Non-ovarian Wolbachia pipientis titer correlates with fertility rescue of a Drosophila melanogaster bag of marbles hypomorph

Abstract

Bag of marbles ( bam ) is an essential gene that regulates germline stem cell maintenance and germline stem cell daughter cell differentiation in Drosophila melanogaster . When bam is partially functional (hypomorphic), the introduction of Wolbachia pipientis rescues the mutant fertility phenotype that would otherwise result in partial sterility. Infection by different W. pipientis variants results in differential rescue of the bam hypomorph fertility phenotype. We were intrigued by the varying degrees of rescue exhibited in the bam hypomorph when exposed to different W. pipientis variants, prompting us to investigate whether this phenomenon is attributable to variations in the titers of W. pipientis variants. We found no significant difference in ovarian titer between two W. pipientis variant groups, w Mel-like (low bam hypomorph fertility rescue) and w MelCS-like variants (higher bam hypomorph fertility rescue), at bam hypomorph peak fertility. However, carcass (whole flies without the ovaries) titer between w Mel-like and w MelCS-like infected bam hypomorph differed during peak fertility rescue. A positive correlation emerged between the combined titers of ovarian and carcass infections and fertility, implying a more extensive influence that extends beyond ovarian infection alone.

Figure 1. Absolute quantification of W. pipientis titers in female flies shows that both ovarian and carcass W. pipientis titer have a positive correlation with fertility.

W. pipientis titer in female (A) WT and (B) bam hypomorph D. melanogaster ovaries calculated using absolute quantification qPCR. P < 0.05 is specified at a given age/mating status if there is a significant difference between w Mel-like and w MelCS-like variant titer (linear regression model, R). (C) Ovarian and carcass W. pipientis titer during bam hypomorph peak fertility rescue (six-day old). P < 0.05 in the legend designates that there is a significant difference in w Mel-like and w MelCS-like W. pipientis carcass titer while there are no significant differences (NS = Not significant) in the ovaries (linear regression model, R). P < 0.05 or NS is indicated between carcass and ovarian W. pipientis variant titer (Two-Way ANOVA, R). (D) The correlation between D. melanogaster fertility and W. pipientis (all variant titer combined) ovarian and carcass titer. P < 0.05 is indicated in the legend to represent a statistically significant correlation between fertility and W. pipientis in both the ovaries and carcass (linear regression model, R). NS between the linear regression lines indicates no statistically significant difference between slopes.