Reduced fecundity associated with <i>Wolbachia</i> infection in a Neotropical drosophilid

Abstract Endosymbionts usually develop strategies that can enhance their persistence within host populations. Wolbachia , a prevalent endosymbiont, induces phenotypes that promote its spread, often at the cost of host fitness. However, demonstrating these strategies in laboratory settings can be challenging due to confounding factors, such as antibiotic treatment or number of host lines. A previous study on a single antibiotic‐treated Drosophila sturtevanti line paradoxically found lower fecundity in infected females, even though most females in the population were naturally infected and reproductive phenotypes were expected. Here, we investigate the impact of Wolbachia infection on the fecundity across multiple lines of D. sturtevanti , focusing on whether there is a consistent reduction in fecundity. Additionally, we aim to distinguish the phenotypic effects of Wolbachia infection from those of antibiotic treatment. We dissected a total of 1680 ovaries from females at seven maturity stages across six lines of D. sturtevanti : three naturally infected and three uninfected. Also, all lines underwent antibiotic treatment to assess its impact on fecundity. Our results suggest no difference in fecundity between infected and uninfected lines, indicating that Wolbachia infection does not regulate this trait in the host population. However, antibiotic treatment reduced fecundity across all lines, with a more pronounced decline in infected ones. These findings highlight the inconsistency of antibiotic treatment outcomes and the risk of misinterpreting Wolbachia 's fitness effects when relying on a single treated line. The study emphasizes the need for refined methods and more accurate analyses to assess Wolbachia ‐induced phenotypic diversity.