Structure, fonction et évolution des glandes exocrines termites

Termites represent a group of eusocial insects that live in colonies containing up to hundreds to millions. They are highly abundant, exceeding in tropics 6,000 individuals per square meter. Due to their abundance, termites represent an important food source for a wide variety of predators. At the same time, termite defensive adaptations allow the colonies to overcome the predator pressures, being extremely evolutionary successful. This achievement is explained by the development of a complex communication system operated by a rich set of exocrine glands. As many as 20 different exocrine organs are known in termites. Some of these organs had received negligible attention being only known by anecdotal observation. One of these was the labral gland. In this study, I examined the structure and ultrastructure of the labrum in soldiers of 28 species, workers of 28 species and imagoes of 33 species across termites’ main representatives, and in the wood roach Cryptocercus. The labral gland was present in all species and castes, and comprises two secretory regions located on the ventral side of the labrum and the dorso–apical part of the hypopharynx, respectively. The epithelium of the gland consisted of class 1 secretory cells, with an addition of class 3 secretory cells in soldiers of few species. A common feature of the secretory cells was the abundance of smooth endoplasmic reticulum (an organelle known to produce lipidic and often volatile secretions), long microvilli with a channel inside, which releases the secretion through a modified cuticle. According to the structure, ultrastructure and behavioural experiments, my results suggest that the labral gland is involved in defensive communication after encounter to an alien. On the other hand, other glands are extensively studied in some castes but have received almost no attention in other castes. It is the case of the frontal gland, an organ without any equivalent among other animals. The frontal gland is well known in soldiers and imagoes but not much was known about it in workers. In order to provide a complete picture of the evolution of this gland in termite workers and consequently in termites, I studied it in 41 additional species across Neoisoptera. The frontal gland of these species was formed by class 1 secretory cells only, and occured as an epithelial without reservoir in all cases. My data suggest that the frontal gland would have caste–specific evolutionary routes, being its ancestral form epithelial with reservoir in soldiers and imagoes, while epithelial thickening in workers. This study was the first to provide a comprehensive picture of the structure of the labral and frontal gland across all termite taxa and castes, providing fundamental information to enhance our understanding about the evolution and social behaviour of Isoptera.Les termites représentent un groupe d'insectes eusociaux qui vivent dans des colonies contenant des centaines, voire des millions d’individus. Ils sont très abondants, dépassant 6 000 individus par mètre carré sous les tropiques. En raison de leur abondance, les termites représentent une source de nourriture importante pour une grande variété de prédateurs. Les adaptations défensives des termites permettent aux colonies de surmonter avec succès les pressions des prédateurs. Cette réussite s’explique par le développement d’un système de communication complexe opéré par un riche ensemble de glandes exocrines. Pas moins de 20 glandes exocrines différentes sont connues chez les termites. Certaines de ces glandes avaient fait l’objet d’une attention négligeable, n’étant connues que par des observations anecdotiques.L'une d'elles était la glande labrale. Dans cette étude, j’ai examiné la structure et l’ultrastructure du labrum chez des soldats de 28 espèces, des ouvriers de 28 espèces et des imagos de 33 espèces parmi les principaux représentants des termites, ainsi que chez la blatte xylophage Cryptocercus.La glande labrale était présente chez toutes les espèces et castes et comprenait deux régions de sécrétion situées respectivement sur la face ventrale du labrum et la partie dorso-apicale de l'hypopharynx. L'épithélium de la glande était constitué de cellules sécrétrices de classe 1,auxquelles s'ajoutaient des cellules sécrétrices de classe 3 chez les soldats de quelques espèces.Une caractéristique commune des cellules sécrétrices était l'abondance de réticulum endoplasmique lisse (un organite connu pour produire des sécrétions lipidiques et souvent volatiles), de longues microvillosités avec un canal à l'intérieur, qui libèrent la sécrétion à travers une cuticule modifiée. D’après ces expériences sur la structure, l'ultrastructure et le comportement,mes résultats suggèrent que la glande labrale est impliquée dans la communication défensive après une rencontre avec un étranger. D'autre part, d'autres glandes sont étudiées de manière approfondie chez certaines castes mais n'ont pratiquement pas fait l'objet d'attention chez d'autres castes. C'est le cas de la glande frontale, organe sans équivalent parmi les autres animaux. La glande frontale est bien connue des soldats et des imagos, mais elle était peu connue chez les ouvriers. Afin de brosser un tableau complet de l'évolution de cette glande chez les termites et, par conséquent, chez les termites, je l'ai étudiée chez 41 espèces supplémentaires sur l'ensemble des néoisoptères. La glande frontale de ces espèces était formée uniquement de cellules sécrétrices de classe 1 et se présentait comme un épithélium sans réservoir dans tous les cas. Mes données Abstract 151 suggèrent que la glande frontale aurait des voies d'évolution propres à la caste, avec une forme ancestrale épithéliale avec réservoir chez les soldats et les imagos, mais en n’étant qu’un épaississement épithélial chez les ouvriers. Cette étude a été la première à fournir une image complète de la structure des glandes labrale et frontale à travers tous les taxons et castes des termites, fournissant des informations fondamentales pour améliorer notre compréhension de l'évolution et du comportement social des Isoptera

Changes in Diversity and Community Composition of Root Endophytic Fungi Associated with Aristolochia chilensis along an Aridity Gradient in the Atacama Desert

Despite the widespread occurrence of fungal endophytes (FE) in plants inhabiting arid ecosystems, the environmental and soil factors that modulate changes in FE diversity and community composition along an aridity gradient have been little explored. We studied three locations along the coast of the Atacama Desert in Chile, in which the plant Aristolochia chilensis naturally grows, and that differ in their aridity gradient from hyper-arid to semi-arid. We evaluated if root-associated FE diversity (frequency, richness and diversity indexes) and community composition vary as a function of aridity. Additionally, we assessed whether edaphic factors co-varying with aridity (soil water potential, soil moisture, pH and nutrients) may structure FE communities. We expected that FE diversity would gradually increase towards the aridity gradient declines, and that those locations that had the most contrasting environments would show more dissimilar FE communities. We found that richness indexes were inversely related to aridity, although this pattern was only partially observed for FE frequency and diversity. FE community composition was dissimilar among contrasting locations, and soil water availability significantly influenced FE community composition across the gradient. The results indicate that FE diversity and community composition associated with A. chilensis relate to differences in the aridity level across the gradient. Overall, our findings reveal the importance of climate-related factors in shaping changes in diversity, structure and distribution of FE in desert ecosystems

X-ray computed tomography reveals that intraspecific competition promotes soldier differentiation in a one-piece nesting termite

© 2017 The Netherlands Entomological Society Investment in soldier production in eusocial lineages involves a trade-off between maintenance costs and defense benefits. Termites are eusocial insects that live in colonies organized into three castes: primary reproductives, soldiers, and workers or pseudergates. Neotermes chilensis (Blanchard) (Isoptera: Kalotermitidae) is a one-piece nesting termite that nests and forages in a single piece of wood. Two scenarios may be of importance in a defense context of one-piece nesting termites: during swarms, when colonies may be invaded by winged termites (alates) in search of a place to found a new colony, and when colonies of conspecifics are present within the same substrate. It was hypothesized that the ratio of soldiers to non-soldiers would be higher at the onset of the swarming period and in substrates bearing more than one termite colony. A method based on X-ray computed tomography (CT) was developed to study gallery connectivity in colon

Tonsuritermes, a new soldierless termite genus and two new species from South America (Blattaria: Isoptera: Termitidae: Apicotermitinae)

Constantini, Joice P., Carrijo, Tiago Fernandes, Palma-Onetto, Valeria, Scheffrahn, Rudolf, Carnohan, Lucas Paul, Šobotník, Jan, Cancello, Eliana M. (2018): Tonsuritermes, a new soldierless termite genus and two new species from South America (Blattaria: Isoptera: Termitidae: Apicotermitinae). Zootaxa 4531 (3): 383-394, DOI: https://doi.org/10.11646/zootaxa.4531.3.

Does anyone need mouth rinse? An expert view

Focusing on the clinical implications in terms of plaque reduction and the associated potential outcomes such as reduced caries and gingivitis, Professor Anthony Roberts expands on the significance, importance and relevance of the data to consider its potential for change within everyday dental practice