ENVIRONMENTAL-EFFECTS ON CYTOPLASMIC INCOMPATIBILITY AND BACTERIAL LOAD IN WOLBACHIA-INFECTED DROSOPHILA-SIMULANS

The effects of high temperatures, antibiotics, nutrition and larval de nsity on cytoplasmic incompatibility caused by a Wolbachia infection w ere investigated in Drosophila simulans. Exposure of larvae from an in fected stock to moderate doses of tetracycline led to complete incompa tibility when treated females were crossed to infected males; the same doses only caused a partial restoration of compatibility when treated males were crossed to uninfected females. In crosses with treated fem ales, there was a strong correlation between dose effects on hatch rat es and infection levels in embryos produced by these females. Ageing a nd rearing males at a high temperature led to increased compatibility. However, exposing infected females to a high temperature did not infl uence their compatibility with infected males. Male temperature effect s depended on conditions experienced at the larval stage but not the p upal stage. Exposure to 25 degrees C reduced the density of Wolbachia in embryos compared with a 19 degrees C treatment. Low levels of nutri tion led to increased compatibility, but no effect of larval crowding was detected. These findings show the ways environmental factors can i nfluence the expression of cytoplasmic incompatibility and suggest tha t environmental effects may be mediated by bacterial density.