Evolution of Drosophila resistance against different pathogens and infection routes entails no detectable maintenance costs.
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.
Instituto Gulbenkian de Ciência, Apartado 14, 2781-901, Oeiras, Portugal.
Vítor G
VG
Faria
Instituto Gulbenkian de Ciência, Apartado 14, 2781-901, Oeiras, Portugal.
Nelson E
NE
Martins
Instituto Gulbenkian de Ciência, Apartado 14, 2781-901, Oeiras, Portugal.
Tânia
T
Paulo
Instituto Gulbenkian de Ciência, Apartado 14, 2781-901, Oeiras, Portugal.
Luís
L
Teixeira
Instituto Gulbenkian de Ciência, Apartado 14, 2781-901, Oeiras, Portugal. esucena@igc.gulbenkian.pt.|Departamento de Biologia Animal, Faculdade de Ciências, Universidade de Lisboa, edifício C2, Campo Grande, 1749-016, Lisboa, Portugal. esucena@igc.gulbenkian.pt.
Élio
É
Sucena
cE3c: Centre for Ecology, Evolution and Environmental Changes, Faculdade de Ciências, Universidade de Lisboa, edifício C2, Campo Grande, 1749-016, Lisboa, Portugal. snmagalhaes@fc.ul.pt.
Sara
S
Magalhães
D000222:Adaptation, Physiological / Q000235:genetics*; D000818:Animals; D005075:Biological Evolution; D060467:Disease Resistance / Q000235:genetics*; D004331:Drosophila melanogaster / Q000235:genetics* / Q000276:immunology; D056084:Genetic Fitness; D007304:Insect Viruses; D007814:Larva; D008018:Life Cycle Stages; D016014:Linear Models; D016016:Proportional Hazards Models; D011549:Pseudomonas; D012641:Selection, Genetic
Costs; Drosophila; experimental evolution; host-parasite; immunity; trade-offs