Environmental specificity in Drosophila-bacteria symbiosis affects host developmental plasticity

Abstract

Environmentally acquired microbial symbionts could contribute to host adaptation to local conditions like vertically transmitted symbionts do. This scenario necessitates symbionts to have different effects in different environments. We investigated this idea in Drosophila melanogaster, a species which communities of bacterial symbionts vary greatly among environments. We isolated four bacterial strains isolated from the feces of a D. melanogaster laboratory strain and tested their effects in two conditions: the ancestral environment (i.e. the laboratory medium) and a new environment (i.e. fresh fruit with live yeast). All bacterial effects on larval and adult traits differed among environments, ranging from very beneficial to marginally deleterious. The joint analysis of larval development speed and adult size further shows bacteria affected developmental plasticity more than resource acquisition. This effect was largely driven by the contrasted effects of the bacteria in each environment. Our study illustrates that understanding D. melanogaster symbiotic interactions in the wild will necessitate working in ecologically realistic conditions. Besides, context-dependent effects of symbionts, and their influence on host developmental plasticity, shed light on how environmentally acquired symbionts may contribute to host evolution.

The partitioning of symbionts effects on host resource acquisition and developmental plasticity

“…In these 156 analyses, we used a single data point per combination of yeast treatment, fly population and fly 157 sex. Based on prior work (Guilhot et al 2019), we expected that a negative correlation between 158 these two traits would indicate that yeasts affected mostly host resource allocation ( Figure 2), 159 while a positive would reflect substantial variation in host resource acquisition among the yeast 160 strains. We performed two regression methods: the asymmetrical ordinary least squares 161 regression (OLS), which enables to test differences among fly populations, and the symmetrical 162 orthogonal regression (reported in Supp Mat).…”

“…For example, microbial 39 symbionts affect hosts reproductive strategy along the lifespan -fecundity allocation trade-off 40 in invertebrates (Emelianoff et al 2008;Gould et al 2018;Walters et al 2019) and plants 41 (Gundel et al 2013;Yule, Miller and Rudgers 2013;Chung, Miller and Rudgers 2015). For 42 instance, we recently reported bacterial symbionts of Drosophila melanogaster that also affect 43 host developmental plasticity along the trade-off between speed of larval development and adult 44 size (Guilhot et al 2019). Other microbial symbionts mainly vary in their effects on host 45 resource acquisition.…”

Bacterial influence on the maintenance of symbiotic yeast through Drosophila metamorphosis

“…However, the analysis of larval survival revealed no significant effect of the bacteria on this 143 trait (Guilhot et al, 2019).…”

“…Material and methods 61 Biological material 62 We used a Drosophila melanogaster (Meigen, 1830) Oregon-R strain usually maintained on 63 banana medium (233 g.L -1 banana, 62 g.L -1 sugar, 62 g.L -1 dead yeast, 25 g.L -1 ethanol, 10 64 g.L -1 agar and 5 g.L -1 nipagin) at 21°C with a 14 h/10 h day-night cycle. The four bacterial 65 strains used had been isolated from feces of adult Oregon-R flies and had been described in 66 Guilhot et al (2019). Bacterial strains were identified as Staphylococcus sp.…”

“…Colonies of the five microbial symbionts (yeast and bacteria) were distinguished according to 109 their morphology (see Guilhot et al 2019).…”