Rode, N. | bioRxiv Science

bioRxiv2026

Core Bacterial and Host Fruit-Specific Yeast Microbiota in a Polyphagous Fly Pest

Holometabolous polyphagous insects undergo metamorphosis and exploit multiple host plants, exposing them to highly variable ecological conditions across both life stages and host plants. Whether these insects harbour a stable core microbiota, a life stage- or a host plant-specific microbiota remain open questions. Here, we characterised fungal and bacterial communities associated with Drosophila suzukii across life stages (larvae, pupae and emerging flies) and host fruits (cherry, blackberry and strawberry) using 16S and ITS metabarcoding. We tested the relative influence of life stage and host fruit on microbiota composition using community and network-based analyses. First, we identified that yeasts, but not bacteria, were strongly structured among host fruits. Bacteria and filamentous fungi were shared across fruits, constituting a fruit core microbiota dominated by Gluconobacter cerinus, Tatumella sp. and Cladosporium spp. In contrast, yeast were rather fruit-specific: Hanseniaspora and Pichia genera mostly associated with cherries and strawberries, contrary to Metschnikowia with blackberries. Second, we found that fungal, but not bacterial, communities of D. suzukii were structured among host fruits. D. suzukii harboured a core bacterial microbiota composed of G. cerinus and a niche-specific (host plant-specific) microbiota composed of yeasts: Hanseniaspora typical in individuals related to cherry and strawberry, and Metschnikowia to blackberry. We also verified that individuals from artificial laboratory infestations and natural field infestations harboured similar microbial communities when they developed under the same laboratory conditions. Components of both core and niche-specific microbiota were most likely horizontally acquired by D. suzukii from host fruits. Taken together our results underline the importance of metacommunity approaches to investigate tripartite interactions among insects, host plants and microbiota.

ecology↗

bioRxiv2018

Estimating the fitness effect of deleterious mutations during the two phases of the life cycle: a new method applied to the root-rot fungus Heterobasidion parviporum

Many eukaryote species including taxa such as fungi or algae have a lifecycle with substantial haploid and diploid phases. A recent theoretical model predicts that such haploid-diploid lifecycles are stable over long evolutionary time scales when segregating deleterious mutations have stronger effects in homozygous diploids than in haploids and when they are partially recessive in heterozygous diploids. The model predicts that effective dominance, a measure that accounts for these two effects, should be close to 0.5 in these species. It also predicts that diploids should have higher fitness than haploids on average. However, an appropriate statistical framework to conjointly investigate these predictions is currently lacking. In this study, we derive a new quantitative genetic model to test these predictions using fitness data of two haploid parents and their diploid offspring and genome-wide genetic distance between haploid parents. We apply this model to the root-rot basidiomycete fungus Heterobasidion parviporum, a species where the heterokaryotic (equivalent to the diploid) phase is longer than the homokaryotic (haploid) phase. We measured two fitness-related traits (mycelium growth rate and the ability to degrade wood) in both homokaryons and heterokaryons and we used whole-genome sequencing to estimate nuclear genetic distance between parents. Possibly due to a lack of power, we did not find that deleterious mutations were recessive or more deleterious when expressed during the heterokaryotic phase. Using this model to compare effective dominance among haploid-diploid species where the relative importance of the two phases varies should help better understand the evolution of haploid-diploid life cycles.\n\nArticle summary for Issue HighlightsMany eukaryote species including taxa such as fungi or algae spend a large portion of their life cycle as haploids and as diploids. Clergeot, Rode et al. derive a statistical model to test whether deleterious mutations have stronger effects in homozygous diploids than in haploids, whether they are partially recessive in heterozygous diploids and whether diploids have higher fitness than haploids on average. As an illustration, they use their model to study growth rate and the ability to degrade wood in the root-rot fungus Heterobasidion parviporum. Their model should help gaining further insights into the evolution of haploid-diploid life cycles.

evolutionary biology↗