*Article* **Life History Traits in Two** *Drosophila* **Species Differently Affected by Microbiota Diversity under Lead Exposure**

**Mirjana Beribaka 1,\* , Mihailo Jeli´c <sup>2</sup> , Marija Tanaskovi´c <sup>3</sup> , Cvijeta Lazi´c <sup>1</sup> and Marina Stamenkovi´c-Radak <sup>2</sup>**


**Simple Summary:** Microbiota have a significant functional role in the life of the host, including immunity, lifespan and reproduction. *Drosophila* species are attractive model organisms for investigating microbiota diversity from different aspects due to their simple gut microbiota, short generation time and high fertility. Considering such an important role of the microbiota in the life of *Drosophila*, we investigated the extent to which lead (Pb), as one of the most abundant heavy metals in the environment, affects the microbiota and the fitness of this insect host. The results indicate that different factors, such as population origin and sex, may affect individual traits differently and this could be species-specific. In addition, there are members of microbiota that help the host to overcome environmental stress and they could play a key role in reducing the fitness cost in such situations. Studying the influence of microbiota on the adaptive response to heavy metals and the potential implications on overall host fitness is of great pertinence.

**Abstract:** Life history traits determine the persistence and reproduction of each species. Factors that can affect life history traits are numerous and can be of different origin. We investigated the influence of population origin and heavy metal exposure on microbiota diversity and two life history traits, egg-to-adult viability and developmental time, in *Drosophila melanogaster* and *Drosophila subobscura,* grown in the laboratory on a lead (II) acetate-saturated substrate. We used 24 samples, 8 larval and 16 adult samples (two species × two substrates × two populations × two sexes). The composition of microbiota was determined by sequencing (NGS) of the V3–V4 variable regions of the 16S rRNA gene. The population origin showed a significant influence on life history traits, though each trait in the two species was affected differentially. Reduced viability in *D. melanogaster* could be a cost of fast development, decrease in *Lactobacillus* abundance and the presence of *Wolbachia*. The heavy metal exposure in *D. subobscura* caused shifts in developmental time but maintained the egg-to-adult viability at a similar level. Microbiota diversity indicated that the *Komagataeibacter* could be a valuable member of *D. subobscura* microbiota in overcoming the environmental stress. Research on the impact of microbiota on the adaptive response to heavy metals and consequently the potential tradeoffs among different life history traits is of great importance in evolutionary research.

**Keywords:** *Drosophila melanogaster*; *Drosophila subobscura*; egg-to-adult viability; developmental time; microbiota diversity; lead exposure
