Symbiont-mediated feminization imposes unavoidable host fitness costs

Area of Science:

• Evolutionary biology
• Microbial ecology
• Genetics

Background:

• Maternally inherited bacterial endosymbionts, like Wolbachia, are prevalent in arthropods.
• Some endosymbionts manipulate host reproduction, often by increasing female offspring production, despite potential fitness costs.
• Feminization, where symbionts convert genetic males into females, has been observed in specific sex determination systems.

Purpose of the Study:

• To investigate the fitness costs associated with feminization by Wolbachia in the spider Mermessus fradeorum.
• To determine if co-infecting symbionts influence these fitness costs.
• To explore the implications of feminization costs in XX/X0 sex determination systems.

Main Methods:

• Assessing female fecundity and offspring development in spiders with varying symbiont co-infections.
• Comparing egg counts and developmental success across different symbiotypes, including those with feminizing Wolbachia.
• Utilizing a series of controlled co-infections to isolate the effects of specific symbionts.

Main Results:

• Feminizing Wolbachia significantly reduced egg count by 16% and increased egg developmental failure to 20%.
• Other non-feminizing bacterial endosymbionts did not impose similar fitness costs.
• Fitness costs were specifically linked to the feminizing Wolbachia, not other co-infecting symbionts.

Conclusions:

• Feminizing Wolbachia imposes significant fitness costs on Mermessus fradeorum, primarily through reduced egg viability.
• These costs are likely due to the production of inviable zygotes in the XX/X0 sex determination system.
• The observed fitness costs may restrict the geographic distribution and prevalence of feminization as a reproductive manipulation strategy.