggressive and predatory behaviors of the ant workers, conducted bioassays on the effect of their Dufour gland contents on termites, and analyzed these contents. (1) The workers defend themselves or eliminate termites by orienting their abdominal tip toward the opponent, stinger protruded. The chemicals emitted, apparently volatile, trigger the recruitment of nestmates situated in the vicinity and act without the stinger having to come into direct contact with the opponent. Whereas alien ants competing with C. striatula for sugary food sources are repelled by this behavior and retreat further and further away, termites defend their nest whatever the danger. They face down C. striatula workers and end up by rolling onto their backs, their legs batting the air. (2) The bioassays showed that the toxicity of the Dufour gland contents acts in a time-dependent manner, leading to the irreversible paralysis, and, ultimately, death of the termites. (3) Gas chromatography-mass spectrometry analyses showed that the Dufour gland contains a mixture of mono- or polyunsaturated long-chain derivatives, bearing functional groups like oxo-alcohols or oxo-acetates. Electrospray ionization-mass spectrometry showed the presence of a molecule of 1584 Da that might be a large, acetylated alkaloid capable of splitting into smaller molecules that could be responsible for the final degree of venom toxicity

Coordinated community structure among trees, fungi and invertebrate groups in Amazonian rainforests

Little is known regarding how trophic interactions shape community assembly in tropical forests. Here we assess multi-taxonomic community assembly rules using a rare standardized coordinated inventory comprising exhaustive surveys of five highly-diverse taxonomic groups exerting key ecological functions: trees, fungi, earthworms, ants and spiders. We sampled 36 1.9-ha plots from four remote locations in French Guiana including precise soil measurements, and we tested whether species turnover was coordinated among groups across geographic and edaphic gradients. All species group pairs exhibited significant compositional associations that were independent from soil conditions. For some of the pairs, associations were also partly explained by soil properties, especially soil phosphorus availability. Our study provides evidence for coordinated turnover among taxonomic groups beyond simple relationships with environmental factors, thereby refining our understanding regarding the nature of interactions occurring among these ecologically important groups

Decay of similarity across tropical forest communities : integrating spatial distance with soil nutrients

Altres ajuts: Acord transformatiu CRUE-CSICUnderstanding the mechanisms that drive the change of biotic assemblages over space and time is the main quest of community ecology. Assessing the relative importance of dispersal and environmental species selection in a range of organismic sizes and motilities has been a fruitful strategy. A consensus for whether spatial and environmental distances operate similarly across spatial scales and taxa, however, has yet to emerge. We used censuses of four major groups of organisms (soil bacteria, fungi, ground insects, and trees) at two observation scales (1-m sampling point vs. 2,500-m plots) in a topographically standardized sampling design replicated in two tropical rainforests with contrasting relationships between spatial distance and nutrient availability. We modeled the decay of assemblage similarity for each taxon set and site to assess the relative contributions of spatial distance and nutrient availability distance. Then, we evaluated the potentially structuring effect of tree composition over all other taxa. The similarity of nutrient content in the litter and topsoil had a stronger and more consistent selective effect than did dispersal limitation, particularly for bacteria, fungi, and trees at the plot level. Ground insects, the only group assessed with the capacity of active dispersal, had the highest species turnover and the flattest nonsignificant distance−decay relationship, suggesting that neither dispersal limitation nor nutrient availability were fundamental drivers of their community assembly at this scale of analysis. Only the fungal communities at one of our study sites were clearly coordinated with tree composition. The spatial distance at the smallest scale was more important than nutrient selection for the bacteria, fungi, and insects. The lower initial similarity and the moderate variation in composition identified by these distance-decay models, however, suggested that the effects of stochastic sampling were important at this smaller spatial scale. Our results highlight the importance of nutrients as one of the main environmental drivers of rainforest communities irrespective of organismic or propagule size and how the overriding effect of the analytical scale influences the interpretation, leading to the perception of greater importance of dispersal limitation and ecological drift over selection associated with environmental niches at decreasing observation scales

Arthropod distribution in a tropical rainforest: tackling a four dimensional puzzle

Quantifying the spatio-temporal distribution of arthropods in tropical rainforests represents a first step towards scrutinizing the global distribution of biodiversity on Earth. To date most studies have focused on narrow taxonomic groups or lack a design that allows partitioning of the components of diversity. Here, we consider an exceptionally large dataset (113,952 individuals representing 5,858 species), obtained from the San Lorenzo forest in Panama, where the phylogenetic breadth of arthropod taxa was surveyed using 14 protocols targeting the soil, litter, understory, lower and upper canopy habitats, replicated across seasons in 2003 and 2004. This dataset is used to explore the relative influence of horizontal, vertical and seasonal drivers of arthropod distribution in this forest. We considered arthropod abundance, observed and estimated species richness, additive decomposition of species richness, multiplicative partitioning of species diversity, variation in species composition, species turnover and guild structure as components of diversity. At the scale of our study (2km of distance, 40m in height and 400 days), the effects related to the vertical and seasonal dimensions were most important. Most adult arthropods were collected from the soil/litter or the upper canopy and species richness was highest in the canopy. We compared the distribution of arthropods and trees within our study system. Effects related to the seasonal dimension were stronger for arthropods than for trees. We conclude that: (1) models of beta diversity developed for tropical trees are unlikely to be applicable to tropical arthropods; (2) it is imperative that estimates of global biodiversity derived from mass collecting of arthropods in tropical rainforests embrace the strong vertical and seasonal partitioning observed here; and (3) given the high species turnover observed between seasons, global climate change may have severe consequences for rainforest arthropods1012CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQSolVin-Solvay SA; Smithsonian Institution; Smithsonian Tropical Research Institute; United Nations Environment Programme; Smithsonian Institution; Smithsonian National Museum of Natural History; European Science Foundation (ESF); Global Canopy Programme; Czech Science foundation GACR grant; European Social Fund (ESF); Ministry of Education, Youth & Sports - Czech Republic; French National Research Agency (ANR); Research Council of Norway; Grant Agency of the Czech Republi

L'ADAPTATION A LA VIE ARBORICOLE DE LA FOURMI PACHYCONDYLA GOELDII (HYMENOPTERA (PONERIN))

PACHYCONDYLA GOELDII EST L'UNE DES RARES ESPECES DE FOURMIS PRIMITIVES DE LA SOUS-FAMILLE DES PONERIN QUI SOIT STRICTEMENT ARBORICOLE. OR, LA VIE ARBORICOLE EST UN CARACTERE APPARU SECONDAIREMENT CHEZ LES FOURMIS ET PARTAGE PRINCIPALEMENT PAR DES ESPECES DITES EVOLUEES. LES ASPECTS DE LA BIOLOGIE DE P. GOELDII ONT DONC ETE ETUDIES AFIN DE DETERMINER DANS QUELLE MESURE CETTE ESPECE POUVAIT ETRE QUALIFIEE D'EVOLUEE PARMI LES FOURMIS PRIMITIVES. LE SOL ET LE MILIEU ARBORICOLE SONT DEUX ENVIRONNEMENTS QUI DIFFERENT PAR DE NOMBREUX PARAMETRES. PARMI CEUX-CI, LA STRUCTURE MEME DU MILIEU ARBORICOLE NECESSITE L'EXISTENCE DE PELOTES ADHESIVES POUR UNE BONNE ADHESION LORS DES DEPLACEMENTS SUR LES PLANTES. MAIS CE CARACTERE EST PARTAGE PAR LA TRES GRANDE MAJORITE DES ESPECES ET NE CONSTITUE DONC PAS UN CRITERE DE DISTINCTION, BIEN QU'IL SOIT UN PRE-REQUIS INDISPENSABLE A L'APPARITION DE LA VIE ARBORICOLE. LE NOMBRE LIMITE DE SITES DE NIDIFICATION FAVORABLES EST UN DES PRINCIPAUX FACTEURS LIMITANTS DU MILIEU ARBORICOLE. P. GOELDII EST L'UNE DES RARES ESPECES CAPABLES D'INITIER DES JARDINS DE FOURMIS, CE QUI LUI PERMET DE S'AFFRANCHIR DE LA DEPENDANCE VIS-A-VIS DE STRUCTURES PREEXISTANTES. L'ENSEMBLE DES ELEMENTS COMPORTEMENTAUX ET ECOLOGIQUES CONCERNANT SON MODE DE NIDIFICATION, AINSI QUE L'EXISTENCE DE CHENILLES PARASITANT LES EPIPHYTES DU JARDIN EN PRESENCE DE CETTE FOURMI, MONTRENT CLAIREMENT QUE LE MODE DE VIE ARBORICOLE DE P. GOELDII N'EST PAS UN PHENOMENE RECENT. PAR AILLEURS, LES ASSOCIATIONS PREFERENTIELLES AVEC CERTAINS EPIPHYTES QUI PEUVENT ETRE EXPLIQUEES, AU MOINS EN PARTIE, PAR LA PREFERENCE DE CETTE FOURMI POUR LES MILIEUX TRES ENSOLEILLES TEMOIGNE D'UNE CERTAINE SPECIALISATION VOIRE D'UNE COADAPTATION. CES RESULTATS DEMONTRENT QUE L'ELEMENT ESSENTIEL A L'ORIGINE DU SUCCES DE P. GOELDII EST DE NATURE PRINCIPALEMENT COMPORTEMENTALE. LE SECOND ELEMENT IMPORTANT CONSIDERE CONCERNE LES RESSOURCES ALIMENTAIRES. LE COMPORTEMENT PREDATEUR DES PACHYCONDYLA ARBORICOLES NE DIFFERE PAS DE CELUI DES TERRICOLES ET PRESENTE MEME DES CARACTERES QUI PEUVENT ETRE VUS COMME ETANT ARCHAIQUES. NEANMOINS, LA VITESSE DE DEPLACEMENT DES OUVRIERES DE P. GOELDII, COUPLEE A LA POSSESSION D'UN VENIN FORTEMENT PARALYSANT, LUI PERMET DE CAPTURER ET D'IMMOBILISER LA MAJORITE DES PROIES RENCONTREES. LES PEPTIDES ANTI-INSECTES DU VENIN PRESENTENT DES VARIATIONS INTERSPECIFIQUES PLUS OU MOINS IMPORTANTES DONT CERTAINES PEUVENT ETRE CORRELEES AU MODE DE VIE ARBORICOLE. L'ADAPTATION COMPORTEMENTALE DE CETTE ESPECE APPARAIT DONC FAVORISEE PAR CERTAINES MODIFICATIONS PHYSIOLOGIQUES.PARIS13-BU Sciences (930792102) / SudocSudocFranceF

Data from: Resource use and food preferences in understorey ant communities along a complete elevational gradient in Papua New Guinea

Elevational gradients provide an interesting opportunity for studying the effect of climatic drivers over short distances on the various facets of biodiversity. It is globally assumed that the decrease in species richness with increasing elevation follows mainly the decrease in ecosystem productivity, but studies on functional diversity still remain limited. Here, we investigated how resource use and food preferences by both individual ant species and communities foraging in the understorey vary with elevation along a complete elevational gradient (200 to 3200 m a.s.l.). Five bait types reflecting some of the main ecosystem processes in which ants are involved were tested: mutualism (sucrose and melezitose), predation (live termites) and detritivory (crushed insects and chicken faeces). The observed monotonic decrease in both species richness and occurrences with elevation increase was accompanied by changes in some of the tested ecosystem processes. Such variations can be explained by resource availability and/or resource limitation: predation and bird faeces removal decreased with increasing elevation possibly reflecting a decline in species able to use these resources, while insect detritivory and nectarivory were most probably driven by resource limitation (or absence of limitation), as their relative use did not change along the gradient. As a consequence, resource attractiveness (i.e., food preferences at the species level) appears as an important factor in driving community structuring in ants together with the abiotic environmental conditions