Winter is coming: harsh environments limit independent reproduction of cooperative-breeding queens in a socially polymorphic ant

Cooperative breeding animals frequently inhabit harsh environments. It is widely accepted that harsh environments hinder independent reproduction, and this constraint maintains individuals in family groups. Yet the assumption that harsh ecological conditions reduce the success of members of cooperative breeding groups when breeding independently has not been experimentally tested. We addressed this shortcoming using the socially polymorphic Alpine silver ant, Formica selysi. This species has single-queen (independent breeders) and multiple-queen (cooperative breeders) colonies coexisting within populations. We placed newly mated queens emerging from each type of colony to breed alone in either a harsh or mild winter condition and recorded their brood production and survival. Queens emerging from single-queen colonies were unaffected by the winter condition and were more successful at founding a nest independently than queens from multiple-queen colonies. By contrast, queens from multiple-queen colonies had higher mortality after a harsh than after a mild winter. These results support the long-held assumption that harsh environments constrain independent reproduction of members of cooperative breeding groups

Utilisation de la microtomographie à rayons X pour suivre le séchage convectif de boues d'épuration

peer reviewedX-ray microtomography is proposed as a new tool to investigate the evolution of size, shape and texture of soft materials during a drying operation. This study is focused on the drying of mechanically dewatered sludges from a secondary wastewater treatment. The shrinkage phenomenon is shown to play a crucial role in the control of the drying process. The shrinkage curves are determined by analysing the shape and size of cross sectional microtomographic images of sludge extrudates at different levels of drying. The observation of drying and shrinkage curves allows us to determine 3 critical water content values, which define different drying zones where extragranular, intragranular or mixed limitations prevail. When drying is externally controlled. the decrease of the drying rate observed during experiments can be related to the reduction of the external area of the sample, i.e., to shrinkage. When drying is internally controlled, resistances inside the solid govern the process. Between these two extreme situations, the drying rate reduction is the result of both the external area decrease and the development of internal resistances limiting drying. A multizone model is proposed to describe quantitatively these observations. The analysis of the internal texture of the Sludge extrudates reveal, crack formation at the end of the drying process. The onset of crack formation is clearly related to the appearance of internal transfer limitations. i.e., humidity and temperature gradients inside the material

Analyse d'images obtenues par microtomographie à rayons X d'un catalyseur de type xérogel Pd-Ag/SiO2 supporté sur une mousse de Al2O3

peer reviewedIn order to preshape and mechanically strengthen, Pd-Ag/SiO2 xerogel catalysts were carried out in Al2O3 foams (pore-sizes similar to40 mum). The final material consists of a Pd-Ag/SiO2 xerogel immobilized in the open cells of the alumina foam. The localization of the xerogel catalyst in alumina foams of various pore structure was studied by X-ray microtomography. The three-dimensional (3D) porous structure was reconstructed from the consecutive cross-sections obtained by this technique. Total porosity, porous density distribution, and pore-size distribution were determined by image analysis on the free and impregnated supports. Our results show that the success of the used impregnation technique depends on the pore structure of the support. (C) 2004 Elsevier B.V. All rights reserved

Cooperation, conflicts and individual reproductive decisions in the annual societies of bumble bees (Bombus terrestris)

L’existence de conflits est une caractéristique inhérente aux sociétés animales dont la structure génétique est non clonale. L’objectif principal de cette thèse était d’étudier les décisions reproductives individuelles des ouvrières en lien avec la dynamique coopération/conflit dans les sociétés annuelles du bourdon Bombus terrestris. Les colonies de B. terrestris présentent la particularité de se développer selon deux phases distinctes : une phase sociale caractérisée par une coopération altruiste des ouvrières et une phase de compétition durant laquelle les ouvrières entrent en conflit entre elles et avec la reine pour la production des mâles. L’analyse détaillée du comportement de dérive en conditions semi-naturelles a permis de démontrer l’existence d’une stratégie de reproduction supplémentaire pour les ouvrières ; quand le conflit s’exprime, certaines ouvrières fertiles quittent leur nid pour se reproduire dans les colonies voisines de la même espèce. Cette stratégie alternative de reproduction permet aux ouvrières d’éviter l’inhibition reproductive au sein de leur nid et d’optimiser ainsi leur inclusive fitness. Nos études ont de plus révélé que les ouvrières ajustent de façon adaptée leur comportement reproducteur à l’environnement social. La grande plasticité reproductive des ouvrières repose sur leur capacité à détecter et à traiter de multiples informations pertinentes de leur environnement social. Enfin, les résultats de cette thèse suggèrent l’existence d’une stratégie de défense coloniale contre le parasitisme reproductif des ouvrières. De part leur signature chimique spécifique, les parasites potentiels sont reconnus et discriminés comportementalement à l‘entrée du nid par les gardes. Cette pluralité de stratégie de reproduction à la disposition des ouvrières est marginale au sein des hyménoptères sociaux, et les résultats obtenus de ce travail nous conduisent à discuter les traits d’histoire de vie de B. terrestris qui ont pu favoriser leur évolution.Conflicts are inherent characteristics of non-clonal animal societies. The main goal of this thesis was to study the individual reproductive decisions of workers in relation with the cooperation/conflict dynamics in the annual bumblebee Bombus terretris. Colonies of B. terretris have the particularity to go through two distinct phases : a social phase characterized by an altruistic cooperation from workers and a competition phase during which the queen and workers compete for the production of males. The study of worker's behaviour in semi-natural conditions allowed to demonstrate the existence of an additional reproductive strategy for workers ; when the conflict is expressed, some fertile workers leave their nest to reproduce in neighbouring colonies of the same species. This alternative reproductive strategy allows workers to avoid reproductive inhibition in their nest and thus to optimize their inclusive fitness. Workers also adjust their reproductive behaviour to their social environment, in line with their reproductive interests. This high reproductive plasticity of workers relies on their ability to detect and process the multiple relevant signals of their social environment. Finally, the results of this thesis suggest the existence of a colonial defence strategy against worker reproductive parasitism. By their specific chemical signature, potential parasites are recognized and behaviourlly discriminated by guards at the nest-entrance. The multiple reproductive strategies of bumble bee workers appear marginal in social Hymenoptera, and the life history traits of B. terretris which could have promoted this diversification are discussed

Cooperation by ant queens during colony-founding perpetuates alternative forms of social organization

ABSTRACT: Key social traits, like queen number in eusocial insect colonies, have long been considered plastic, but the recent finding that colony social organization is under strict genetic control in multiple ant lineages challenges this view. This begs the question of which hardwired behavioral mechanism(s) generate alternative forms of social organization during colony development. We addressed this question in the Alpine silver ant, Formica selysi, a species with two social forms determined by a supergene. Queens that carry exclusively the M haplotype are produced by and live in monogyne (= single-queen) colonies, whereas queens that carry at least one copy of the P haplotype are produced by and live in polygyne (= multiple-queen) colonies. With extensive field samplings and laboratory experiments, we show that both types of queens successfully establish colonies independently, without being accompanied by workers, but that they do so in contrasting ways. Monogyne queens were generally intolerant of other queens and founded colonies solitarily, whereas polygyne queens were mutually attracted to each other and mainly founded colonies cooperatively. These associations persisted for months after worker emergence, suggesting that cooperative colony-founding leads to permanent multiple queening. Overall, our study shows that queens of each social form found colonies independently in the field but that P-carrying queens are more likely to cooperate, thereby contributing to perpetuate alternative forms of social organization. SIGNIFICANCE STATEMENT: Understanding the genetic and behavioral underpinnings of social organization is a major goal in evolutionary biology. Recent studies have shown that colony social organization is controlled by supergenes in multiple ant lineages. But the behavioral processes linking the genotype of a queen to the type of colony she will form remain largely unknown. Here, we show that in Alpine silver ants, alternative supergene genotypes are associated with different levels of social attraction and tolerance in young queens. These hardwired differences in social traits make queens carrying the P supergene haplotype more prone to cooperate and form durable associations during independent colony-founding. These findings help explain how genetic variants induce alternative forms of social organization during the ontogeny of a colony. They also illustrate how simple phenotypic differences at the individual level can result in large differences at higher levels of organization. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s00265-021-03105-1

Suivi du procédé de séchage thermique de boues d'épuration par microtomographie aux rayons X

peer reviewe

Data from: Evolution of ageing, costs of reproduction and the fecundity–longevity trade-off in eusocial insects

Eusocial insects provide special opportunities to elucidate the evolution of ageing as queens have apparently evaded costs of reproduction and reversed the fecundity-longevity trade-off generally observed in non-social organisms. But how reproduction affects longevity in eusocial insects has rarely been tested experimentally. In this study, we took advantage of the reproductive plasticity of workers to test the causal role of reproduction in determining longevity in eusocial insects. Using the eusocial bumblebee Bombus terrestris, we found that, in whole colonies, in which workers could freely 'choose' whether to become reproductive, workers' level of ovarian activation was significantly positively associated with longevity and ovary-active workers significantly outlived ovary-inactive workers. By contrast, when reproductivity was experimentally induced in randomly-selected workers, thereby decoupling it from other traits, workers' level of ovarian activation was significantly negatively associated with longevity and ovary-active workers were significantly less long-lived than ovary-inactive workers. These findings show that workers experience costs of reproduction and suggest that intrinsically high-quality individuals can overcome these costs. They also raise the possibility that eusocial insect queens exhibit condition-dependent longevity and hence call into question whether eusociality entails a truly reversed fecundity-longevity trade-off involving a fundamental remodelling of conserved genetic and endocrine networks underpinning ageing

X-ray microtomography : a new tool to follow soft material shrinkage during convective drying

peer reviewe