Microbiota acquisition and transmission in Drosophila flies

Abstract

Understanding the ecological and evolutionary dynamics of host-microbiota associations notably involves exploring how members of the microbiota assemble and whether they are transmitted along host generations. Here, we investigate the larval acquisition of facultative bacterial and yeast symbionts of Drosophila melanogaster and Drosophila suzukii in ecologically realistic setups. Fly mothers and fruit were major sources of symbionts. Microorganisms associated with adult males also contributed to larval microbiota, mostly in D. melanogaster. Yeasts acquired at the larval stage maintained through metamorphosis, adult life, and were transmitted to offspring. All these observations varied widely among microbial strains, suggesting they have different transmission strategies among fruits and insects. Our approach shows microbiota members of insects can be acquired from a diversity of sources and highlights the compound nature of microbiotas. Such microbial transmission events along generations should favor the evolution of mutualistic interactions and enable microbiota-mediated local adaptation of the insect host.

Keywords: Ecology; Microbiome; Model organism.

Graphical abstract

Figure 1

Drosophila larvae associated with maternal microorganisms and fruit microorganisms (A) Experimental setup. A mature female associated with a certain bacteria-yeast assemblage (Com. 1) was left to oviposit on a blueberry inoculated with a different bacteria-yeast assemblage (Com. 2). Fruits presented to D. melanogaster were wounded near the peduncle insertion, not in the case of D. suzukii. (B) Origin of the microorganisms associated with the larvae (% larval samples). (C) Proportion of microorganisms associated with mothers or fruit acquired by larvae among fly and microorganism species (% larval samples). Black dots indicate overall mean and 95% CI per Drosophila species (i.e., independent of microorganism species) while open symbols and related bars indicate mean and 95% CI for each microorganism (independently of the identity of the co-inoculated microorganism and the identity of their competitors in the experimental system; sample sizes n are given in Table S9). Confidence intervals were calculated using normal approximation method.

Figure 2

Drosophila larvae associated with microorganisms from adult males (A) Experimental setup. A mature male and a mature female associated with two different bacteria-yeast assemblages (Com. 1 and Com. 2) were released in a cage that contained a blueberry inoculated with a third bacteria-yeast assemblage (Com. 3). Fruits presented to D. melanogaster were wounded near the peduncle insertion, not in the case of D. suzukii. (B) Origin of the microorganisms associated with the larvae (% larval samples). (C) Proportion of microorganisms associated with males, mothers, or fruit acquired by larvae among fly and microorganism species (% larval samples). Black dots indicate overall mean and 95% CI per Drosophila species (i.e., independent of microorganism species) while open symbols and related bars indicate mean and 95% CI for each microorganism (independently of the identity of the co-inoculated microorganism and the identity of their competitors in the experimental system; sample sizes n are given in Table S9). Confidence intervals were calculated using normal approximation method. The asterisk “∗” indicates a significant difference (α = 0.05, generalized linear mixed model with binomial distribution and logit link function).

Figure 3

Larvae-associated yeasts persisted through Drosophila life cycle and over generations (A) Schematic of the experimental setup. (B) Maintenance of yeasts through Drosophila metamorphosis among fly and yeast species (% young adult samples). (C) Presence of larvae-associated yeasts and acquisition of environmental yeasts in mature adults among fly and yeast species (% mature adult samples). (D) Transmission of the different adult-associated yeasts to a new D. melanogaster generation (% larval samples). In Figures (A), (B), and (C), black dots indicate overall mean and 95% CI per Drosophila species (i.e., independently of the yeast species and the fly sex) while open symbols and related bars indicate mean and 95% CI for each yeast (independently of the identity of the other yeast(s) inoculated in the experimental system; sample sizes n are given in Table S9). Confidence intervals were calculated using normal approximation method.