Male rearing temperature affects cytoplasmic incompatibility by Rickettsiella bacteria

Bacterial endosymbionts manipulate reproduction in arthropod host species to increase infection rate. One such manipulation is cytoplasmic incompatibility (CI), wherein uninfected females produce infertile eggs when mated with infected males. In the spider Mermessus fradeorum (Linyphiidae), a bacterial symbiont in the genus Rickettsiella causes variable levels of CI. We hypothesized that male development time affects CI strength in M. fradeorum. I changed development rate of Rickettsiella-infected spiders by manipulating both temperature (20°C vs 26°C) and feeding (a fly every 4 vs 10 days). Average development time increased by 9 days with lower temperatures, 20 days with lower feed, and 27 days with both, relative to high feed and temperature. Males were mated with uninfected females to test CI strength, and then to infected females as a control, and egg hatch rate determined via egg mass dissections. I found that hatch rate of compatible crosses (both infected) was uniformly high (0.992 ± 0.005) and significantly higher than incompatible crosses (infected and uninfected) (0.274 ± 0.036). Among incompatible crosses, hatch rate was 2.15x higher for offspring of higher temperature males than lower temperature males (P=0.0011). Male feeding was not significantly associated with hatch rate, indicating temperature, rather than simply developmental rate, influenced CI strength. However, hatch rate across all incompatible crosses remained highly variable, implying additional factors influence symbionts’ effectiveness at inducing CI. Results suggest that symbiotic manipulation is quite sensitive to environmental conditions in this system.