Traits allowing some ant species to nest syntopically with the fire ant Solenopsis saevissima in its native range

Supercolonies of the red fire ant Solenopsis saevissima （Smith） develop in disturbed environments and likely alter the ant community in the native range of the species. For example, in French Guiana only 8 ant species were repeatedly noted as nesting in close vicinity to its mounds. Here, we verified if a shared set of biological, ecological, and behavioral traits might explain how these 8 species are able to nest in the presence of S. saevissima. We did not find this to be the case. We did find, however, that all of them are able to live in disturbed habitats. It is likely that over the course of evolution each of these species acquired the capacity to live syntopically with S. saevissima through its own set of traits, where colony size （4 species develop large colonies）, cuticular compounds which do not trigger aggressiveness （6 species） and submissive behaviors （4 species） complement each other.

Larval interference competition between the native Neotropical mosquito Limatus durhamii and the invasive Aedes aegypti improves the fitness of both species

Interspecific competition with native species during biological invasions can sometimes limit alien expansion.We aimed to determine the potential ecological effects of Limatus durhamii Theobald 1901,a native Neotropical mosquito (Diptera:Culicidae) species,on the invasive species Aedes (Stegomyia)aegypti (Linnaeus 1762)that breeds in the same artificial water containers.Development time and adult dry mass were measured in 3 rearing conditions:control (a single larva),intraspecific competition (2 conspecific larvae),and interspecific competition (2 heterospecific larvae).Food was provided ad libitum to eliminate exploitative competition.For Ae.aegypti,development time was not affected by interspecific interference competition (nonsignificant differences with the control)and the adult dry mass was significantly higher,meaning that individual fitness likely increased.Yet,because previous studies showed longer development time and lighter adults during competition with other invasive mosquitoes,it is likely that Ae.aegypti can express a different phenotype depending on the competing species.The similar pattern found for Li.durhamii females and the nonsignificant difference with the control for males explain in part why this species can compete with Ae.aegypti.

An uneasy alliance:a nesting association between aggressive ants and equally fierce social wasps

Although the Neotropical territorially dominant arboreal ant Azteca chartifex Forel is very aggressive towards any intruder,its populous colonies tolerate the close presence of the fierce polistine wasp Polybia rejecta(F.).In French Guiana,83.33%of the 48 P.rejecta nests recorded were found side by side with those of A.chartifex.This nesting association results in mutual protection from predators(i.e.,the wasps protected from army ants;the ants protected from birds).We conducted field studies,laboratorybased behavioral experiments and chemical analyses to elucidate the mechanisms allowing the persistence of this association.Due to differences in the cuticular profiles of the two species,we eliminated the possibility of chemical mimicry.Also,analyses of the carton nests did not reveal traces of marking on the envelopes.Because ant forager flows were not perturbed by extracts from the wasps’Dufour’s and venom glands,we rejected any hypothetical action of repulsive chemicals.Nevertheless,we noted that the wasps"scraped"the surface of the upper part of their nest envelope using their mandibles,likely removing the ants'scent trails,and an experiment showed that ant foragers were perturbed by the removal of their scent trails.This leads us to use the term"erasure hypothesis."Thus,this nesting association persists thanks to a relative tolerance by the ants towards wasp presence and the behavior of the wasps that allows them to"contain"their associated ants through the elimination of their scent trails,direct attacks,"wing-buzzing"behavior and ejecting the ants.

The Guianese population of the fire ant Solenopsis saevissima is unicolonial

In this study, conducted in French Guiana, a part of the native range of the fire ant Solenopsis saevissima, we compared the cuticular hydrocarbon profiles of media workers with previous results based on intraspecific aggressiveness tests. We noted a strong congruence between the two studies permitting us to delimit 2 supercolonies extending over large distances （up to 54 kin）, a phenomenon known as unicoloniality. Solenopsis geminata workers, taken as an out-group for cluster analyses, have a very different cuticular hydrocarbon profile. Because S. saevissima has been reported outside its native range, our conclusion is that this species has the potential to become invasive because unicoloniality （i.e., the main attribute for ants to become invasive） was shown at least for the Guianese population.

The dynamics of ant mosaics in tropical rainforests characterized using the Self-Organizing Map algorithm

Ants, the most abundant taxa among canopy-dwelling animals in tropical rainforests, are mostly represented by territorially dominant arboreal ants （TDAs） whose territories are distributed in a mosaic pattern （arboreal ant mosaics）. Large TDA colonies regulate insect herbivores, with implications for forestry and agronomy. What generates these mosaics in vegetal formations, which are dynamic, still needs to be better understood. So, from empirical research based on 3 Cameroonian tree species （Lophira alata, Ochnaceae; Anthocleista vogelii, Gentianaceae; and Barteriafistulosa, Passifloraceae）, we used the Self-Organizing Map （SOM, neural network） to illustrate the succession of TDAs as their host trees grow and age. The SOM separated the trees by species and by size for L. alata, which can reach 60 m in height and live several centuries. An ontogenic succession of TDAs from sapling to mature trees is shown, and some ecological traits are highlighted for certain TDAs. Also, because the SOM permits the analysis of data with many zeroes with no effect of outliers on the overall scatterplot distributions, we obtained ecological information on rare species. Finally, the SOM permitted us to show that functional groups cannot be selected at the genus level as congeneric species can have very different ecological niches, something particularly true for Crematogaster spp., which include a species specifically associated with B. fistulosa, nondominant species and TDAs. Therefore, the SOM permitted the complex relationships between TDAs and their growing host trees to be analyzed, while also providing new information on the ecological traits of the ant species involved.