Abstract: Termites represent one of the most abundant belowground animal taxa in tropical rainforests, where their species richness is much higher than in any other ecosystem. This high diversity in soil ecosystems is however difficult to explain by classical Hutchinsonian niche theory, as there is little evidence for spatial or temporal separation between species. Using delta C-13 and delta N-15 isotopic ratios, we tested if resource partitioning along the humification gradient occurs; in neotropical soldierless termites of the Anoplotermes-group. Two distinct sites were investigated to check if interspecific differences are transposable between sites. Significant differences in delta N-15 were found between species of the Anoplotermes-group. Although some species displayed higher intersite delta N-15 variation than others, species-average delta N-15 values for both sites were highly correlated, showing that sympatric soldierless soil-feeding termites feed on distinct components of the soil. Our data also suggest that some species are more likely to shift along this gradient than others, in response to overall habitat conditions or to the presence of competitors. Feeding niche differentiation can therefore account for the high species richness and diversity of soldierless soil-feeding termites in neotropical rainforests. (C) 2009 Elsevier Ltd. All rights reserved.

Abstract: The diversion of a host's energy by a symbiont for its own benefit is a major source of instability in horizontally-transmitted mutualisms. This instability can be counter-balanced by the host's retaliation against exploiters. Such responses are crucial to the maintenance of the relationship. We focus on this issue in an obligate ant-plant mutualism in which the ants are known to partially castrate their host plant. We studied plant responses to various levels of castration in terms of (1) global vegetative investment and (2) investment in myrmecophytic traits. Castration led to a higher plant growth rate, signalling a novel case of gigantism induced by parasitic castration. On the other hand, completely castrated plants produced smaller nesting and food resources (i.e. leaf pouches and extra floral nectaries). Since the number of worker larvae is correlated to the volume of the leaf pouches, such a decrease in the investment in myrmecophytic traits demonstrates for the first time the existence of inducible retaliation mechanisms against too virulent castrating ants. Over time, this mechanism promotes an intermediate level of castration and enhances the stability of the mutualistic relationship by providing the ants with more living space while allowing the plant to reproduce. © 2013 Springer Science+Business Media New York.

Abstract: A variety of arthropods, particularly insects, have developed myrmecophilous interactions with ants to gain access to resources and/or for protection. Among these myrmecophiles, only a few examples have been documented in the Coccinellidae, most of them involving species able to feed on ant-tended Hemiptera. We report here a new case of obligate myrmecophily in the coccinellid Diomus thoracicus. Larvae are invariably and exclusively found in the nests of the ant Wasmannia auropunctata and seem to rely on ant brood as their only food source. Not only do ant workers show no aggressiveness toward the D. thoracicus larvae in their behavioral interactions at the colonial level, but also at the species level; while coccinellid adults are always attacked. The integration of the larvae inside of the ant nests is based on their chemical mimicry of the host's cuticular cues. Therefore, given the presence of the D. thoracicus larvae inside of the ant's nest, their predation on Wasmannia brood and their chemical mimicry, this species can be considered a specific parasite of W. auropunctata. Overall, this new case of myrmecophily not only specifically involves a highly invasive ant species, but also provides insights into the evolution of myrmecophily and myrmecophagy in coccinellids.

Abstract: We examined fine-scale heterogeneity of environmental conditions in a primary rain forest in French Guiana to describe variation in microhabitats that plants may experience during establishment. We characterized both the range as well as the spatial structuring of 11 environmental factors important for seedling establishment in six hexagonal sampling grids, one each in gap and understory sites at three points representing the predominant geomorphic units in this primary forest. Each grid contained 37 sampling points separated by 31 cm-20 m. Monte-Carlo tests of semivariograms against complete spatial randomness indicated that for many variables in all six sampling grids, spatial dependence did not exceed 1 m. A principal component analysis of all sampling points revealed a lack of spatial microhabitat structure, rather than homogeneous patches associated with canopy structure or geomorphology. Our results suggest that ample fine-scale spatial heterogeneity exists to support the coexistence of plant species with differential abiotic requirements for regeneration.

Abstract: The floral development of Syngonium angustatum is analysed in the context of a recently published molecular phylogeny of the Araceae. The initiation of discoid floral primordia occurs acropetally on the surface of the inflorescence. Female flowers, atypical bisexual flowers, sterile male flowers and male flowers are inserted on the same phyllotactic spirals on the spadix. Stamen primordia are initiated simultaneously on the periphery of more or less circular floral primordia. There are four stamens per flower (rarely three). In a synandrium, the fusion of stamens occurs very early during their developmental cycle. In some flowers one or two stamens remain free. The staminodes are also initiated on the periphery of the discoid floral primordium and their number varies from four to six. The growth of the fused staminodes will eventually form a longitudinal cavity in the centre of the mature synandrode. On the synandrodes located near the female zone, one or two staminodes remain free during development. No atypical bisexual flowers were observed on the inflorescence of Syngonium. The presence of a few calcium oxalate crystals was observed on the surface of all types of flowers. All the atypical flowers located at the base of the sterile zone corresponded to sterile male flowers and resulted from a more or less random disorganisation of the typical structure of a synandrode. In the Aroideae, free stamens or staminodes represent a plesiomorphic condition. The association of synandria and synandrodes is present in all early diverging genera of the tribe Caladieae and could represent the ancestral state. It is not clear if free stamens have evolved once or twice in the tribe Caladieae, both scenarios are possible.