Abstract
Drosophila melanogaster adults and larvae, but especially larvae, had profound effects on the densities and community structure of yeasts that developed in banana fruits. Pieces of fruit exposed to adult female flies previously fed fly-conditioned bananas developed higher yeast densities than pieces of the same fruits that were not exposed to flies, supporting previous suggestions that adult Drosophila vector yeasts to new substrates. However, larvae alone had dramatic effects on yeast density and species composition. When yeast densities were compared in pieces of the same fruits assigned to different treatments, fruits that developed low yeast densities in the absence of flies developed significantly higher yeast densities when exposed to larvae. Across all of the fruits, larvae regulated yeast densities within narrow limits, as compared to a much wider range of yeast densities that developed in pieces of the same fruits not exposed to flies. Larvae also affected yeast species composition, dramatically reducing species diversity across fruits, reducing variation in yeast communities from one fruit to the next (beta diversity), and encouraging the consistent development of a yeast community composed of three species of yeast (Candida californica, C. zemplinina, and Pichia kluvyeri), all of which were palatable to larvae. Larvae excreted viable cells of these three yeast species in their fecal pools, and discouraged the growth of filamentous fungi, processes which may have contributed to their effects on the yeast communities in banana fruits. These and other findings suggest that D. melanogaster adults and their larval offspring together engage in ‘niche construction’, facilitating a predictable microbial environment in the fruit substrates in which the larvae live and develop.
Highlights
Many insects consume yeasts, and over the years, many researchers have investigated the effects of dietary yeasts on the growth, fecundity and survival of a wide array of insects
Adult flies emerged from all 11 pieces of banana that were exposed to mated females and monitored for two weeks (M14 treatment group: mean = 21.7, S.D. = 12.1 flies per piece), confirming that our experimental protocol was suitable for rearing Drosophila melanogaster, and implying that viable larvae were present in the mated female, M7 group
We found that the strains of C. californica, C. zemplinina and P. kluyveri isolated from fruits exposed to both adults and larvae in Experiment 2 were highly palatable to young larvae
Summary
Over the years, many researchers have investigated the effects of dietary yeasts on the growth, fecundity and survival of a wide array of insects (reviews in [1], [2]). Insects might have a variety of other effects on yeast communities, as a result of transporting other microbes to new substrates, depositing their waste products on substrates, physically altering the structure of substrates, or other processes that encourage and discourage the growth and survival of particular species of yeasts [2], [3]. Several specialized insect yeast-farmers are known to reduce yeast species diversity and encourage the growth of palatable species of yeasts within the zone of cultivation. With the exception of a handful of species that engage in advanced forms of yeast-farming, there is little evidence that insects promote the growth and maintenance of particular yeast communities in breeding substrates
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