Seasonality influences ant-mediated nutrient acquisition (myrmecotrophy) by a Neotropical myrmecophyte

International audienceTachia guianensis (Gentianaceae), a Neotropical understory myrmecophyte, shelters ant colonies in its hollow trunks and branches (domatia). In turn, it is protected from defoliators and obtains nutrients from ant-produced wastes (myrmecotrophy). Aiming to verify if seasonality influences nitrogen assimilation via ant wastes using the stable isotope nitrogen-15, we first studied Tachia's phenology and its seasonal leaf production, and then the life cycle of its two more frequent guest ant species. We found that leaf production was much higher during the rainy than the dry season. Mature guest ant colonies produced sexuals regardless of the season and the net weight of the waste piles inside the domatia did not vary between seasons, so that the availability of nutrients to their host plant is steady year-long. By providing the two most frequent mutualistic guest ant species with food enriched with nitrogen-15, we showed that Tachia individuals assimilate more nitrogen from ant wastes during the rainy season, when the plant is physiologically active, compared to the dry season. Thus, one can deduce that the increase in nitrogen assimilation during the rainy season is determined by the increase in Tachia's physiological activity during that season. Information gathered through a bibliographic compilation confirms that none of the 15 ant species known to be associated with myrmecophytes for which the life cycle was studied is characterized by seasonal reproduction (which would result in fluctuating waste production). The same is true for 49.7% of 167 tropical ant species (seasonal production for the remaining species). We concluded that, in contrast to the non-seasonal ant colony reproductive cycle, Tachia's phenology determines the myrmecotrophic assimilation rate

Nutrient provisioning of its host myrmecophytic tree by a temporary social parasite of a plant-ant

One of the most advanced ant–plant mutualisms is represented by myrmecophytes sheltering colonies of some plant-ant species in hollow structures called domatia. In turn, the myrmecophytes benefit from biotic protection and sometimes nutrient provisioning (myrmecotrophy). Furthermore, over the course of evolution, some ant species have become social parasites of others. In this general context, we studied the relationship between its host trees and Azteca andreae (Dolichoderinae), a temporary social parasite of the plant-ant Azteca ovaticeps, and, as such, obligatorily associated with myrmecophytic Cecropia obtusa trees (Urticaceae). A first experiment showed that the δ15N values of the young leaves of Cecropia sheltering a mature A. andreae colony were very similar to those for trees sheltering Azteca alfari or A. ovaticeps, two typical Cecropia mutualists for which myrmecotrophy is known. In a second experiment, by injecting a 15N-labelled glycine solution into locusts given as prey to A. andreae colonies, we triggered an increase in δ15N in the young leaves of their host Cecropia. Thus, 15N passed from the prey to the host trees, explaining the outcomes of the first experiment. We discuss these results in light of the notion of "by-product benefits"

Climate change impact on Amazonian ant gardens

International audienceIn Amazonia higher Atlantic sea surface temperatures, greenhouse gasses, deforestation and El Niño events result in the greater frequency of severe droughts, although total rainfall has increased due to wetter rainy seasons, something confirmed in French Guiana from available climatic data (1980À2017). Aiming to study the impact of rainfall on ant gardens (i.e., arboreal ant-epiphyte mutualisms that depend on the atmosphere for water; AGs) initiated by the ponerine ant Neoponera goeldii, we conducted surveys around the Petit Saut and R egina areas (mean annual rainfall: %3,000 mm and %4,000 mm, respectively). Each year, near the end of the dry season we recorded the number of these AGs in 10 £ 5 m sections parallel to the roadsides. The Petit Saut survey (1993À2017) revealed that AG density along roadsides varied only slightly in "wet zones" situated along ditches, whereas in "dry zones" where the soil seasonally dries out it dropped sharply during the drastic 1997 dry season. Then, this density, low due to recurrent droughts, dropped again during the drastic successive 2015À2016 dry seasons. In the R egina survey (2006À2017), we had the opportunity to follow the establishment of AGs in a "dry zone". It was represented by a typical sigmoidal curve and then it stabilized with AG densities higher than at its peak in 1996 in dry zones of Petit Saut, showing the importance of rainfall. Here, too, the drastic 2016 dry season adversely affected the AGs. Finally, the epiphytic composition of the AGs was mainly represented by Aechmea mertensii (a tank bromeliad), Anthurium gracile (Araceae) and Codonanthe crassifolia (Gesneriaceae), but AGs with the tank bromeliad are more resistant to droughts. These AGs are at risk in dry zones if drastic successive dry seasons occur in the future as global warming intensifies while those developing in riparian areas might survive

Les fourmis, témoins de la restauration des sites miniers

At a time when gold mining projects are proliferating in French Guiana, the restoration of former gold mining sites is an environmental issue in French Guiana. Ants are proving to be good biological indicators of the return of the forest.Alors que les projets miniers aurifères se multiplient en Guyane, la restauration des anciens sites miniers aurifères est un enjeu environnemental en Guyane. Les fourmis se révèlent de bons indicateurs biologiques du retour de la forêt

Hollow Internodes Permit a Neotropical Understory Plant to Shelter Multiple Mutualistic Ant Species, Obtaining Protection and Nutrient Provisioning (Myrmecotrophy)

International audienceThe Neotropical understory plant Tachia guianensis (Gentianaceae)—known to shelter the colonies of several ant species in its hollow trunks and branches—does not provide them with food rewards (e.g., extrafloral nectar). We tested whether these ants are opportunistic nesters or whether mutualistic relationships exist as for myrmecophytes or plants sheltering ant colonies in specialized hollow structures in exchange for protection from enemies and/or nutrient provisioning (myrmecotrophy). We noted 37 ant species sheltering inside T. guianensis internodes, three of them accounting for 43.5% of the cases. They protect their host plants from leaf-cutting ant defoliation and termite damage because individuals devoid of associated ants suffered significantly more attacks. Using the stable isotope 15N, we experimentally showed that the tested ant species furnish their host plants with nutrients. Therefore, a mutualism exists. However, because it is associated with numerous ant species, T. guianensis can be considered a nonspecialized myrmecophyte

Aquatic life in Neotropical rainforest canopies: Techniques using artificial phytotelmata to study the invertebrate communities inhabiting therein

International audienceIn Neotropical rainforest canopies, phytotelmata ("plant-held waters'') shelter diverse aquatic macroinvertebrate communities, including vectors of animal diseases. Studying these communities is difficult because phytotelmata are widely dispersed, hard to find from the ground and often inaccessible. We propose here a method for placing in tree crowns "artificial phytotelmata'' whose size and shape can be tailored to different research targets. The efficacy of this method was shown while comparing the patterns of community diversity of three forest formations. We noted a difference between a riparian forest and a rainforest, whereas trees alongside a dirt road cutting through that rainforest corresponded to a subset of the latter. Because rarefied species richness was significantly lower when the phytotelmata were left for three weeks rather than for six or nine weeks, we recommend leaving the phytotelmata for twelve weeks to permit predators and phoretic species to fully establish themselves. (C) 2017 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved

Host‐tree selection by the ant garden‐initiating arboreal ponerine Neoponera goeldii

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Climate change negatively affects Amazonian social wasps

Abstract The impact of climate change is intensifying in Amazonia through, among other causes, the higher frequency of both severe droughts and floods due to El Niño and La Niña events as well as an Atlantic influence. Over a 25-year period (1997–2021) we examined in French Guiana the impact of different climatic parameters on the most frequent social wasp, Polybia bistriata (Polistinae). As it commonly nests on Clusia grandiflora (Clusiaceae), its nests are easily found. Heavy rainfall, particularly during the 1999–2000 La Niña episode, negatively affected this social wasp species as the percentage of Clusia sheltering an active P. bistriata nest decreased from ≈ 40% during the pre-2000 period to zero in 2021. We conclude that extreme wet seasons related to climate change translated into the decline of this species and likely were detrimental to many other polistine wasps of north-eastern Amazonia

Highly modular pattern in ant-plant interactions involving specialized and non-specialized myrmecophytes

International audienceBecause Tachia guianensis (Gentianaceae) is a “non-specialized myrmecophyte” associated with 37 ant species, we aimed to determine if its presence alters the ant guild associated with sympatric “specialized myrmecophytes” (i.e., plants sheltering a few ant species in hollow structures). The study was conducted in a hilly zone of a neotropical rainforest where two specialized myrmecophytes grow at the bottom of the slopes, another at mid-slope, and a fourth on the hilltops. Tachia guianensis, which occurred everywhere, had its own guild of associated ant species. A network analysis showed that its connections with the four other myrmecophytes were rare and weak, the whole resulting in a highly modular pattern of interactions with one module (i.e., subnetwork) per myrmecophyte. Three ant species parasitized three out of the four specialized myrmecophytes (low nestedness noted), but were not or barely associated with T. guianensis that therefore did not influence the parasitism of specialized myrmecophytes