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Drosophila Adaptation to Viral Infection through Defensive Symbiont Evolution

Publication . Paulo, Tânia F.; Nolte, Viola; Schlötterer, Christian; Sucena, Élio; Teixeira, Luis

Microbial symbionts can modulate host interactions with biotic and abiotic factors. Such interactions may affect the evolutionary trajectories of both host and symbiont. Wolbachia protects Drosophila melanogaster against several viral infections and the strength of the protection varies between variants of this endosymbiont. Since Wolbachia is maternally transmitted, its fitness depends on the fitness of its host. Therefore, Wolbachia populations may be under selection when Drosophila is subjected to viral infection. Here we show that in D. melanogaster populations selected for increased survival upon infection with Drosophila C virus there is a strong selection coefficient for specific Wolbachia variants, leading to their fixation. Flies carrying these selected Wolbachia variants have higher survival and fertility upon viral infection when compared to flies with the other variants. These findings demonstrate how the interaction of a host with pathogens shapes the genetic composition of symbiont populations. Furthermore, host adaptation can result from the evolution of its symbionts, with host and symbiont functioning as a single evolutionary unit.

2016-09-29Journal article

Open access

Testing cannibalism as a mechanism for horizontal transmission of Wolbachia in Drosophila

Publication . Faria, Vitor G.; Paulo, Tânia F.; Sucena, Élio

Wolbachia are intracellular symbionts of many species of animals, mostly arthropods. Vertical transmission of Wolbachia is exclusively maternal and this endobacterium promotes reproductive manipulations of its hosts, increasing the fitness of infected females. Moreover, Wolbachia provides its hosts with a wide range of adaptive features ranging from protection against viral infections to dietary niche occupancy. Therefore, Wolbachia can potentially contribute to the evolutionary processes of sexual selection and speciation. The horizontal transmission of Wolbachia is strongly suggested by the non-concordant phylogeny of this endosymbiont and that of its hosts. However, the ecological mechanism(s) responsible for endosymbiont transmission between different hosts is still largely unknown. In the present study, we look at ingestion as a possible natural form of Wolbachia horizontal transmission. To this aim, we tested cannibalism between infected and uninfected Drosophila hosts, under different conditions of nutrition and gut integrity. Although ingestion represents a general and incontestable portal of entry for microorganisms, we did not find infection by Wolbachia in the progeny of cannibal individuals fed on infected flies. Our study suggests that if ingestion is a vehicle for horizontal transmission of Wolbachia in nature, either it happens very rarely or it requires other factors or conditions to be effective. We discuss the likeliness of this mechanism with respect to the likelihood of each step necessary for horizontal transmission.

2015-11-03Journal article

Open access

Evolution of Drosophila resistance against different pathogens and infection routes entails no detectable maintenance costs

Publication . Faria, Vítor G.; Martins, Nelson E.; Paulo, Tânia; Teixeira, Luís; Sucena, Élio; Magalhães, Sara

Pathogens exert a strong selective pressure on hosts, entailing host adaptation to infection. This adaptation often affects negatively other fitness-related traits. Such trade-offs may underlie the maintenance of genetic diversity for pathogen resistance. Trade-offs can be tested with experimental evolution of host populations adapting to parasites, using two approaches: (1) measuring changes in immunocompetence in relaxed-selection lines and (2) comparing life-history traits of evolved and control lines in pathogen-free environments. Here, we used both approaches to examine trade-offs in Drosophila melanogaster populations evolving for over 30 generations under infection with Drosophila C Virus or the bacterium Pseudomonas entomophila, the latter through different routes. We find that resistance is maintained after up to 30 generations of relaxed selection. Moreover, no differences in several classical life-history traits between control and evolved populations were found in pathogen-free environments, even under stresses such as desiccation, nutrient limitation, and high densities. Hence, we did not detect any maintenance costs associated with resistance to pathogens. We hypothesize that extremely high selection pressures commonly used lead to the disproportionate expression of costs relative to their actual occurrence in natural systems. Still, the maintenance of genetic variation for pathogen resistance calls for an explanation.

2015-11-17Journal article

Open access

Host adaptation to viruses relies on few genes with different cross-resistance properties

Publication . Martins, N. E.; Faria, V. G.; Nolte, V.; Schlotterer, C.; Teixeira, L.; Sucena, E.; Magalhaes, S.

Host adaptation to one parasite may affect its response to others. However, the genetics of these direct and correlated responses remains poorly studied. The overlap between these responses is instrumental for the understanding of host evolution in multiparasite environments. We determined the genetic and phenotypic changes underlying adaptation of Drosophila melanogaster to Drosophila C virus (DCV). Within 20 generations, flies selected with DCV showed increased survival after DCV infection, but also after cricket paralysis virus (CrPV) and flock house virus (FHV) infection. Whole-genome sequencing identified two regions of significant differentiation among treatments, from which candidate genes were functionally tested with RNAi. Three genes were validated--pastrel, a known DCV-response gene, and two other loci, Ubc-E2H and CG8492. Knockdown of Ubc-E2H and pastrel also led to increased sensitivity to CrPV, whereas knockdown of CG8492 increased susceptibility to FHV infection. Therefore, Drosophila adaptation to DCV relies on few major genes, each with different cross-resistance properties, conferring host resistance to several parasites.

2014-04-22Journal article

Open access