collaborateurs

Marjorie Labédan

Laborantin(e) chez MuséumLab

  • T: -
  • office 4006 (Sciences III)

  • Gene expression during larval caste determination and differentiation in intermediately eusocial bumblebees, and a comparative analysis with advanced eusocial honeybees Mol Ecol. 2021 Feb;30(3):718-735. doi: 10.1111/mec.

    résumé

    The queen-worker caste system of eusocial insects represents a prime example of developmental polyphenism (environmentally-induced phenotypic polymorphism) and is intrinsic to the evolution of advanced eusociality. However, the comparative molecular basis of larval caste determination and subsequent differentiation in the eusocial Hymenoptera remains poorly known. To address this issue within bees, we profiled caste-associated gene expression in female larvae of the intermediately eusocial bumblebee Bombus terrestris. In B. terrestris, female larvae experience a queen-dependent period during which their caste fate as adults is determined followed by a nutrition-sensitive period also potentially affecting caste fate but for which the evidence is weaker. We used mRNA-seq and qRT-PCR validation to isolate genes differentially expressed between each caste pathway in larvae at developmental stages before and after each of these periods. We show that differences in gene expression between caste pathways are small in totipotent larvae, then peak after the queen-dependent period. Relatively few novel (i.e., taxonomically-restricted) genes were differentially expressed between castes, though novel genes were significantly enriched in late-instar larvae in the worker pathway. We compared sets of caste-associated genes in B. terrestris with those reported from the advanced eusocial honeybee, Apis mellifera, and found significant but relatively low levels of overlap of gene lists between the two species. These results suggest both the existence of low numbers of shared toolkit genes and substantial divergence in caste-associated genes between Bombus and the advanced eusocial Apis since their last common eusocial ancestor.

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  • Endocrine control of cuticular hydrocarbon profiles during worker-to-soldier differentiation in the termite Reticulitermes flavipes J Insect Physiol. 2014 Feb;61:25-33. doi: 10.1016/j.jinsphys.2013.12.006

    résumé

    The social organization of termites, unlike that of other social insects, is characterized by a highly plastic caste system. With the exception of the alates, all other individuals in a colony remain at an immature stage of development. Workers in particular remain developmentally flexible; they can switch castes to become soldiers or neotenics. Juvenile hormone (JH) is known to play a key role in turning workers into soldiers. In this study, we analyzed differences in cuticular hydrocarbon (CHC) profiles among castes, paying particular attention to the transition of workers to soldiers, in the subterranean termite species Reticulitermes flavipes. CHCs have a fundamental function in social insects as they serve as cues in inter- and intraspecific recognition. We showed that (1) the CHC profiles of the different castes (workers, soldiers, nymphs and neotenics) are different and (2) when workers were experimentally exposed to a JH analog and thus induced to become soldiers, their CHC profiles were modified before and after the worker-presoldier molt and before and after the presoldier-soldier molt.

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  • Colony breeding structure of the invasive termite Reticulitermes urbis (Isoptera: Rhinotermitidae) J Econ Entomol. 2013 Oct;106(5):2216-24. doi: 10.1603/ec13157.

    résumé

    Invasive species cause severe environmental and economic problems. The invasive success of social insects often appears to be related to their ability to adjust their social organization to new environments. To gain a better understanding of the biology of invasive termites, this study investigated the social organization of the subterranean termite, Reticulitermes urbis, analyzing the breeding structure and the number of reproductives within colonies from three introduced populations. By using eight microsatellite loci to determine the genetic structure, it was found that all the colonies from the three populations were headed by both primary reproductives (kings and queens) and secondary reproductives (neotenics) to form extended-family colonies. R. urbis appears to be the only Reticulitermes species with a social organization based solely on extended-families in both native and introduced populations, suggesting that there is no change in their social organization on introduction. F-statistics indicated that there were few neotenics within the colonies from urban areas, which did not agree with results from previous studies and field observations. This suggests that although several neotenics may be produced, only few become active reproductives. The results also imply that the invasive success of R. urbis may be based on different reproductive strategies in urban and semiurbanized areas. The factors influencing an individual to differentiate into a neotenic in Reticulitermes species are discussed.

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  • Individual rules for trail pattern formation in Argentine ants (Linepithema humile) PLoS Comput Biol. 2012;8(7):e1002592. doi: 10.1371/journal.pcbi.1002592.

    résumé

    We studied the formation of trail patterns by Argentine ants exploring an empty arena. Using a novel imaging and analysis technique we estimated pheromone concentrations at all spatial positions in the experimental arena and at different times. Then we derived the response function of individual ants to pheromone concentrations by looking at correlations between concentrations and changes in speed or direction of the ants. Ants were found to turn in response to local pheromone concentrations, while their speed was largely unaffected by these concentrations. Ants did not integrate pheromone concentrations over time, with the concentration of pheromone in a 1 cm radius in front of the ant determining the turning angle. The response to pheromone was found to follow a Weber's Law, such that the difference between quantities of pheromone on the two sides of the ant divided by their sum determines the magnitude of the turning angle. This proportional response is in apparent contradiction with the well-established non-linear choice function used in the literature to model the results of binary bridge experiments in ant colonies (Deneubourg et al. 1990). However, agent based simulations implementing the Weber's Law response function led to the formation of trails and reproduced results reported in the literature. We show analytically that a sigmoidal response, analogous to that in the classical Deneubourg model for collective decision making, can be derived from the individual Weber-type response to pheromone concentrations that we have established in our experiments when directional noise around the preferred direction of movement of the ants is assumed.

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Tout ce qui permet de mieux comprendre, de manière évolutive, le fonctionnement de la nature : pourquoi observons-nous cela? Qu’est ce qui a conduit à ceci ? Comment est-ce arrivé ?

Utiliser les techniques modernes en biologie moléculaire pour répondre à toutes les questions que nous pourrions avoir est aussi une de mes motivations. Mon rôle est d’apporter un soutien et une aide technique afin de choisir et utiliser les techniques moléculaires les plus adaptées pour répondre aux questions posées dans les divers projets de recherche auxquels je participe.