Breeding site microbiota and oviposition: do female Aedes aegypti shape bacterial communities?

Aedes aegypti , the main vector of multiple arboviruses, is highly associated with human dwellings. Females exhibit an opportunistic oviposition behavior, seldomly laying eggs on natural containers, but rather distributing them among human-generated breeding sites. Bacterial communities associated with such sites, as well as the compositional shifts they undergo through the development of larval stages, have been described. Some bacteria can play a direct role in supporting the success of mosquito development. Additionally, exposure to different bacteria during larval phases can have an impact on life-history traits. Whether the larvae acquire symbionts from aquatic niches, or just require bacteria as food, is still debated. Based on these facts, we hypothesized that female Ae. aegypti shape the bacterial communities of breeding sites during oviposition as a form of niche construction to favor offspring fitness. Our study presents a series of experiments to address whether gravid females modify bacterial consortia present in larval habitats. For this, we first verified if females can mechanically transfer bacteria into culture media. As evidence of mechanical transmission was obtained, we then elaborated an experimental scheme to dissect effects from factors related to the act of oviposition and mosquito-egg-water interactions. The DNA samples obtained from breeding site water aliquots pertaining to five treatments were subjected to amplicon-oriented sequencing to infer their bacterial community structure. Microbial ecology analyses revealed significant differences between treatments in terms of diversity. Particularly, between-treatment shifts in abundance profiles were detected (pairwise PERMANOVA), also showing that females induce a significant decrease in alpha diversity (1-Simpson’s index) through oviposition. In addition, indicator species analysis pinpointed bacterial taxa with significant predicting values and fidelity coefficients for the samples in which single females laid eggs. Furthermore, we provide evidence regarding how one of these indicator taxa, Elizabethkingia , exerts a positive effect upon the development and fitness of mosquito larvae, thus suggesting that the developmental niche construction hypothesis may hold true in this model. survival analysis was performed to assess whether exposure to Asaia or Elizabethkingia affected the duration of larval instars (L1, L2, L3, and L4) and the pupal stage. The total immature development time (L1 to adult) and larval survival were also compared between Ae. aegypti groups using the same approach. Global differences between the control, Asaia, and Elizabethkingia -exposed larvae were tested by the Log-rank test. When significant variation was detected, paired tests were then performed. significance levels were corrected by the Bonferroni criterion. Wing lengths were compared using the Kruskal-Wallis test. Statistical analyses were carried out using R (version 3.2.3). communities of water-holding containers during egg-laying. Our findings showed that the act of oviposition, represented by treatment 5 (T 5 ), significantly decreased the diversity of the bacterial communities present in the breeding sites. As the Simpson index is a dominance metric an uneven microcosm (dominated by the most abundant taxa) could represent an advantageous scenario