Leaf-associated bacterial and fungal taxa shifts in response to larvae of the tree hole mosquito, Ochlerotatus triseriatus

Abstract

Larvae of the eastern tree hole mosquito, Ochlerotatus triseriatus (Say), and related container-breeding species are known to feed upon substrate-associated microorganisms. Although the importance of these microbial resources to larval growth has been established, almost nothing is known about the taxonomic composition and dynamics of these critical microbial food sources. We examined bacterial and fungal community compositional changes on oak leaves tethered in natural tree hole habitats of O. triseriatus. We eliminated larvae experimentally in a subset of the tree holes and examined 16S rDNA gene sequences for bacteria and ergosterol concentrations and 18S rRNA gene sequences for fungi collected from leaf material subsamples. Leaf ergosterol content varied significantly with time, but not treatment. Principal component analysis (PCA) was used to compare microbial taxonomic patterns found in leaves incubated with or without larvae present, and we found that larval presence affected both bacterial and fungal groups, either from loosely attached or strongly adherent categories. Bacterial communities generally grouped more tightly when larvae were present, and class level taxa proportions changed when larvae were present, suggesting selection by larval feeding or activities for particular taxa such as members of the Bacteroidetes, Alphaproteobacteria, and Betaproteobacteria classes. Fungal taxa composite scores also separated along PC axes related to the presence of larvae and indicated larval feeding effects on several higher taxonomic groups, including Saccharomycetes, Dothideomycetes, and Chytridiomycota. These results support the hypothesis that larval mosquito feeding and activities altered microbial communities associated with substrate surfaces, potentially leading to decreased food value of the resource and affecting decomposition of particulate matter in the system.

Figure 1

Ergosterol concentrations in tree hole leaf material during the experiment

Figure 2

Principal component analysis of bacterial 16S rRNA gene sequence classifications at the class level (or above) for loosely attached and adherent fractions. PC 1–3 explained 85 and 77% of the overall variance for loosely attached and adherent fractions, respectively

Figure 3

Percentage of bacterial 16S rRNA gene sequences in class level (or above) taxonomic categories from loosely attached leaf fraction for composite samples and individual replicates (mean±SE, n=6)

Figure 4

Percentage of bacterial 16S rRNA gene sequences in class level (or above) taxonomic categories from adherent leaf fraction for composite samples and individual replicates (mean±SE, n=6)

Figure 5

Principal component analysis of fungal 18S rRNA gene sequence classifications at the class level for loosely attached and adherent fractions. PC 1–3 explained 79 and 83% of the variance for loosely attached and adherent fractions, respectively

Figure 6

Percentage of fungal 18S rRNA gene sequences in class level (or above) taxonomic categories from the loosely attached leaf fraction for composite samples and individual replicates (mean±SE, n=6)

Figure 7

Percentage of fungal 18S rRNA gene sequences in class level (or above) taxonomic categories from the adherent leaf fraction for composite samples and individual replicates (mean±SE, n=6)