Sodalis glossinidius, a maternally inherited secondary symbiont of the tsetse fly, is a bacterium in the early/intermediate state of the transition toward symbiosis, representing an important model for investigating establishment and evolution of insect–bacteria symbiosis. The absence of phylogenetic congruence in tsetse-Sodalis coevolution and the existence of Sodalis genotypic diversity in field flies are suggestive for a horizontal transmission route. However, to date no natural mechanism for the horizontal transfer of this symbiont has been identified. Using novel methodologies for the stable fluorescent-labeling and introduction of modified Sodalis in tsetse flies, we unambiguously show that male-borne Sodalis is 1) horizontally transferred to females during mating and 2) subsequently vertically transmitted to the progeny, that is, paternal transmission. This mixed mode of transmission has major consequences regarding Sodalis’ genome evolution as it can lead to coinfections creating opportunities for lateral gene transfer which in turn could affect the interaction with the tsetse host.

No abstract

Les auteurs décrivent une technique améliorée de dissection de l'intestin moyen et des glandes salivaires des glossines. En ajoutant à la dissection le proventricule, la méthode permet d'obtenir un tableau plus complet du développement des trypanosomes chez la mouche infectée.

Pupae and teneral flies of Glossina palpalis gambiensis originating from three successive reproductive cycles were compared for their size and weight. In general, pupal weight and fly weight increased, whereas fly size, measured as wing vein length, decreased with the number of reproductive cycles. The linear regression observed between weight and wing vein length of the fly demonstrated that, particularly for flies originating from the first and second larvipositions, small changes in wing vein length reflected substantial differences in weight. The results of these laboratory experiments were compared with some field data on Glossina morsitans from Zambia and related literature. The life span of the female tsetse, affecting the size of her progeny, could clarify partially some of the field observed seasonal changes in size, whereas the correlation between fly size and weight could eventually explain the differential mortality of some size classes of tsetse flies. However, whether these laboratory observations can be extrapolated to the field has still to be confirmed.

Sur 440 mouches ténérales de Glossina palpalis gambiensis nourries une fois sur cobaye infecté chroniquement avec Trypanosoma brucei brucei EATRO 1125, le taux d'infection procyclique s'élève à 2,32 %, tandis que celui de l'infection métacyclique est de 11,29 %, dont 13,19 % chez les mâles et 9,55 % chez les femelles. Aucune différence significative sur la capacité vectorielle n'est observée entre les mâles et les femelles. Le degré de la parasitémie et le pourcentage des formes courtes au moment du repas infectant, combinés aux conditions de maintenance, semblent influencer l'infection chez les mouches.