Down but not out: Tracking the transgenerational effects of thermal stress on Wolbachia-induced feminization in an agricultural spider

Many arthropods are infected with maternally-transmitted endosymbionts that manipulate host reproduction to favor infected females. Heritable symbionts are often susceptible to thermal stress, which reduces symbiont titer, transmission rate, and manipulation efficacy. These effects may extend across multiple host generations depending on symbiont recovery time. Here we explored the transgenerational effects of temperature stress on the heritable symbiont community of the dwarf spider Mermessus fradeorum. This spider is infected with several symbionts, including a feminizing strain of Wolbachia that turns genetic males into phenotypic females. We tested the effect of warm temperatures on feminization by exposing spiders to either cool (20°C) or warm (28°C) temperatures throughout their development. Upon reaching adulthood experimental females were propagated for two additional generations at 20°C to track the recovery of Wolbachia and the feminization phenotype across multiple generations. We found that initial exposure to warm temperatures did not affect feminization; however, feminization was reduced in the generation following heat exposure. Feminization recovered two generations removed from heat exposure in spiders that retained Wolbachia; however, several spider lineages lost Wolbachia and hence permanently lost the feminization phenotype. Our findings suggest that thermal stress can have transgenerational effects on heritable symbioses. While heritable symbionts can recover from this disruption, it may take multiple host generations for the symbiosis to fully restabilize. These results will inform future work further characterizing the effect of climactic factors on symbiosis stability.