L'investissement des adultes pour augmenter la survie des jeunes est souvent optimisé par une communication émise par les jeunes et informant les parents de leur niveau de besoin. Nous avons exploré dans cette thèse si les comportements des larves de fourmi pouvaient être des quémandes alimentaires telles que définies par les modèles de communication honnête. En effet, les fourmis, eusociales, possèdent un système de relations sociales et de coopérations qui diffère du modèle parental classiquement décrit. Nous avons donc testé chez la fourmi Ectatomma tuberculatum si les comportements des larves pouvaient refléter leur niveau de besoin et si les ouvrières apportaient la nourriture en fonction du signal comme prédit par les modèles. Nous montrons dans cette thèse que les mouvements émis par les larves ainsi qu'un composé chimique volatil larvaire pourraient tous deux intervenir et influencer l'apport alimentaire par les ouvrières. Les mouvements larvaires augmentent avec le stade de développement des larves et le composé chimique augmenterait avec le niveau d'affamement des larves. Les ouvrières, nourrices et fourrageuses, pourraient donc optimiser la répartition des ressources alimentaires de la colonie grâce à ces signaux ou indices des larves. Cependant, nous montrons aussi que plusieurs autres facteurs proximaux interviennent. Les mouvements larvaires font suite à des contacts fortuits avec les ouvrières, et l'organisation spatiale des ouvrières et des larves influencent les mouvements larvaires et le nourrissage. Des hypothèses alternatives ou complémentaires à la communication sont donc proposées. / Parental investment to increase survivability of the young is often optimised by signalling emitted by the young and informing the parents of their level of need. In this thesis, we explored whether the behaviour of ant larvae could be analysed as food solicitations as defined by honest communication models. Indeed, ants are highly social and their social relations differ from the social relation in parent-offspring systems which is usually analysed for food solicitations. We therefore tested, in the ant Ectatomma tuberculatum, whether behaviour of the larvae was correlated with the level of need and if workers provisioned larvae with food according to the intensity of the signal, as predicted by honest signalling models. We showed in this thesis that movements displayed by the larvae as well as a larval volatile emission could influence food provisioning by workers. Larval movements increase with larval developmental stage and volatile emission vary with nutritional state of the larvae. Nurse and forager workers could then optimise food resources allocation inside the nest thanks to signals or cues from the larvae. However, we also show that several other proximal factors are involved. Larval movements are not freely displayed but follow a contact with a worker, and spatial organisation of workers and larvae influences larval movements and food provisioning. Thus we propose alternative or complementary hypotheses to the communication hypothesis.

Submitted by Reginaldo Soares de Freitas (reginaldo.freitas@ufv.br) on 2016-06-09T15:32:09Z No. of bitstreams: 1 texto completo.pdf: 804627 bytes, checksum: c2b8d6549b8b514609e1554d802931a4 (MD5) / Made available in DSpace on 2016-06-09T15:32:09Z (GMT). No. of bitstreams: 1 texto completo.pdf: 804627 bytes, checksum: c2b8d6549b8b514609e1554d802931a4 (MD5) Previous issue date: 2011-03-01 / Conselho Nacional de Desenvolvimento Científico e Tecnológico / As operárias da formiga Ectatomma tuberculatum (Ectatomminae) apresentam ovários desenvolvidos e produzem ovos que são utilizados na alimentação da cria e da rainha (ovos tróficos). As vitelogeninas são as principais proteínas encontradas nos ovos de insetos, sendo potencial fonte de nutrientes para o embrião e adultos. Em insetos sociais, os níveis de vitelogenina variam entre os indivíduos e influenciam a determinação das castas reprodutivas e operárias, atividades de cuidado com a cria e forrageio, longevidade, manutenção somática e imunidade. Em formigas que produzem ovos tróficos, a vitelogenina é uma das fontes de alimento para larvas e rainhas. Em geral, a síntese de vitelogenina é regulada em nível transcricional principalmente por hormônio juvenil (HJ), mas em operárias de formigas essa relação não está muito bem caracterizada. Os objetivos deste trabalho foram verificar o período de produção de vitelogenina em operárias de E. tuberculatum e o efeito do HJ na síntese dessa proteína. A vitelogenina foi identificada a partir de extratos de ovos de rainhas e operárias por SDS-PAGE. Anticorpos anti-vitelogenina foram obtidos e utilizados para detecção dessa proteína no corpo gorduroso e na hemolinfa de operárias de diferentes idades. Também foi observado o efeito da aplicação de HJ III na síntese de vitelogenina no corpo gorduroso e nos níveis de vitelogenina circulantes na hemolinfa de operárias, através de PCR quantitativo em tempo real e ELISA. As vitelogeninas de E. tuberculatum são constituídas por dois polipeptídios de 31 e 156 kDa. Nos ovos de rainhas, a vitelogenina de 156 kDa é clivada em duas subunidades de 36 e 123 kDa. As análises da hemolinfa de operárias mostraram que a secreção de vitelogenina varia de acordo com a idade, com picos de produção entre os 20 e 60 dias de idade e cessando por volta dos 100 dias. Essa variação mostra uma relação com as diferentes atividades exercidas pelas operárias na colônia, sugerindo que a vitelogenina pode ter uma importante função na manutenção do polietismo etário em E. tuberculatum. As análises também mostraram que aplicação de HJ III reduz a síntese de vitelogenina no corpo gorduroso, assim como reduz os níveis de vitelogenina circulante na hemolinfa. Esses dados mostram que o HJ regula a produção de vitelogenina em operárias, sugerindo que em operárias adultas de E. tuberculatum o hormônio juvenil não tem função de gonadotropina. / Workers of the ant Ectatomma tuberculatum (Ectatomminae) have active ovaries and lay eggs that are eaten by the queen and larvae (trophic eggs). Vitellogenins are the main proteins found in the eggs of insects and are a source of nutrients to embryo and adults. In social insects, the vitellogenin levels vary between the castes and influences the reproductive social status, nursing and foraging activities, longevity, somatic maintenance and immunity. In most of the insects, the vitellogenin synthesis is regulated mainly by juvenile hormone. However, in non-reproductive worker ants this relationship is poorly characterized. The aims of this study were to characterize the period of vitellogenin secretion in workers of E. tuberculatum and to verify the effects of juvenile hormone application in vitellogenin synthesis. The vitellogenin was identified from queen and worker eggs by SDS-PAGE. Anti-vitellogenin antibodies were obtained and used to detect this protein in the fat body and haemolymph of workers at different ages. Also, juvenile hormone III was applied topically in workers and their effect on vitellogenin synthesis in the fat body and vitellogenin levels in the haemolymph were analyzed by quantitative real time PCR and ELISA. Vitellogenin from E. tuberculatum consists of two polypeptides of 31 and 156 kDa. In the eggs of queens, the 156 kDa polypeptide is cleaved into two subunits of 36 and 123 kDa. The analysis of the haemolymph of workers showed that the secretion of vitellogenin varies with age. The secretion is initiated around the fifth day after emergence, with peak production from days 20 to 60, and stops around day 100. The analyses also showed that juvenile hormone down regulates the vitellogenin mRNA expression and protein synthesis in the fat body, and reduces the vitellogenin levels in the haemolymph. Our data showed that vitellogenin may have an important role in maintaining age polyethism and its synthesis is down regulated by juvenile hormone in E. tuberculatum.