Warm temperature impedes the spread of a heritable manipulative symbiont community in spider populations

Heritable bacterial symbionts commonly manipulate reproduction within arthropod populations for their own benefit. Co-infections of these symbionts can facilitate their dissemination, but extreme temperatures can disrupt these communities, especially when symbionts differ in their temperature tolerance. Researchers conducted a five-generation experiment to investigate how warm temperatures (29°C) affected the spread of symbionts in the spider species Mermessus fradeorum.

Two common infection scenarios were tested: one with a single Rickettsiella infection or a combined feminizing Wolbachia, Rickettsiella, and two other potential "hitchhiker" Wolbachia strains. The study evaluated infection rates in populations heated to either cool (21°C) or warm (29°C) temperatures over multiple spider generations.

At the cooler temperature, Wolbachia feminization caused co-infections in 88% of the hosts, while Rickettsiella-driven cytoplasmic incompatibility (CI) resulted in 83% of infected spiders. All symbionts exhibited high vertical transmission rates (97-99%) and effective hitchhiking. Under warmer conditions, the efficacy of both feminization and CI decreased, and vertical transmission of the symbionts diminished.

The co-infecting symbiont consortium was ultimately eliminated by the warmer temperatures, hindering symbiont transmission. On an individual basis, however, Rickettsiella persisted at reduced CI strength. The study suggests that the competing pressures between the feminizing spread of the symbiont consortium and the environmental-driven decline of symbiont function and transmission could account for the observed patterns of mixed infections in the field populations of this spider.