Drosophila regulate yeast density and increase yeast community similarity in a natural substrate

Oviposition Dynamics and Niche Utilization in Two Sympatric Drosophila Species

Many Drosophila species coexist by sharing their feeding and breeding sites, which may influence their oviposition choices in an interspecies social context. Whether and where to lay eggs is a crucial decision for female flies as it influences the success of their offspring, by minimizing the risk of predation, competition, or cannibalism. Significant gaps exist in our understanding of Drosophila oviposition dynamics in co-occurring species. Here we tested oviposition strategies of Drosophila melanogaster and its close relative Drosophila simulans under different conditions, to assess whether a single female would prefer to oviposit separately or together with another female, be it a conspecific or not. We find that ovipositing females, regardless whether they are conspecifics or not, prefer to oviposit at the same site. This might suggest that the flies regard the benefits of sharing oviposition sites as higher than the potential risks of competition or cannibalism. The willingness to share oviposition sites was lower when the nutritional value of the medium was increased by adding yeast, and was lost when flies were allowed to lay the eggs consecutively, instead of being tested together. The latter might be explained by our additional finding that females become attracted by the presence of other females on oviposition substrates and that this attraction is partly driven by visual cues. Ovipositing in groups might facilitate intra- and interspecific social feeding of same age offspring, as well as enrichment of microbes. However, this cooperation dynamic might change if another female's offspring is already present, as it might be perceived as danger of competition or cannibalism.

Shaping the environment - Drosophila suzukii larvae construct their own niche

In holometabolous insects, the choice of oviposition substrate by the adult needs to be coordinated with the developmental needs of the larva. Drosophila suzukii female flies possess an enlarged serrated ovipositor, which has enabled them to conquer the ripening fruit as an oviposition niche. They insert their eggs through the skin of priced small fruits. However, this specialization seems to clash with the nutritional needs for larval development since ripening fruits have a low protein content and are high in sugars. In this work, we studied how D. suzukii larvae develop in and interact with the blueberry. We show that despite its hardness and composition, D. suzukii's first instar larvae are able to use the ripening fruit by engaging in niche construction. They display unique physical and behavioral characteristics that allow them to process the hard-ripening fruit and provoke an improvement in its composition that better suits larval nutritional needs.

The microbiome analysis of ripen grape berries supports the complex etiology of sour rot

Sour rot (SR) is a grapevine disease complex that is not completely understood in its etiology and epidemiology. Recently, SR has received special attention due to its increasing economic importance due to crop losses and reduced wine quality. In this study, the fungal and bacterial microbiota of healthy (i.e., without rot symptoms) and rotten (i.e., exhibiting visual and olfactory SR symptoms) ripe bunches were characterized across 47 epidemics (39 vineyards in six Italian grape-growing areas) over three years. The 16S rRNA gene, ITS high-throughput amplicon sequencing, and quantitative PCR were used to assess the relative abundance and dynamic changes of microorganisms associated with SR. The estimators of genera richness of fungal communities within samples indicated a significantly different diversity between healthy and rotten bunches. For bacterial communities, the healthy and rotten bunches significantly differed in the total number of species, but not in abundance distribution across species. The bunch status (i.e., healthy and rotten) was a significant source of diversity (p < 0.01) when the community composition between samples was evaluated, indicating that microbiome composition varied between healthy and rotten bunches. In particular, healthy and rotten bunches shared 43.1 and 54.8% of fungal and bacterial genera, respectively; 31.3% (fungal) and 26.2% (bacterial) genera were associated with rotten bunches only. The yeast genera Zygosaccharomyces, Zygoascus, Saccharomycopsis, Issatchenkia, and Pichia and the bacterial genera Orbus, Gluconobacter, Komagataeibacter, Gluconacetobacter, and Wolbachia were strongly associated with bunches showing SR symptoms based on a linear discriminant analysis. These microorganisms have been associated with Drosophila insects in literature. The relationships between the microflora associated with SR-affected bunches and the roles of Drosophila in SR development need further investigation, which may open perspectives for more effective disease control.

Sex Pheromone Mediates Resource Partitioning Between Drosophila melanogaster and D. suzukii

The spotted-wing drosophila, Drosophila suzukii and the cosmopolitan vinegar fly D. melanogaster feed on soft fruit and berries and widely overlap in geographic range. The presence of D. melanogaster reduces egg-laying in D. suzukii, possibly because D. melanogaster outcompetes D. suzukii larvae feeding in the same fruit substrate. Flies use pheromones to communicate for mating, but pheromones also serve a role in reproductive isolation between related species. We asked whether a D. melanogaster pheromone also modulates oviposition behaviour in D. suzukii. A dual-choice oviposition assay confirms that D. suzukii lays fewer eggs on blueberries exposed to D. melanogaster flies and further shows that female flies have a stronger effect than male flies. This was corroborated by treating berries with synthetic pheromones. Avoidance of D. suzukii oviposition is mediated by the female D. melanogaster pheromone (Z)-4-undecenal (Z4-11Al). Significantly fewer eggs were laid on berries treated with synthetic Z4-11Al. In comparison, the male pheromone (Z)-11-octadecenyl acetate (cVA) had no effect on D. suzukii oviposition. Z4-11Al is a highly volatile compound that is perceived via olfaction and it is accordingly behaviourally active at a distance from the source. D. suzukii is known to engage in mutual niche construction with the yeast Hanseniaspora uvarum, which strongly attracts flies. Adding Z4-11Al to fermenting H. uvarum significantly decreased D. suzukii flight attraction in a laboratory wind tunnel and a field trapping assay. That a D. melanogaster pheromone regulates oviposition in D. suzukii demonstrates that heterospecific pheromone communication contributes to reproductive isolation and resource partitioning in cognate species. Stimulo-deterrent diversion or push-pull methods, building on combined use of attractant and deterrent compounds, have shown promise for control of D. suzukii. A pheromone that specifically reduces D. suzukii attraction and oviposition adds to the toolbox for D. suzukii integrated management.

Salt concentration in substrate modulates the composition of bacterial and yeast microbiomes of Drosophila melanogaster

Aim: Microbiomes influence the physiology and behavior of multicellular organisms and contribute to their adaptation to changing environmental conditions. However, yeast and bacterial microbiota have usually been studied separately; therefore, the interaction between bacterial and yeast communities in the gut of Drosophila melanogaster (D. melanogaster) is often overlooked. In this study, we investigate the correlation between bacterial and yeast communities in the gut of D. melanogaster. Methods: We studied the shifts in the joint microbiome of Drosophila melanogaster, encompassing both yeasts and bacteria, during adaptation to substrate with varying salt concentrations (0%, 2%, 4%, and 7%) using plating for both yeasts and bacteria and NGS-sequencing of variable 16S rRNA gene regions for bacteria. Results: The microbiome of flies and their substrates was gradually altered at moderate NaCl concentrations (2% and 4% compared with the 0% control) and completely transformed at high salt concentrations (7%). The relative abundance of Acetobacter, potentially beneficial to D. melanogaster, decreased as NaCl concentration increased, whereas the relative abundance of the more halotolerant lactobacilli first increased, peaking at 4% NaCl, and then declined dramatically at 7%. At this salinity level, potentially pathogenic bacteria of the genera Leuconostoc and Providencia were dominant. The yeast microbiome of D. melanogaster also undergoes significant changes with an increase in salt concentration in the substrate. The total yeast abundance undergoes nonlinear changes: it is lowest at 0% salt concentration and highest at 2%-4%. At a 7% concentration, the yeast abundance in flies and their substrate is lower than at 2%-4% but significantly higher than at 0%. Conclusions: The abundance and diversity of bacteria that are potentially beneficial to the flies decreased, while the proportion of potential pathogens, Leuconostoc and Providencia, increased with an increase in salt concentration in the substrate. In samples with a relatively high abundance and/or diversity of yeasts, the corresponding indicators for bacteria were often lowered, and vice versa. This may be due to the greater halotolerance of yeasts compared to bacteria and may also indicate antagonism between these groups of microorganisms.

Identification of key yeast species and microbe-microbe interactions impacting larval growth of Drosophila in the wild

Microbiota consisting of various fungi and bacteria have a significant impact on the physiological functions of the host. However, it is unclear which species are essential to this impact and how they affect the host. This study analyzed and isolated microbes from natural food sources of Drosophila larvae, and investigated their functions. Hanseniaspora uvarum is the predominant yeast responsible for larval growth in the earlier stage of fermentation. As fermentation progresses, Acetobacter orientalis emerges as the key bacterium responsible for larval growth, although yeasts and lactic acid bacteria must coexist along with the bacterium to stabilize this host-bacterial association. By providing nutrients to the larvae in an accessible form, the microbiota contributes to the upregulation of various genes that function in larval cell growth and metabolism. Thus, this study elucidates the key microbial species that support animal growth under microbial transition.

Microbiota acquisition and transmission in Drosophila flies

Understanding the ecological and evolutionary dynamics of host-microbiota associations notably involves exploring how members of the microbiota assemble and whether they are transmitted along host generations. Here, we investigate the larval acquisition of facultative bacterial and yeast symbionts of Drosophila melanogaster and Drosophila suzukii in ecologically realistic setups. Fly mothers and fruit were major sources of symbionts. Microorganisms associated with adult males also contributed to larval microbiota, mostly in D. melanogaster. Yeasts acquired at the larval stage maintained through metamorphosis, adult life, and were transmitted to offspring. All these observations varied widely among microbial strains, suggesting they have different transmission strategies among fruits and insects. Our approach shows microbiota members of insects can be acquired from a diversity of sources and highlights the compound nature of microbiotas. Such microbial transmission events along generations should favor the evolution of mutualistic interactions and enable microbiota-mediated local adaptation of the insect host.

Nutritional Profile and Ecological Interactions of Yeast Symbionts Associated with North American Spruce Beetle (Dendroctonus rufipennis)

To better understand functional ecology of bark beetle-microbial symbioses, we characterized yeast associates of North American spruce beetle (Dendroctous rufipennis Kirby) across populations. Seven yeast species were detected; Wickerhamomyces canadensis (Wickerham) Kurtzman et al. (Sachharomycetales: Saccharomycetaceae) was the most common (74% of isolates) and found in all populations. Isolates of W. canadensis were subsequently tested for competitive interactions with symbiotic (Leptographium abietinum, = Grosmannia abietina) and pathogenic (Beauvaria bassiana) filamentous fungi, and isolates were nutritionally profiled (protein and P content). Exposure to yeast headspace emissions had isolate-dependent effects on colony growth of symbiotic and pathogenic fungi; most isolates of W. canadensis slightly inhibited growth rates of symbiotic (L. abietinum, mean effect: - 4%) and entomopathogenic (B. bassiana, mean effect: - 6%) fungi. However, overall variation was high (range: - 35.4 to + 88.6%) and some yeasts enhanced growth of filamentous fungi whereas others were consistently inhibitory. The volatile 2-phenylethanol was produced by W. canadensis and synthetic 2-phenylethanol reduced growth rates of both L. abietinum and B. bassiana by 36% on average. Mean protein and P content of Wickerhamomyces canadensis cultures were 0.8% and 7.2%, respectively, but isolates varied in nutritional content and protein content was similar to that of host tree phloem. We conclude that W. canadensis is a primary yeast symbiont of D. rufipennis in the Rocky Mountains and emits volatiles that can affect growth of associated microbes. Wickerhamomyces canadensis isolates vary substantially in limiting nutrients (protein and P), but concentrations are less than reported for the symbiotic filamentous fungus L. abietinum.

Transmission of beneficial yeasts accompanies offspring production in Drosophila-An initial evolutionary stage of insect maternal care through manipulation of microbial load?

Parent-to-offspring transmission of beneficial microorganisms is intimately interwoven with the evolution of social behaviors. Ancestral stages of complex sociality-microbe vectoring interrelationships may be characterized by high costs of intensive parental care and hence only a weak link between the transmission of microbial symbionts and offspring production. We investigate the relationship between yeast symbiont transmission and egg-laying, as well as some general factors thought to drive the "farming" of microscopic fungi by the fruit fly Drosophila melanogaster, an insect with no obvious parental care but which is highly dependent on dietary microbes during offspring development. The process of transmitting microbes involves flies ingesting microbes from their previous environment, storing and vectoring them, and finally depositing them to a new environment. This study revealed that fecal materials of adult flies play a significant role in this process, as they contain viable yeast cells that support larval development. During single patch visits, egg-laying female flies transmitted more yeast cells than non-egg-laying females, suggesting that dietary symbiont transmission is not random, but linked to offspring production. The crop, an extension of the foregut, was identified as an organ capable of storing viable yeast cells during travel between egg-laying sites. However, the amount of yeast in the crop reduced rapidly during periods of starvation. Although females starved for 24 h deposited a smaller amount of yeast than those starved for 6 h, the yeast inoculum produced still promoted the development of larval offspring. The results of these experiments suggest that female Drosophila fruit flies have the ability to store and regulate the transfer of microorganisms beneficial to their offspring via the shedding of fecal material. We argue that our observation may represent an initial evolutionary stage of maternal care through the manipulation of microbial load, from which more specialized feedbacks of sociality and microbe management may evolve.

Invasive Drosophila suzukii outnumbers native controphics and causes substantial damage to fruits of forest plants

Impacts of biological invasions are diverse and can have far-reaching consequences for ecosystems. The spotted wing drosophila, Drosophila suzukii, is a major invasive pest of fruits, which negatively affects fruit and wine production. However, little is known about the ecological impact of this fly species on more natural ecosystems it has invaded, such as forests. In this study, we investigated the use of potential host plants by D. suzukii at 64 sites in different forest communities in Switzerland from mid-June to mid-October 2020. We examined more than 12,000 fruits for egg deposits of D. suzukii to assess its direct impact on the plants. We recorded symptoms of fruit decay after egg deposition to determine if D. suzukii attacks trigger fruit decay. In addition, we monitored the drosophilid fauna with cup traps baited with apple cider vinegar, as we expected that D. suzukii would outnumber and potentially outcompete native controphics, especially other drosophilids. Egg deposits of D. suzukii were found on the fruits of 31 of the 39 potential host plant species studied, with 18 species showing an attack rate &gt; 50%. Overall, fruits of Cotoneaster divaricatus (96%), Atropa bella-donna (91%), Rubus fruticosus corylifolius aggr. (91%), Frangula alnus (85%) and Sambucus nigra (83%) were attacked particularly frequently, resulting also in high predicted attack probabilities that varied among forest communities. Later and longer fruiting, black fruit colour, larger fruit size and higher pulp pH all positively affected attack rates. More than 50% of the plant species showed severe symptoms of decay after egg deposition, with higher pulp sugar content leading to more severe symptoms. The high fruit attack rate observed was reflected in a high abundance and dominance of D. suzukii in trap catches, independent of forest community and elevation. Drosophila suzukii was by far the most abundant species, accounting for 86% (81,395 individuals) of all drosophilids. The abundance of D. suzukii was negatively associated with the abundance of the native drosophilids. Our results indicate that the invasive D. suzukii competes strongly with other frugivorous species and that its presence might have far-reaching ecosystem-level consequences. The rapid decay of fruits attacked by D. suzukii leads to a loss of resources and may disrupt seed-dispersal mutualisms through the reduced consumption of fruits by dispersers such as birds.

Black Soldier Fly Larvae Influence Internal and Substrate Bacterial Community Composition Depending on Substrate Type and Larval Density

Saprophagous fly larvae interact with a rich community of bacteria in decomposing organic matter. Larvae of some species, such as the black soldier fly, can process a wide range of organic residual streams into edible insect biomass and thus produce protein as a sustainable component of livestock feed. The microbiological safety of the insects and substrates remains a point of concern. Substrate-associated bacteria can dominate the larval gut microbiota, but the larvae can also alter the bacterial community in the substrate. However, the relative importance of substrate type and larval density in bacterial community dynamics is unknown. We investigated four larval densities (0 [control], 50, 100, or 200 larvae per container [520 mL; diameter, 75 mm]) and three feed substrates (chicken feed, chicken manure, and camelina substrate [50% chicken feed, 50% camelina oilseed press cake]) and sampled the bacterial communities of the substrates and larvae at three time points over 15 days. Although feed substrate was the strongest driver of microbiota composition over time, larval density significantly altered the relative abundances of several common bacterial genera, including potential pathogens, in each substrate and in larvae fed chicken feed. Bacterial communities of the larvae and substrate differed to a higher degree in chicken manure and camelina than in chicken feed. This supports the substrate-dependent impact of black soldier fly larvae on bacteria both within the larvae and in the substrate. This study indicates that substrate composition and larval density can alter bacterial community composition and might be used to improve insect microbiological safety.

IMPORTANCE Black soldier fly larvae can process organic side streams into nutritious insect biomass, yielding a sustainable ingredient of animal feed. In processing such organic residues, the larvae impact the substrate and its microbiota. However, their role relative to the feed substrate in shaping the bacterial community is unknown. This may be important for the waste management industry to determine whether pathogens can be controlled by manipulating the larval density and the timing of harvest. We investigated how the type of feed substrate and the larval density (number of larvae per container) interacted to influence bacterial community composition in the substrates and larvae over time. Substrate type was the strongest driver of bacterial community composition, and the magnitude of the impact of the larvae depended on the substrate type and larval density. Thus, both substrate composition and larval density may be used to improve the microbiological safety of the larvae as animal feed.

Dietary Behavior of Drosophila melanogaster Fed with Genetically-Modified Corn or Roundup®

With the rise in concern about GMOs and pesticides on human health, we have utilized Drosophila melanogaster as a model organism for understanding the effects of Roundup-Ready^® GMO diets on health. We recorded dietary behavior during and after exposure to a medium containing GMO or non-GMO corn, Roundup^® in organic corn medium, and sucrose with or without one of the two Roundup^® formulations. No differences in behavior were observed when Drosophila were exposed to a medium containing Roundup-Ready^® GMO or non-GMO corn. Drosophila can detect and refrain from eating sucrose containing one Roundup^® formulation, Ready-to-Use, which contains pelargonic acid in addition to glyphosate as an active ingredient. Drosophila exhibited dose-dependent increased consumption of sucrose alone after exposure to a medium containing either Roundup^® formulation. This may indicate that flies eating a medium with Roundup^® eat less and were thus hungrier when then given sucrose solution; that a medium with Roundup^® is more difficult to digest; or that a medium with Roundup^® is less nutritious, as would be the case if nutritionally important microbes grew on control medium, but not one containing Roundup^®.

Influence of bacteria on the maintenance of a yeast during Drosophila melanogaster metamorphosis

Interactions between microorganisms associated with metazoan hosts are emerging as key features of symbiotic systems. Little is known about the role of such interactions on the maintenance of host-microorganism association throughout the host’s life cycle. We studied the influence of extracellular bacteria on the maintenance of a wild isolate of the yeast Saccharomyces cerevisiae through metamorphosis of the fly Drosophila melanogaster reared in fruit. Yeasts maintained through metamorphosis only when larvae were associated with extracellular bacteria isolated from D. melanogaster faeces. One of these isolates, an Enterobacteriaceae, favoured yeast maintenance during metamorphosis. Such bacterial influence on host-yeast association may have consequences for the ecology and evolution of insect-yeast-bacteria symbioses in the wild.

Utilizing Probiotics for the Prevention and Treatment of Gastrointestinal Diseases

Probiotics are heavily advertised to promote a healthy gastrointestinal tract and boost the immune system. This review article summarizes the history and diversity of probiotics, outlines conventional in vitro assays and in vivo models, assesses the pharmacologic effects of probiotic and pharmaceutical co-administration, and the broad impact of clinical probiotic utilization for gastrointestinal disease indications.

Environmental influences on for-mediated oviposition decisions in Drosophila melanogaster

Deciding whether or not to lay an egg on a given substrate is an important task undertaken by females of many arthropods. It involves perceiving the environment (e.g. quality of the substrate, temperature, and humidity), formulating a decision, and then conducting the appropriate behaviours to oviposit. This oviposition site selection (OSS) provides a useful system for studying simple decision-making. OSS in fruit flies, Drosophila melanogaster, is influenced by both genetic and environmental variation. Naturally occurring allelic variation in the foraging gene (for) is known to affect OSS. Given a choice of high- and low-nutrient oviposition substrates, groups of rovers (for^R) are known to lay significantly more of their eggs on low-nutrient sites than sitters (for^s) and sitter mutants (for^s2). Here we ask three questions: (1) Is the role of for in OSS affected by the availability of alternate oviposition sites? (2) Is the role of for in OSS sensitive to the density of ovipositing females? and (3) Does the gustatory sensation of yeast play a role in for-mediated variation in OSS? We find a role of choice and female density in rover/sitter differences in OSS, as well as a role of for in response to glycerol, an indicator of yeast. The role of for in OSS decision-making is complex and multi-faceted and should prove fertile ground for further research into the factors affecting decision-making behaviours.

Ethanol-guided behavior in Drosophila larvae

Chemosensory signals allow vertebrates and invertebrates not only to orient in its environment toward energy-rich food sources to maintain nutrition but also to avoid unpleasant or even poisonous substrates. Ethanol is a substance found in the natural environment of Drosophila melanogaster. Accordingly, D. melanogaster has evolved specific sensory systems, physiological adaptations, and associated behaviors at its larval and adult stage to perceive and process ethanol. To systematically analyze how D. melanogaster larvae respond to naturally occurring ethanol, we examined ethanol-induced behavior in great detail by reevaluating existing approaches and comparing them with new experiments. Using behavioral assays, we confirm that larvae are attracted to different concentrations of ethanol in their environment. This behavior is controlled by olfactory and other environmental cues. It is independent of previous exposure to ethanol in their food. Moreover, moderate, naturally occurring ethanol concentration of 4% results in increased larval fitness. On the contrary, higher concentrations of 10% and 20% ethanol, which rarely or never appear in nature, increase larval mortality. Finally, ethanol also serves as a positive teaching signal in learning and memory and updates valence associated with simultaneously processed odor information. Since information on how larvae perceive and process ethanol at the genetic and neuronal level is limited, the establishment of standardized assays described here is an important step towards their discovery.

Testing the adaptive value of sporulation in budding yeast using experimental evolution

Saccharomyces yeast grow through mitotic cell division, converting resources into biomass. When cells experience starvation, sporulation is initiated and meiosis produces haploid cells inside a protective ascus. The protected spore state does not acquire resources and is partially protected from desiccation, heat, and caustic chemicals. Because cells cannot both be protected and acquire resources simultaneously, committing to sporulation represents a trade-off between current and future reproduction. Recent work has suggested that passaging through insect guts selects for spore formation, as surviving insect ingestion represents a major way that yeasts are vectored to new food sources. We subjected replicate populations from five yeast strains to passaging through insects, and evolved control populations by pipette passaging. We assayed populations for their propensity to sporulate after resource depletion. We found that ancestral domesticated strains produced fewer spores, and all strains evolved increased spore production in response to passaging through flies, but domesticated strains responded less. Exposure to flies led to a more rapid shift to sporulation that was more extreme in wild-derived strains. Our results indicate that insect passaging selects for spore production and suggest that domestication led to genetic canalization of the response to cues in the environment and initiation of sporulation.

Genetic, Physiological, and Industrial Aspects of the Fructophilic Non-Saccharomyces Yeast Species, Starmerella bacillaris

Starmerella bacillaris (synonym Candida zemplinina) is a non-Saccharomyces yeast species, frequently found in enological ecosystems. Peculiar aspects of the genetics and metabolism of this yeast species, as well as potential industrial applications of isolated indigenous S. bacillaris strains worldwide, have recently been explored. In this review, we summarize relevant observations from studies conducted on standard laboratory and indigenous isolated S. bacillaris strains.

Relative contributions of egg-associated and substrate-associated microorganisms to black soldier fly larval performance and microbiota

Larvae of the black soldier fly (BSF) can be used to convert organic waste into insect biomass for animal feed. In this process, they interact with microorganisms originating from the substrate, the insect and the environment. The substrate is the main determinant of the larval gut microbiota composition, but inoculation of the substrate with egg-associated bacteria can improve larval performance. We aimed to quantify the relative importance of substrate-associated and egg-associated microorganisms in BSF larval performance, bacterial abundance and bacterial community composition, when larvae were fed with chicken feed or chicken manure. For this, we inactivated substrate-associated microorganisms by autoclaving, or disinfected BSF eggs. Larval survival, weight and proportion of prepupae were determined on day 15. We collected substrate and larval samples on days 0 and 15 and performed 16S rRNA gene-targeted qPCR and amplicon sequencing. In both chicken feed and chicken manure, egg disinfection did not cause any difference in larval performance or overall microbiota composition. In contrast, in chicken manure, substrate-associated microorganisms increased larval biomass and sterilizing the substrate caused major shifts in microbiota. Thus, substrate-associated microorganisms impact not only larval microbiota but also larval performance, whereas egg-associated microorganisms have a minor role in the densities present.

Maternal and larval niche construction interact to shape development, survival, and population divergence in the dung beetle Onthophagus taurus

Through niche construction, organisms modify their environments in ways that can alter how selection acts on themselves and their offspring. However, the role of niche construction in shaping developmental and evolutionary trajectories, and its importance for population divergences and local adaptation, remains largely unclear. In this study, we manipulated both maternal and larval niche construction and measured the effects on fitness-relevant traits in two rapidly diverging populations of the bull-headed dung beetle, Onthophagus taurus. We find that both types of niche construction enhance adult size, peak larval mass, and pupal mass, which when compromised lead to a synergistic decrease in survival. Furthermore, for one measure, duration of larval development, we find that the two populations have diverged in their reliance on niche construction: larval niche construction appears to buffer against compromised maternal niche construction only in beetles from Western Australia, but not in beetles from the Eastern United States. We discuss our results in the context of rapid adaptation to novel conditions and the role of niche construction therein.

Larval density affects phenotype and surrounding bacterial community without altering gut microbiota in Drosophila melanogaster

Larval crowding represents a complex stressful situation arising from inter-individual competition for time- and space-limited resources. The foraging of a large number of individuals may alter the chemical and bacterial composition of food and in turn affect individual's traits. Here we used Drosophila melanogaster to explore these assumptions. First, we used a wide larval density gradient to investigate the impact of crowding on phenotypical traits. We confirmed that high densities increased development time and pupation height, and decreased viability and body mass. Next, we measured concentrations of common metabolic wastes (ammonia, uric acid) and characterized bacterial communities, both in food and in larvae, for three contrasting larval densities (low, medium and high). Ammonia concentration increased in food from medium and high larval densities, but remained low in larvae regardless of the larval density. Uric acid did not accumulate in food but was detected in larvae. Surprisingly, bacterial composition remained stable in guts of larvae whatever their rearing density, although it drastically changed in the food. Overall, these results indicate that crowding deeply affects individuals, and also their abiotic and biotic surroundings. Environmental bacterial communities likely adapt to altered nutritional situations resulting from crowding, putatively acting as scavengers of larval metabolic wastes.

The Microbiota and Gut-Related Disorders: Insights from Animal Models

Over the past decade, the scientific committee has called for broadening our horizons in understanding host–microbe interactions and infectious disease progression. Owing to the fact that the human gut harbors trillions of microbes that exhibit various roles including the production of vitamins, absorption of nutrients, pathogen displacement, and development of the host immune system, particular attention has been given to the use of germ-free (GF) animal models in unraveling the effect of the gut microbiota on the physiology and pathophysiology of the host. In this review, we discuss common methods used to generate GF fruit fly, zebrafish, and mice model systems and highlight the use of these GF model organisms in addressing the role of gut-microbiota in gut-related disorders (metabolic diseases, inflammatory bowel disease, and cancer), and in activating host defense mechanisms and amending pathogenic virulence.

Fruit host-dependent fungal communities in the microbiome of wild Queensland fruit fly larvae

Bactrocera tryoni (Froggatt), the Queensland fruit fly (Qfly), is a highly polyphagous tephritid fly that is widespread in Eastern Australia. Qfly physiology is closely linked with its fungal associates, with particular relationship between Qfly nutrition and yeast or yeast-like fungi. Despite animal-associated fungi typically occurring in multi-species communities, Qfly studies have predominately involved the culture and characterisation of single fungal isolates. Further, only two studies have investigated the fungal communities associated with Qfly, and both have used culture-dependant techniques that overlook non-culturable fungi and hence under-represent, and provide a biased interpretation of, the overall fungal community. In order to explore a potentially hidden fungal diversity and complexity within the Qfly mycobiome, we used culture-independent, high-throughput Illumina sequencing techniques to comprehensively, and holistically characterized the fungal community of Qfly larvae and overcome the culture bias. We collected larvae from a range of fruit hosts along the east coast of Australia, and all had a mycobiome dominated by ascomycetes. The most abundant fungal taxa belonged to the genera Pichia (43%), Candida (20%), Hanseniaspora (10%), Zygosaccharomyces (11%) and Penicillium (7%). We also characterized the fungal communities of fruit hosts, and found a strong degree of overlap between larvae and fruit host communities, suggesting that these communities are intimately inter-connected. Our data suggests that larval fungal communities are acquired from surrounding fruit flesh. It is likely that the physiological benefits of Qfly exposure to fungal communities is primarily due to consumption of these fungi, not through syntrophy/symbiosis between fungi and insect ‘host’.

What can a non-eusocial insect tell us about the neural basis of group behaviour?

Group behaviour has been extensively studied in canonically social swarming, shoaling and flocking vertebrates and invertebrates, providing great insight into the behavioural and ecological aspects of group living. However, the search for its neuronal basis is lagging behind. In the natural environment, Drosophila melanogaster, increasingly used as a model to study neuronal circuits and behaviour, spend their lives surrounded by several conspecifics of different stages, as well as heterospecifics. Despite their dynamic multi-organism natural environment, the neuronal basis of social behaviours has been typically studied in dyadic interactions, such as mating or aggression. This review will focus on recent studies regarding how the behaviour of fruit flies can be shaped by the nature of the surrounding group. We argue that the rich social environment of Drosophila melanogaster, its arsenal of neurogenetic tools and the ability to use large sample sizes for detailed quantitative behavioural analysis makes this species ideal for mechanistic studies of group behaviour.

The microbiota of Drosophila suzukii influences the larval development of Drosophila melanogaster

Microorganisms play a central role in the biology of vinegar flies such as Drosophila suzukii and Drosophila melanogaster: serving as a food source to both adults and larvae, and influencing a range of traits including nutrition, behavior, and development. The niches utilized by the fly species partially overlap, as do the microbiota that sustain them, and interactions among these players may drive the development of crop diseases. To learn more about how the microbiota of one species may affect the other, we isolated and identified microbes from field-caught D. suzukii, and then characterized their effects on D. melanogaster larval development time in the laboratory. We found that the D. suzukii microbiota consistently included both yeasts and bacteria. It was dominated by yeasts of the genus Hanseniaspora, and bacteria from the families Acetobacteraceae and Enterobacteriaceae. Raising D. melanogaster under gnotobiotic conditions with each microbial isolate individually, we found that some bacteria promoted larval development relative to axenic conditions, but most did not have a significant effect. In contrast, nearly all the yeasts tested significantly accelerated larval development. The one exception was Starmerella bacillaris, which had the opposite effect: significantly slowing larval developmental rate. We investigated the basis for this effect by examining whether S. bacillaris cells could sustain larval growth, and measuring the survival of S. bacillaris and other yeasts in the larval gut. Our results suggest S. bacillaris is not digested by D. melanogaster and therefore cannot serve as a source of nutrition. These findings have interesting implications for possible interactions between the two Drosophilia species and their microbiota in nature. Overall, we found that microbes isolated from D. suzukii promote D. melanogaster larval development, which is consistent with the model that infestation of fruit by D. suzukii can open up habitat for D. melanogaster. We propose that the microbiome is an important dimension of the ecological interactions between Drosophila species.

Yeasts affect tolerance of Drosophila melanogaster to food substrate with high NaCl concentration

The ability of model animal species, such as Drosophila melanogaster, to adapt quickly to various adverse conditions has been shown in many experimental evolution studies. It is usually assumed by default that such adaptation is due to changes in the gene pool of the studied population of macroorganisms. At the same time, it is known that microbiome can influence biological processes in macroorganisms. In order to assess the possible impact of microbiome on adaptation, we performed an evolutionary experiment in which some D. melanogaster lines were reared on a food substrate with high NaCl concentration while the others were reared on the standard (favourable) substrate. We evaluated the reproductive efficiency of experimental lines on the high salt substrate three years after the experiment started. Our tests confirmed that the lines reared on the salty substrate became more tolerant to high NaCl concentration. Moreover, we found that pre-inoculation of the high salt medium with homogenized salt-tolerant flies tended to improve reproductive efficiency of naïve flies on this medium (compared to pre-inoculation with homogenized control flies). The analysis of yeast microbiome in fly homogenates revealed significant differences in number and species richness of yeasts between salt-tolerant and control lines. We also found that some individual yeast lines extracted from the salt-tolerant flies improved reproductive efficiency of naïve flies on salty substrate (compared to baker's yeast and no yeast controls), whereas the effect of the yeast lines extracted from the control flies tended to be smaller. The yeast Starmerella bacillaris extracted from the salt-tolerant flies showed the strongest positive effect. This yeast is abundant in all salt-tolerant lines, and very rare or absent in all control lines. The results are consistent with the hypothesis that some components of the yeast microbiome of D. melanogaster contribute to to flies' tolerance to food substrate with high NaCl concentration.

Differential Impacts of Yeasts on Feeding Behavior and Development in Larval Drosophila suzukii (Diptera:Drosophilidae)

Larval Drosophila encounter and feed on a diverse microbial community within fruit. In particular, free-living yeast microbes provide a source of dietary protein critical for development. However, successional changes to the fruit microbial community may alter host quality through impacts on relative protein content or yeast community composition. For many species of Drosophila, fitness benefits from yeast feeding vary between individual yeast species, indicating differences in yeast nutritional quality. To better understand these associations, we evaluated how five species of yeast impacted feeding preference and development in larval Drosophila suzukii. Larvae exhibited a strong attraction to the yeast Hanseniaspora uvarum in pairwise yeast feeding assays. However, larvae also performed most poorly on diets containing H. uvarum, a mismatch in preference and performance that suggests differences in yeast nutritional quality are not the primary factor driving larval feeding behavior. Together, these results demonstrate that yeast plays a critical role in D. suzukii’s ecology and that larvae may have developed specific yeast associations. Further inquiry, including systematic comparisons of Drosophila larval yeast associations more broadly, will be necessary to understand patterns of microbial resource use in larvae of D. suzukii and other frugivorous species.

Application of different markers and data-analysis tools to the examination of biodiversity can lead to different results: a case study with Starmerella bacillaris (synonym Candida zemplinina) strains

Starmerella bacillaris (Candida zemplinina) is a genetically heterogeneous species. In this work, the diversity of 41 strains of various origins is examined and compared by the analysis of the length polymorphism of nuclear microsatellites and the RFLP of mitochondrial genomes. The band patterns are analysed with UPGMA, neighbor joining, neighbor net, minimum spanning tree and non-metric MDS algorithms. The results and their comparison to previous analyses demonstrate that different markers and different clustering methods can result in very different groupings of the same strains. The observed differences between the topologies of the dendrograms also indicate that the positions of the strains do not necessarily reflect their real genetic relationships and origins. The possibilities that the differences might be partially due to different sensitivity of the markers to environmental factors (selection pressure) and partially to the different grouping criteria of the algorithms are also discussed.

Brown Rice Vinegar as an Olfactory Field Attractant for Drosophila suzukii (Matsumura) and Zaprionus indianus Gupta (Diptera: Drosophilidae) in Cherimoya in Maui, Hawaii, with Implications for Attractant Specificity between Species and Estimation of Relative Abundance

Drosophila suzukii (Matsumura) is an agricultural pest that has been observed co-infesting soft-skinned fruits with Zaprionus indianus Gupta. The characterization of olfactory preferences by species is a necessary step towards the development of species-specific attractants. Five olfactory attractants were used to survey the populations of two invasive drosophilids in cherimoya in Maui, Hawaii. The attractants used were apple cider vinegar (ACV), brown rice vinegar (BRV), red wine (RW), apple cider vinegar and red wine (ACV+RW; 60/40), and brown rice vinegar and red wine (BRV+RW; 60/40). For D. suzukii, BRV+RW resulted in more captures than BRV, ACV, and RW, while ACV+RW resulted in more captures than ACV. No differences were observed between BRV+RW and ACV+RW. BRV had greater specificity in attracting D. suzukii compared to ACV, ACV+RW, and RW. For Z. indianus, no significant differences were observed in either the mean captures or specificity for any attractant used. Collectively, these findings demonstrate that (1) BRV and BRV+RW are effective field attractants and (2) D. suzukii has unique olfactory preferences compared to non-target drosophilids, while (3) Z. indianus’ preferences do not appear to vary from non-target drosophilids, and (4) the accuracy of relative abundance is impacted by the specificity of the attractants.

Associations Between Drosophila suzukii (Diptera: Drosophilidae) and Fungi in Raspberries

The invasive vinegar fly, Drosophila suzukii Matsumura, has emerged as one of the most serious arthropod pests of primocane red raspberries (Rubus ideaus L.) in the United States. In raspberries, D. suzukii encounter a diverse community of microbes, including fruit rot pathogens such as Botrytis cinerea Pers and Cladosporium cladosporioides de Vries. In this study, our primary objectives were to evaluate D. suzukii-fungal associations and determine D. suzukii's influence on fungal communities in raspberry fruit. Through culture-based surveys of larval gut microbes, we isolated several yeast fungi (primarily Hanseniaspora spp.), as well as Cladosporium, Botrytis, and several other non-yeast fungi from larval frass, suggesting that D. suzukii larvae encounter and feed on these fungi. Subsequent field surveys confirmed that D. suzukii larvae occurred in berries affected by Botrytis fruit rot and Cladosporium fruit rot. Under laboratory conditions, D. suzukii may facilitate C. cladosporioides infections, likely through the introduction of epiphytic propagules on the fruit surface. We could not detect impacts on B. cinerea infections or establish a clear vectoring relationship for either fruit rot. These studies provide evidence for an association between D. suzukii and fungal fruit rot pathogens. Understanding interactions between raspberry fruit, D. suzukii, and fungal microbes-especially whether D. suzukii facilitates the development of fruit rots or conversely, if fruit rots influence D. suzukii infestation patterns-may improve pest and pathogen management programs.

Draft Genome Sequence of the Candida zemplinina (syn., Starmerella bacillaris) Type Strain CBS 9494 [corrected]

Starmerella bacillaris is an ascomycetous yeast ubiquitously present in grapes and fermenting grape musts. In this report, we present the draft genome sequence of the S. bacillaris type strain CBS 9494, isolated from sweet botrytized wines, which will contribute to the study of this genetically heterogeneous wine yeast species.

Starmerella bacillaris is an ascomycetous yeast ubiquitously present in grapes and fermenting grape musts. In this report, we present the draft genome sequence of the S. bacillaris type strain CBS 9494, isolated from sweet botrytized wines, which will contribute to the study of this genetically heterogeneous wine yeast species.

Decomposition of biowaste macronutrients, microbes, and chemicals in black soldier fly larval treatment: A review

Processing of biowaste with larvae of the black soldier fly, Hermetia illucens L. (Diptera: Stratiomyidae), is an emerging waste treatment technology. Larvae grown on biowaste can be a relevant raw material for animal feed production and can therefore provide revenues for financially viable waste management systems. In addition, when produced on biowaste, insect-based feeds can be more sustainable than conventional feeds. Among others, the scalability of the technology will depend on the availability of large amounts of biowaste with a high process performance (e.g. bioconversion of organic matter to proteins and lipids) and microbial and chemical product safety. Currently, in contrast to other waste treatment technologies, such as composting or anaerobic digestion, the process performance is variable and the processes driving the decomposition of biowaste macronutrients, inactivation of microbes and fate of chemicals is poorly understood. This review presents the first summary of the most important processes involved in black soldier fly larvae (BSFL) treatment, based on the available knowledge concerning five well-studied fly species. This is a starting point to increase understanding regarding the processes of this technology, with the potential to increase its efficiency and uptake, and support the development of appropriate regulations. Based on this review, formulating different types of biowaste, e.g. to produce a diet with a similar protein content, a balanced amino acid profile and/or pre- and co-treatment of biowaste with beneficial microbes, has the potential to increase process performance. Following harvest, larvae require heat or other treatments for microbial inactivation and safety.

Persistence of Resident and Transplanted Genotypes of the Undomesticated Yeast Saccharomyces paradoxus in Forest Soil

Saccharomyces yeasts are intensively studied in biological research and in their domesticated roles in brewing and baking, and yet, remarkably little is known about their mode of life in forest soils. We report here that resident genotypes of the yeast S. paradoxus are persistent on a time scale of years in their microhabitats in forest soils. We also show that resident genotypes can be replaced by transplanted yeast genotypes. The high inoculum levels in experimental transplantations rapidly decreased over time, but the transplanted genotypes persisted at low abundance. We conclude that, in forest soils, Saccharomyces yeasts exist at very low abundance and that dispersal events are rare.

One might expect yeasts in soil to be highly dispersed via water or insects, forming ephemeral, genetically heterogeneous populations subject to competition and environmental stochasticity. Here, we report persistence of genotypes of the yeast Saccharomyces paradoxus in space and time. Within 1 km² in a mixed hardwood forest on scales from centimeters to tens of meters, we detected persistence over 3 years of native genotypes, identified by single nucleotide polymorphisms (SNPs) genome-wide, of the wild yeast Saccharomyces paradoxus growing around Quercus rubra and Quercus alba. Yeasts were recovered by enrichment in ethanol-containing medium, which measures only presence or absence, not abundance. Additional transplantation experiments employed strains marked with spontaneous defects in the URA3 gene, which also confer resistance to 5-fluoroorotic acid (5FOA). Plating soil suspensions from transplant sites on 5FOA-containing medium permitted one-step quantification of yeast CFU, with no interference from other unmarked yeasts or microorganisms. After an initial steep decrease in abundance, the yeast densities fluctuated over time, increasing in association with rainfall and decreasing in association with drought. After 18 months, the transplanted yeasts remained in place on the nine sites. In vitro transplantation experiments into nonsterile soil in petri dishes showed similar patterns of persistence and response to moisture and drought. To determine whether Saccharomyces cerevisiae, not previously recovered from soils regionally, can persist in our cold climate sites, we transplanted marked S. cerevisiae alone and in mixture with S. paradoxus in the fall of 2017. Five months later, S. cerevisiae persisted to the same extent as S. paradoxus.

IMPORTANCESaccharomyces yeasts are intensively studied in biological research and in their domesticated roles in brewing and baking, and yet, remarkably little is known about their mode of life in forest soils. We report here that resident genotypes of the yeast S. paradoxus are persistent on a time scale of years in their microhabitats in forest soils. We also show that resident genotypes can be replaced by transplanted yeast genotypes. The high inoculum levels in experimental transplantations rapidly decreased over time, but the transplanted genotypes persisted at low abundance. We conclude that, in forest soils, Saccharomyces yeasts exist at very low abundance and that dispersal events are rare.

Microbial Quantity Impacts Drosophila Nutrition, Development, and Lifespan

In Drosophila, microbial association can promote development or extend life. We tested the impact of microbial association during malnutrition and show that microbial quantity is a predictor of fly longevity. Although all tested microbes, when abundantly provided, can rescue lifespan on low-protein diet, the effect of a single inoculation seems linked to the ability of that microbial strain to thrive under experimental conditions. Microbes, dead or alive, phenocopy dietary protein, and the calculated dependence on microbial protein content is similar to the protein requirements determined from fly feeding studies, suggesting that microbes enhance host protein nutrition by serving as protein-rich food. Microbes that enhance larval growth are also associated with the ability to better thrive on fly culture medium. Our results suggest an unanticipated range of microbial species that promote fly development and longevity and highlight microbial quantity as an important determinant of effects on physiology and lifespan during undernutrition.

•

Microbial association promotes fly longevity and development on low-protein diet

•

A wide range of microbes can serve as a source of protein during undernutrition

•

The extent of effects correlates with microbiota quantity and biomass

•

The most impactful microbial species simply thrive on fly culture medium

The Drosophila model for microbiome research

The gut microbiome is increasingly recognized to play an important role in shaping the health and fitness of animals, including humans. Drosophila is emerging as a valuable model for microbiome research, combining genetic and genomic resources with simple protocols to manipulate the microbiome, such that microbiologically sterile flies and flies bearing a standardized microbiota can readily be produced in large numbers. Studying Drosophila has the potential to increase our understanding of how the microbiome influences host traits, and allows opportunities for hypothesis testing of microbial impacts on human health. Drosophila is being used to investigate aspects of host-microbe interactions, including the metabolism, the immune system and behavior. Drosophila offers a valuable alternative to rodent and other mammalian models of microbiome research for fundamental discovery of microbiome function, enabling improved research cost effectiveness and benefits for animal welfare.

The ecology of the Drosophila-yeast mutualism in wineries

The fruit fly, Drosophila melanogaster, is preferentially found on fermenting fruits. The yeasts that dominate the microbial communities of these substrates are the primary food source for developing D. melanogaster larvae, and adult flies manifest a strong olfactory system-mediated attraction for the volatile compounds produced by these yeasts during fermentation. Although most work on this interaction has focused on the standard laboratory yeast Saccharomyces cerevisiae, a wide variety of other yeasts naturally ferment fallen fruit. Here we address the open question of whether D. melanogaster preferentially associates with distinct yeasts in different, closely-related environments. We characterized the spatial and temporal dynamics of Drosophila-associated fungi in Northern California wineries that use organic grapes and natural fermentation using high-throughput, short-amplicon sequencing. We found that there is nonrandom structure in the fungal communities that are vectored by flies both between and within vineyards. Within wineries, the fungal communities associated with flies in cellars, fermentation tanks, and pomace piles are distinguished by varying abundances of a small number of yeast species. To investigate the origins of this structure, we assayed Drosophila attraction to, oviposition on, larval development in, and longevity when consuming the yeasts that distinguish vineyard microhabitats from each other. We found that wild fly lines did not respond differentially to the yeast species that distinguish winery habitats in habitat specific manner. Instead, this subset of yeast shares traits that make them attractive to and ensure their close association with Drosophila.

Phenotypic responses to microbial volatiles render a mold fungus more susceptible to insect damage

In decomposer systems, fungi show diverse phenotypic responses to volatile organic compounds of microbial origin (volatiles). The mechanisms underlying such responses and their consequences for the performance and ecological success of fungi in a multitrophic community context have rarely been tested explicitly. We used a laboratory‐based approach in which we investigated a tripartite yeast–mold–insect model decomposer system to understand the possible influence of yeast‐borne volatiles on the ability of a chemically defended mold fungus to resist insect damage. The volatile‐exposed mold phenotype (1) did not exhibit protein kinase A‐dependent morphological differentiation, (2) was more susceptible to insect foraging activity, and (3) had reduced insecticidal properties. Additionally, the volatile‐exposed phenotype was strongly impaired in secondary metabolite formation and unable to activate “chemical defense” genes upon insect damage. These results suggest that volatiles can be ecologically important factors that affect the chemical‐based combative abilities of fungi against insect antagonists and, consequently, the structure and dynamics of decomposer communities.

Yeast-insect associations: It takes guts

Insects interact with microorganisms in several situations, ranging from the accidental interaction to locate attractive food or the acquisition of essential nutrients missing in the main food source. Despite a wealth of studies recently focused on bacteria, the interactions between insects and yeasts have relevant implications for both of the parties involved. The insect intestine shows several structural and physiological differences among species, but it is generally a hostile environment for many microorganisms, selecting against the most sensitive and at the same time guaranteeing a less competitive environment to resistant ones. An intensive characterization of the interactions between yeasts and insects has highlighted their relevance not only for attraction to food but also for the insect's development and behaviour. Conversely, some yeasts have been shown to benefit from interactions with insects, in some cases by being carried among different environments. In addition, the insect intestine may provide a place to reside for prolonged periods and possibly mate or generate sexual forms able to mate once back in the external environments. YEA-May-17-0084.R3.

Physiological responses of insects to microbial fermentation products: Insights from the interactions between Drosophila and acetic acid

Acetic acid is a fermentation product of many microorganisms, including some that inhabit the food and guts of Drosophila. Here, we investigated the effect of dietary acetic acid on oviposition and larval performance of Drosophila. At all concentrations tested (0.34-3.4%), acetic acid promoted egg deposition by mated females in no-choice assays; and females preferred to oviposit on diet with acetic acid relative to acetic acid-free diet. However, acetic acid depressed larval performance, particularly extending the development time of both larvae colonized with the bacterium Acetobacter pomorum and axenic (microbe-free) larvae. The larvae may incur an energetic cost associated with dissipating the high acid load on acetic acid-supplemented diets. This effect was compounded by suppressed population growth of A. pomorum on the 3.4% acetic acid diet, such that the gnotobiotic Drosophila on this diet displayed traits characteristic of axenic Drosophila, specifically reduced developmental rate and elevated lipid content. It is concluded that acetic acid is deleterious to larval Drosophila, and hypothesized that acetic acid may function as a reliable cue for females to oviposit in substrates bearing microbial communities that promote larval nutrition.

Chemical Cues that Guide Female Reproduction in Drosophila melanogaster

Chemicals released into the environment by food, predators and conspecifics play critical roles in Drosophila reproduction. Females and males live in an environment full of smells, whose molecules communicate to them the availability of food, potential mates, competitors or predators. Volatile chemicals derived from fruit, yeast growing on the fruit, and flies already present on the fruit attract Drosophila, concentrating flies at food sites, where they will also mate. Species-specific cuticular hydrocarbons displayed on female Drosophila as they mature are sensed by males and act as pheromones to stimulate mating by conspecific males and inhibit heterospecific mating. The pheromonal profile of a female is also responsive to her nutritional environment, providing an honest signal of her fertility potential. After mating, cuticular and semen hydrocarbons transferred by the male change the female's chemical profile. These molecules make the female less attractive to other males, thus protecting her mate's sperm investment. Females have evolved the capacity to counteract this inhibition by ejecting the semen hydrocarbon (along with the rest of the remaining ejaculate) a few hours after mating. Although this ejection can temporarily restore the female's attractiveness, shortly thereafter another male pheromone, a seminal peptide, decreases the female's propensity to re-mate, thus continuing to protect the male's investment. Females use olfaction and taste sensing to select optimal egg-laying sites, integrating cues for the availability of food for her offspring, and the presence of other flies and of harmful species. We argue that taking into account evolutionary considerations such as sexual conflict, and the ecological conditions in which flies live, is helpful in understanding the role of highly species-specific pheromones and blends thereof, as well as an individual's response to the chemical cues in its environment.

Chemical signaling and insect attraction is a conserved trait in yeasts

Yeast volatiles attract insects, which apparently is of mutual benefit, for both yeasts and insects. However, it is unknown whether biosynthesis of metabolites that attract insects is a basic and general trait, or if it is specific for yeasts that live in close association with insects. Our goal was to study chemical insect attractants produced by yeasts that span more than 250 million years of evolutionary history and vastly differ in their metabolism and lifestyle. We bioassayed attraction of the vinegar fly Drosophila melanogaster to odors of phylogenetically and ecologically distinct yeasts grown under controlled conditions. Baker's yeast Saccharomyces cerevisiae, the insect-associated species Candida californica, Pichia kluyveri and Metschnikowia andauensis, wine yeast Dekkera bruxellensis, milk yeast Kluyveromyces lactis, the vertebrate pathogens Candida albicans and Candida glabrata, and oleophilic Yarrowia lipolytica were screened for fly attraction in a wind tunnel. Yeast headspace was chemically analyzed, and co-occurrence of insect attractants in yeasts and flowering plants was investigated through a database search. In yeasts with known genomes, we investigated the occurrence of genes involved in the synthesis of key aroma compounds. Flies were attracted to all nine yeasts studied. The behavioral response to baker's yeast was independent of its growth stage. In addition to Drosophila, we tested the basal hexapod Folsomia candida (Collembola) in a Y-tube assay to the most ancient yeast, Y. lipolytica, which proved that early yeast signals also function on clades older than neopteran insects. Behavioral and chemical data and a search for selected genes of volatile metabolites underline that biosynthesis of chemical signals is found throughout the yeast clade and has been conserved during the evolution of yeast lifestyles. Literature and database reviews corroborate that yeast signals mediate mutualistic interactions between insects and yeasts. Moreover, volatiles emitted by yeasts are commonly found also in flowers and attract many insect species. The collective evidence suggests that the release of volatile signals by yeasts is a widespread and phylogenetically ancient trait, and that insect-yeast communication evolved prior to the emergence of flowering plants. Co-occurrence of the same attractant signals in yeast and flowers suggests that yeast-insect communication may have contributed to the evolution of insect-mediated pollination in flowers.

Microbial community assembly in wild populations of the fruit fly Drosophila melanogaster

Animals are routinely colonized by microorganisms. Despite many studies documenting the microbial taxa associated with animals, the pattern and ecological determinants of among-animal variation in microbial communities are poorly understood. This study quantified the bacterial communities associated with natural populations of Drosophila melanogaster. Across five collections, each fly bore 16-78 OTUs, predominantly of the Acetobacteraceae, Lactobacillaceae, and Enterobacteriaceae. Positive relationships, mostly among related OTUs, dominated both the significant co-occurrences and co-association networks among bacteria, and OTUs with important network positions were generally of intermediate abundance and prevalence. The prevalence of most OTUs was well predicted by a neutral model suggesting that ecological drift and passive dispersal contribute significantly to microbiome composition. However, some Acetobacteraceae and Lactobacillaceae were present in more flies than predicted, indicative of superior among-fly dispersal. These taxa may be well-adapted to the Drosophila habitat from the perspective of dispersal as the principal benefit of the association to the microbial partners. Taken together, these patterns indicate that both stochastic processes and deterministic processes relating to the differential capacity for persistence in the host habitat and transmission between hosts contribute to bacterial community assembly in Drosophila melanogaster.