Drosophila Regulate Yeast Density and Increase Yeast Community Similarity in a Natural Substrate Judy A. Stamps1*, Louie H. Yang 2 , Vanessa M. Morales3, Kyria L. Boundy-Mills4 1 Department of Evolution and Ecology, University of California Davis, Davis, California, United States of America, 2 Department of Entomology, University of California Davis, Davis, California, United States of America, 3 Department of Food Science and Technology, University of California Davis, Davis, California, United States of America, 4 Department of Food Science and Technology, University of California Davis, Davis, California, United States of America 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. Citation: Stamps JA, Yang LH, Morales VM, Boundy-Mills KL (2012) Drosophila Regulate Yeast Density and Increase Yeast Community Similarity in a Natural Substrate. PLoS ONE 7(7): e42238. doi:10.1371/journal.pone.0042238 Editor: Minna-Maarit Kyto¨ viita, Jyva¨skyla¨ University, Finland Received March 26, 2012; Accepted July 4, 2012; Published July 31, 2012 Copyright: 2012 Stamps et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: These authors have no support or funding to report. Competing Interests: The authors have declared that no competing interests exist. * E-mail: jastamps@ucdavis.edu Introduction 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 (reviews in [1], [2]). However, much less is known about the other side of the equation: the effects of insects on yeast communities. Aside from consumption, the most widely reported effect of insects on yeasts is vectoring: adult insects in several taxa transfer viable, palatable yeast cells to new substrates, where the yeast grows and is then eaten by adults or their larvae [1], [2]. But 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]. In other words, insect might engage in niche construction [4], [5], if their actions and metabolic processes support particular yeast commu- nities in the substrates in which they live and feed. 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. For instance, workers of attine ants in the Cyphomyrmex rimosus complex farm cultivars of yeast that belong to a derived, monophyletic clade, and engage in a variety of behaviors that encourage the growth of these yeasts within their nests [6], [7]. However, 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. Drosophila are prime candidates for studies of the effects of insects on yeast communities, because it is already clear that Drosophila both consume and vector yeast. Yeasts are a major source of nutrition for the adults and larvae of most saprophagous Drosophila (Diptera: Drosophilidae) [8], and larval growth and survivorship is affected by the yeast species available to them [8–10]. There are indications that mixed yeast diets confer higher benefits to flies than monocultures, especially when the yeasts and fly larvae are growing on natural substrates [11], [12], and that some yeasts may improve the ability of flies to resist pathogens [13]. Evidence that Drosophila adults vector yeast comes from studies demonstrating that yeasts develop in sterile substrates following visits by adult flies [14], of overlap in species composition between the yeasts collected at fly feeding or breeding sites and the yeasts carried by adult flies (e.g. [15–17]), and experiments demonstrating that yeast commu- nities fail to develop in some natural substrates if flies and other potential animal vectors are physically excluded from them [18]. There are also indications that Drosophila larvae or adults might engage in activities that encourage or discourage the growth of particular species of yeasts, and hence affect yeast community PLoS ONE | www.plosone.org 1 July 2012 | Volume 7 | Issue 7 | e42238