Fire ant ovary gene expression analyses revealed immune and insulin pathways underlie the reproductive transition from virgin to mated queen.

BACKGROUND: Solenopsis invicta queens experience significant behavioral and physiological changes after mating, which are essential for their reproductive success. We investigated differences in ovary gene expression in virgin alate queens, newly mated queens, and mated queens to identify candidate genes associated with their physiological transition to mature egg-laying queens. Virgin queens and mated queens were obtained from field colonies and newly mated queens were collected from the ground immediately after their mating flight. Whole ovaries of virgin alate queens, and germaria and vitellaria from the ovaries of newly mated and mature mated queens were dissected. Pools of each of these five organs/tissues were used for RNAseq and RT-qPCR analyses.

RESULTS: Principal component analyses revealed a distinct transcriptomic profile among alate virgin ovaries, germaria of newly mated, and germaria of mated queens, highlighting the effect of mating driving significant differences in global gene expression. Mating did not have such a differentiating effect among libraries of newly mated and mated queen vitellaria. Differentially expressed genes (DEGs) were identified between whole ovary transcriptome of virgin alate queens and germaria of newly mated and mated queens, as well as vitellaria of newly mated and mated queens. There were 22 gene ontology terms enriched among the DEGs in the germaria analysis, of note were those enriched in development and phosphorylation. In the vitellarium, terms related to nucleobase-containing molecule processes and fatty acid metabolism were enriched. Sixty-one DEGs were shared between germaria and vitellaria libraries, mainly linked to immunity, lipid metabolism, development, and transcriptional regulation. Phenoloxidase was highly expressed in mated queens in both ovarian regions, suggesting a role in immunity and choriogenesis. Vg3, one S. invicta vitellogenin gene, was upregulated in the vitellaria of mated queens, reinforcing its role in vitellogenesis. Transcripts of the prostaglandin E2 receptor showed ovary region-specific regulation, suggesting a significant role in immunity, oocyte development and potentially in the release of egg-laying behavior. Insulin-related genes were up-regulated in mated queens, reflecting the metabolic demands for egg production.

CONCLUSION: This study advances our understanding of immunity and mating and other key signaling pathways in fire ant reproduction.