Stock populations and experimental conditions
The experimental populations were established from a long-term
laboratory population called Ives (IV) that was initiated from about 200
wild D. melanogaster of each sex collected in Massachusetts in
1975 (Charlesworth & Charlesworth, 1985). This population has been
maintained in the lab at high density, with a census size in thousands,
for more than 30 years and is adapted to the laboratory environment
(Houle & Rowe, 2003). In the sexual competition experiment, we also
used a reference population homozygous for a recessive ebonymutation previously backcrossed into the IV stock. To estimate pathogen
virulence during experimental evolution, at each generation we ran a
control using a line homozygous for a recessive relish mutation.
The relish mutation blocks the Imd pathway that plays an
important role in defense against gram negative bacterial pathogens
(Hedengren et al. , 1999)); relish mutants are therefore
highly susceptible to P. entomophila (Vallet-Gely et al. ,
2010).
All flies in the experiment were maintained on fly media composed of
(for 1L water): 6.2g Agar powder (ACROS N. 400400050), 58.8g Farigel
wheat (Westhove N. FMZH1), 58.8g yeast (Springaline BA10), 100ml grape
juice; 4.9ml Propionic acid (Sigma N. P1386), 26.5 ml of Methyl
4-hydroxybenzoate (Nipagin M, VWR N. ALFAA14289.0) solution (400g/l) in
95% ethanol. Populations were kept at 25⁰C with a 12L:12D cycle.