Symbiosis: Gut Bacteria Manipulate Host Behaviour

Diet Influences the Gut Microbial Diversity and Olfactory Preference of the German Cockroach Blattella germanica

The gut microbiota of insects has been proven to play a role in the host's nutrition and foraging. The German cockroach, Blattella germanica, is an important vector of various pathogens and causes severe allergic reactions in humans. Food bait is an effective and frequently used method of controlling this omnivorous insect. Thus, understanding the relationships among diet, gut microbiota, and olfactory preferences could be useful for optimizing this management strategy. In this study, B. germanica was exposed to different foods, i.e., high-fat diet, high-protein diet, high-starch diet, and dog food (as control). Then their gut microbial and olfactory responses were investigated. 16S rRNA gene sequencing confirmed that the gut microbiota significantly differed across the four treatments, especially in relation to bacteria associated with the metabolism and digestion of essential components. Behavioral tests and the antenna electrophysiological responses showed that insects had a greater preference for other types of diets compared with their long-term domesticated diet. Moreover, continuously providing a single-type diet could change almost all the OR genes' expression of B. germanica, especially BgORco, which was significantly repressed compared to control. These results indicate that diet can shape the gut microbiota diversity and drive the olfactory preference of B. germanica. The association between gut microbiota profiles and diets can be utilized in managing B. germanica according to their olfactory preference.

Impact of disinfectants on the intestinal bacterial symbionts and immunity of silkworm (Bombyx mori L.)

The insect egg surface can serve as a vehicle for vertical symbiont transmission from the maternal parent to its offspring. Hypochlorite and formaldehyde are two common disinfectants used for insect egg surface sterilization. Here, we explored the intestinal microecology and immune response profile of the silkworm Bombyx mori strain Dazao after disinfectant exposure by using high-throughput sequencing technology and real-time PCR analysis. After egg surface sterilization, no significant difference (P > 0.05) in overall body weight was observed among the control, sodium hypochlorite, and formaldehyde groups. 16S rRNA metagenomic sequencing revealed that the main abundant intestinal bacteria were Enterococcus, Burkholderia, Phenylobacterium, Ralstonia, Chitinophaga, Bradyrhizobium, Herbaspirillum, and two unclassified Bacteroidetes species. Egg surface sterilization evidently altered the composition and abundance of intestinal microbiota but did not significantly change its alpha diversity. The dysbiosis of intestinal microbiota resulted in the perturbation of the immune response profile of the silkworm intestine. Our findings reveal that hypochlorite has a blocking effect on the symbiont transmission compared with formaldehyde. More importantly, egg surface sterilization exerts substantial effects on the ecophysiological traits of insects. The present study contributes to the scientific and reasonable application of disinfectants for insect egg surface sterilization during industrial silk production and laboratory-scale insect rearing.

Effect of a Probiotic-Enriched Diet on Sexual Competitiveness, Pheromone Emission, and Cuticular Hydrocarbons of Sterile and Fertile Anastrepha ludens (Diptera: Tephritidae)

The sterile insect technique has been used for the eradication or control of numerous tephritid fruit flies. However, mass-rearing and sterilization can affect the microbiota and sexual performance of male tephritid fruit flies. Despite the addition of postteneral protein food which contributes to the enhancement of the sexual performance of mass-reared males, in some cases, they are less competitive than their wild counterparts. Alternatively, the addition of probiotics may improve the sexual performance of mass-reared sterile males. In this study, we evaluated the effect of a postteneral Lactobacillus casei-enriched diet on the sexual competitivity, pheromone emission, and cuticular hydrocarbons of mass-reared sterile and fertile Anastrepha ludens (Loew) (Diptera: Tephritidae) males. Flies were fed either with sugar, standard diet (sugar and protein, 3:1), sugar + probiotic, or standard diet + probiotic. The addition of the probiotic improved the sexual competitivity of fertile and sterile males that were devoid of protein but led to a negative effect on males fed with a standard diet. As compared to males that were fed with the standard diet + probiotic/only sugar, the males fed with the standard diet or those fed on sugar + probiotic displayed a higher number of mating instances. Sterile males that fed on sugar + probiotic had a higher relative amount of anastrephine, epianastrephine, n-methyl octacosane, and 2-methyl triacontane than those fed on sugar only. Overall, these compounds were common in the treatments where males had the best sexual performance. Our results suggest that the probiotics offer nutritional advantages to males whose food lacks protein.

Gut symbiotic bacteria are involved in nitrogen recycling in the tephritid fruit fly Bactrocera dorsalis

Background

Nitrogen is considered the most limiting nutrient element for herbivorous insects. To alleviate nitrogen limitation, insects have evolved various symbiotically mediated strategies that enable them to colonize nitrogen-poor habitats or exploit nitrogen-poor diets. In frugivorous tephritid larvae developing in fruit pulp under nitrogen stress, it remains largely unknown how nitrogen is obtained and larval development is completed.

Results

In this study, we used metagenomics and metatranscriptomics sequencing technologies as well as in vitro verification tests to uncover the mechanism underlying the nitrogen exploitation in the larvae of Bactrocera dorsalis. Our results showed that nitrogenous waste recycling (NWR) could be successfully driven by symbiotic bacteria, including Enterobacterales, Lactobacillales, Orbales, Pseudomonadales, Flavobacteriales, and Bacteroidales. In this process, urea hydrolysis in the larval gut was mainly mediated by Morganella morganii and Klebsiella oxytoca. In addition, core bacteria mediated essential amino acid (arginine excluded) biosynthesis by ammonium assimilation and transamination.

Conclusions

Symbiotic bacteria contribute to nitrogen transformation in the larvae of B. dorsalis in fruit pulp. Our findings suggest that the pattern of NWR is more likely to be applied by B. dorsalis, and M. morganii, K. oxytoca, and other urease-positive strains play vital roles in hydrolysing nitrogenous waste and providing metabolizable nitrogen for B. dorsalis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12915-022-01399-9.

Divergence together with microbes: A comparative study of the associated microbiomes in the closely related Littorina species

Any multicellular organism during its life is involved in relatively stable interactions with microorganisms. The organism and its microbiome make up a holobiont, possessing a unique set of characteristics and evolving as a whole system. This study aimed to evaluate the degree of the conservativeness of microbiomes associated with intertidal gastropods. We studied the composition and the geographic and phylogenetic variability of the gut and body surface microbiomes of five closely related sympatric Littorina (Neritrema) spp. and a more distant species, L. littorea, from the sister subgenus Littorina (Littorina). Although snail-associated microbiomes included many lineages (207–603), they were dominated by a small number of OTUs of the genera Psychromonas, Vibrio, and Psychrilyobacter. The geographic variability was greater than the interspecific differences at the same collection site. While the microbiomes of the six Littorina spp. did not differ at the high taxonomic level, the OTU composition differed between groups of cryptic species and subgenera. A few species-specific OTUs were detected within the collection sites; notably, such OTUs never dominated microbiomes. We conclude that the composition of the high-rank taxa of the associated microbiome (“scaffolding enterotype”) is more evolutionarily conserved than the composition of the low-rank individual OTUs, which may be site- and / or species-specific.

Bacterial symbiosis in Bactrocera oleae, an Achilles' heel for its pest control

Investigations on microbial symbioses in Tephritidae have increased over the past 30 years owing to the potential use of these relationships in developing new control strategies for economically important fruit flies. Bactrocera oleae (Rossi)-the olive fruit fly-is a monophagous species strictly associated with the olive tree, and among all the tephritids, its symbionts are the most investigated. The bacterium Candidatus Erwinia dacicola is the major persistent resident endosymbiont in wild B. oleae populations. Its relationship with B. oleae has been investigated since being identified in 2005. This endosymbiont is vertically transmitted through generations from the female to the egg. It exists at every developmental stage, although it is more abundant in larvae and ovipositing females, and is necessary for both larvae and adults. Studying B. oleae-Ca. E. dacicola, or other B. oleae-microbe interactions, will allow us to develop modern biological control systems for area-wide olive protection and set an example for similar programs in other important food crops. This review summarizes the information available on tephritid-microbe interactions and investigates relationships among fruit flies, bacteria and host plants; however, its focus is on B. oleae and its strict association with Ca. E. dacicola to promote environmentally friendly control strategies for area-wide pest management.

Systemic Regulation of Host Energy and Oogenesis by Microbiome-Derived Mitochondrial Coenzymes

Gut microbiota have been shown to promote oogenesis and fecundity, but the mechanistic basis of remote influence on oogenesis remained unknown. Here, we report a systemic mechanism of influence mediated by bacterial-derived supply of mitochondrial coenzymes. Removal of microbiota decreased mitochondrial activity and ATP levels in the whole-body and ovary, resulting in repressed oogenesis. Similar repression was caused by RNA-based knockdown of mitochondrial function in ovarian follicle cells. Reduced mitochondrial function in germ-free (GF) females was reversed by bacterial recolonization or supplementation of riboflavin, a precursor of FAD and FMN. Metabolomics analysis of GF females revealed a decrease in oxidative phosphorylation and FAD levels and an increase in metabolites that are degraded by FAD-dependent enzymes (e.g., amino and fatty acids). Riboflavin supplementation opposed this effect, elevating mitochondrial function, ATP, and oogenesis. These findings uncover a bacterial-mitochondrial axis of influence, linking gut bacteria with systemic regulation of host energy and reproduction.

Attractiveness and Sexual Competitiveness of Anastrepha obliqua Males (Diptera: Tephritidae) Fed on a Diet Enriched With Providencia rettgeri

The West Indian fruit fly, Anastrepha obliqua (Macquart), is the second most important tephritid fruit fly in Mexico, infesting mango, hog plum and guava fruits. To control this pest, the Mexican government has implemented the use of the sterile insect technique (SIT), which involves the mass production, sterilization and release of flies. However, the A. obliqua laboratory males used in SIT are selected to a lesser extent by the wild females during competitiveness tests. The objective of this study was to compare the effects of males fed on fruit fly food enriched with Providencia rettgeri to those in males fed on food alone, assessing male mating competitiveness, capture of females using traps baited with males fed with the enriched diet and sex pheromone components. The results indicated that males fed with the diet enriched with P. rettgeri had increased mating competitiveness and captured more females in the field cage tests. However, no difference was observed in the proportion of volatile sex pheromone components identified during the calling of A. obliqua males. The results suggest the value of incorporating bacteria into the mass rearing technique of A. obliqua adults in order to improve the sexual competitiveness of males from the laboratory compared to wild males.

Locust Bacterial Symbionts: An Update

As one of the world's most infamous agricultural pests, locusts have been subjected to many in-depth studies. Their ability at one end of their behavioral spectrum to live as solitary individuals under specific conditions, and at the other end of the spectrum to form swarms of biblical scale, has placed them at the focus of vast research efforts. One important aspect of locust ecology is that of their interactions with the bacteria that reside in and on them. Although this aspect of locust ecology has been little studied relative to the mainstream locust research, these bacteria have been shown both to affect locust immunity and to participate in maintaining swarm integrity through the secretion of attractant volatiles. The interaction between locusts and their bacteria seems, however, to be bi-directional, with the bacteria themselves, as recently shown, being influenced by their host's swarming tendencies. This seems to be a consequence of the bacterial composition in the locust's gut, reproductive organs, and integument undergoing change with the change in their host's behavior. In this review we describe the current state of knowledge of the locust-bacteria interactions (data exists mainly for the desert and the migratory locusts), as well as highlighting some newly-gained understanding; and offer perspectives for future research.

Transmission efficiency drives host-microbe associations

Sequencing technologies have fuelled a rapid rise in descriptions of microbial communities associated with hosts, but what is often harder to ascertain is the evolutionary significance of these symbioses. Here, we review the role of vertical (VT), horizontal (HT), environmental acquisition and mixed modes of transmission (MMT), in the establishment of animal host–microbe associations. We then model four properties of gut microbiota proposed as key to promoting animal host–microbe relationships: modes of transmission, host reproductive mode, host mate choice and host fitness. We found that: (i) MMT led to the highest frequencies of host–microbe associations, and that some environmental acquisition or HT of microbes was required for persistent associations to form unless VT was perfect; (ii) host reproductive mode (sexual versus asexual) and host mate choice (for microbe carriers versus non-carriers) had little impact on the establishment of host–microbe associations; (iii) host mate choice did not itself lead to reproductive isolation, but could reinforce it; and (iv) changes in host fitness due to host–microbe associations had a minimal impact upon the formation of co-associations. When we introduced a second population, into which host–microbe carriers could disperse but in which environmental acquisition did not occur, highly efficient VT was required for host–microbe co-associations to persist. Our study reveals that transmission mode is of key importance in establishing host–microbe associations.

Dynamics of Insect-Microbiome Interaction Influence Host and Microbial Symbiont

Insects share an intimate relationship with their gut microflora and this symbiotic association has developed into an essential evolutionary outcome intended for their survival through extreme environmental conditions. While it has been clearly established that insects, with very few exceptions, associate with several microbes during their life cycle, information regarding several aspects of these associations is yet to be fully unraveled. Acquisition of bacteria by insects marks the onset of microbial symbiosis, which is followed by the adaptation of these bacterial species to the gut environment for prolonged sustenance and successful transmission across generations. Although several insect-microbiome associations have been reported and each with their distinctive features, diversifications and specializations, it is still unclear as to what led to these diversifications. Recent studies have indicated the involvement of various evolutionary processes operating within an insect body that govern the transition of a free-living microbe to an obligate or facultative symbiont and eventually leading to the establishment and diversification of these symbiotic relationships. Data from various studies, summarized in this review, indicate that the symbiotic partners, i.e., the bacteria and the insect undergo several genetic, biochemical and physiological changes that have profound influence on their life cycle and biology. An interesting outcome of the insect-microbe interaction is the compliance of the microbial partner to its eventual genome reduction. Endosymbionts possess a smaller genome as compared to their free-living forms, and thus raising the question what is leading to reductive evolution in the microbial partner. This review attempts to highlight the fate of microbes within an insect body and its implications for both the bacteria and its insect host. While discussion on each specific association would be too voluminous and outside the scope of this review, we present an overview of some recent studies that contribute to a better understanding of the evolutionary trajectory and dynamics of the insect-microbe association and speculate that, in the future, a better understanding of the nature of this interaction could pave the path to a sustainable and environmentally safe way for controlling economically important pests of crop plants.

The Lovebug Effect: Is the human biophilic drive influenced by interactions between the host, the environment, and the microbiome?

Psychological frameworks are often used to investigate the mechanisms involved with our affinity towards, and connection with nature--such as the Biophilia Hypothesis and Nature Connectedness. Recent revelations from microbiome science suggest that animal behaviour can be strongly influenced by the host's microbiome--for example, via the bidirectional communication properties of the gut-brain axis. Here, we build on this theory to hypothesise that a microbially-influenced mechanism could also contribute to the human biophilic drive - the tendency for humans to affiliate and connect with nature. Humans may be at an evolutionary advantage through health-regulating exchange of environmental microbiota, which in turn could influence our nature affinity. We present a conceptual model for microbially-influenced nature affinity, calling it the Lovebug Effect. We present an overview of the potential mechanistic pathways involved in the Lovebug Effect, and consider its dependence on the hologenome concept of evolution, direct behavioural manipulation, and host-microbiota associated phenotypes independent of these concepts. We also discuss its implications for human health and ecological resilience. Finally, we highlight several possible approaches to scrutinise the hypothesis. The Lovebug Effect could have important implications for our understanding of exposure to natural environments for health and wellbeing, and could contribute to an ecologically resilient future.

"Us vs. Them" Pair Housing: Effects on Body Weight, Open Field Behavior, and Gut Microbiota in Rats Selectively Bred on a Taste Phenotype

Taste is increasingly recognized as being related to reward, risk, and social processes beyond the ingestive domain. Occidental High (HiS) and Low (LoS) Saccharin Consuming rats have been selectively bred for more than 25 years to study those relationships. The present study examined LoS and HiS rats' sensitivity to a social partner's lineage. The role of gut microbiome transfer between lines was also explored as a possible mediating mechanism. Rats were pair-housed with a rat from either their own line (same-line condition) or the other line (other-line condition); weight gain, saccharin intake, acoustic startle, and open field behavior were measured. Results show for the first time that the lines express different behavioral strategies in a novel open field. In addition, weight gain and open field measures indicate that other-line housing was stressful. Saccharin intake, however, was unaffected by housing condition. A previous finding that the lines possess different gut microbiota was replicated. Although microbial transfer occurred between social partners, no clear evidence was obtained that housing-condition effects on weight gain or behavior were mediated by microbial transfer. Overall, these findings add to the characterization of non-gustatory correlates of a taste phenotype and suggest that rats differing strikingly on the taste phenotype and/or its correlates may be socially incompatible.

Adjusting the Prerelease Gut Microbial Community by Diet Training to Improve the Postrelease Fitness of Captive-Bred Acipenser dabryanus

As one of the most important tool for biodiversity restoration and endangered species conservation, reintroduction has been implemented worldwide. In reintroduction projects, prerelease conditioning could effectively increase postrelease fitness and survival by improving animals’ adaptation to transformation from artificial to natural environments. However, how early-life diet training affects individuals’ adaptation, fitness, and survival after release remains largely unknown. We hypothesized that early-life diet training would adjust the host’s gut microbial community, the gut microbial community would influence the host’s diet preference, and the host’s diet preference would impact its adaptation to diet provision transformation and then determine postrelease fitness and survival. To verify this hypothesis, we investigated the growth characteristics and gut microbes of Yangtze sturgeon (Acipenser dabryanus) trained with natural and formula diets at both the prerelease and postrelease stages. The results showed that (1) the gut microbial communities of the individuals trained with a natural diet (i.e., natural diet group) and formula diet (i.e., formula diet group) evolved to the optimal status for their corresponding diet provisions, (2) the individuals in the natural diet group paid a lower cost (i.e., changed their gut microbial communities less) during diet transformation and release into the natural environment than did the individuals in the formula diet group, and (3) the gut microbes in the natural diet group better supported postrelease fitness and survival than did the gut microbes in the formula diet group. The results indicated that better prerelease diet training with more appropriate training diets and times could improve the reintroduction of Yangtze sturgeon by adjusting the prerelease gut microbial community. Because a relationship between diet (preference) and gut microbes is common in animals from insects (such as Drosophila melanogaster) to mammals (such as Homo sapiens), our hypothesis verified by the case study on Yangtze sturgeon applies to other animals. We therefore encourage future studies to identify optimal training diets and times for each species to best adjust its prerelease gut microbial community and then improve its postrelease fitness and survival in reintroduction projects.

Effect of host fruit, temperature and Wolbachia infection on survival and development of Ceratitis capitata immature stages

The Mediterranean fruit fly, Ceratitis capitata (Diptera: Tephritidae), holds an impressive record of successful invasions promoted by the growth and development of international fruit trade. Hence, survival of immatures within infested fruit that are subjected to various conditions during transportation seems to be a crucial feature that promotes invasion success. Wolbachia pipientis is a common endosymbiont of insects and other arthropods generating several biological effects on its hosts. Existing information report the influence of Wolbachia on the fitness traits of insect host species, including the Mediterranean fruit fly. However, little is known regarding effects of Wolbachia infection on immature development in different host fruits and temperatures. This study was conducted to determine the development and survival of immature stages of four different Mediterranean fruit fly populations, either infected or uninfected with Wolbachia, in two hosts (apples, bitter oranges) under three constant temperatures (15, 25 and 30°C), constant relative humidity (45-55 ± 5%), and a photoperiod of 14L:10D. Our findings demonstrate both differential response of two fruit fly lines to Wolbachia infection and differential effects of the two Wolbachia strains on the same Mediterranean fruit fly line. Larva-to-pupa and larva-to-adult survival followed similar patterns and varied a lot among the four medfly populations, the two host fruits and the different temperatures. Pupation rates and larval developmental time were higher for larvae implanted in apples compared to bitter oranges. The survival rates of wildish medflies were higher than those of the laboratory adapted ones, particularly in bitter oranges. The Wolbachia infected medflies, expressed lower survival rates and higher developmental times, especially the wCer4 infected line. High temperatures constrained immature development and were lethal for the Wolbachia infected wCer4 medfly line. Lower temperatures inferred longer developmental times to immature stages of all medfly populations tested, in both host fruits. Implications on the ecology and survival of the fly in nature are discussed.

Disrupting butterfly caterpillar microbiomes does not impact their survival and development

Associations with gut microbes are believed to play crucial roles in the physiology, immune function, development and behaviour of insects. However, microbiome sequencing has recently suggested that butterflies are an anomaly, because their microbiomes do not show strong host- and developmental stage-specific associations. We experimentally manipulated butterfly larval gut microbiota and found that disrupting gut microbes had little influence on larval survival and development. Larvae of the butterflies Danaus chrysippus and Ariadne merione that fed on chemically sterilized or antibiotic-treated host plant leaves had significantly reduced bacterial loads, and their gut bacterial communities were disrupted substantially. However, neither host species treated this way suffered a significant fitness cost: across multiple experimental blocks, treated and control larvae had similar survival, growth and development. Furthermore, re-introducing microbes from the excreta of control larvae did not improve larval growth and survival. Thus, these butterfly larvae did not appear to rely on specialized gut bacteria for digestion, detoxification, biomass accumulation and metamorphosis. Our experiments thus show that dependence on gut bacteria for growth and survival is not a universal phenomenon across insects. Our findings also caution that strategies which target gut microbiomes may not always succeed in controlling Lepidopteran pests.

Bacterial communities in digestive and excretory organs of cicadas

Bacteriocyte-associated symbionts are essential for the health of many sap-sucking insects, such as cicadas, leafhoppers and treehoppers, etc., but little is known about the bacterial community in the gut and other related organs in these insects. We characterized the bacterial communities in the salivary glands, alimentary canal and the Malpighian tubules of two populations of the cicada Subpsaltria yangi occurring in different habitats and feeding on different hosts. A high degree of similarity of core microbiota was revealed between the two populations, both with the top three bacteria belonging to Meiothermus, Candidatus Sulcia and Halomonas. The bacterial communities in various organs clustered moderately by populations possibly reflect adaptive changes in the microbiota of related S. yangi populations, which provide a better understanding of the speciation and adaptive mechanism of this species to different diets and habitats. When compared with two phylogenetically distant cicada species, Hyalessa maculaticollis and Meimuna mongolica, the core microbiota in S. yangi was significantly different to that of these species. In addition, our results confirm that Ca. Sulcia distributes in the digestive and excretory organs besides the bacteriomes and gonads, which provide potential important information onto the trophic functions of this obligate endosymbiont to the host insects.

Symbiotic bacteria motivate the foraging decision and promote fecundity and survival of Bactrocera dorsalis (Diptera: Tephritidae)

Background

The gut bacteria of tephritid fruit flies play prominent roles in nutrition, reproduction, maintenance and ecological adaptations of the host. Here, we adopted an approach based on direct observation of symbiotic or axenic flies feeding on dishes seeded with drops of full diet (containing all amino acids) or full diet supplemented with bacteria at similar concentrations to explore the effects of intestinal bacteria on foraging decision and fitness of Bactrocera dorsalis.

Results

The results show that intestinal probiotics elicit beneficial foraging decision and enhance the female reproduction fitness and survival of B. dorsalis (symbiotic and axenic), yet preferences for probiotic diets were significantly higher in axenic flies to which they responded faster compared to full diet. Moreover, females fed diet supplemented with Pantoea dispersa and Enterobacter cloacae laid more eggs but had shorter lifespan while female fed Enterococcus faecalis and Klebsiella oxytoca enriched diets lived longer but had lower fecundity compared to the positive control. Conversely, flies fed sugar diet (negative control) were not able to produce eggs, but lived longer than those from the positive control.

Conclusions

These results suggest that intestinal bacteria can drive the foraging decision in a way which promotes the reproduction and survival of B. dorsalis. Our data highlight the potentials of gut bacterial isolates to control the foraging behavior of the fly and empower the sterile insect technique (SIT) program through the mass rearing.

Why does the microbiome affect behaviour?

Growing evidence indicates that the mammalian microbiome can affect behaviour, and several symbionts even produce neurotransmitters. One common explanation for these observations is that symbionts have evolved to manipulate host behaviour for their benefit. Here, we evaluate the manipulation hypothesis by applying evolutionary theory to recent work on the gut-brain axis. Although the theory predicts manipulation by symbionts under certain conditions, these appear rarely satisfied by the genetically diverse communities of the mammalian microbiome. Specifically, any symbiont investing its resources to manipulate host behaviour is expected to be outcompeted within the microbiome by strains that do not manipulate and redirect their resources into growth and survival. Moreover, current data provide no clear evidence for manipulation. Instead, we show how behavioural effects can readily arise as a by-product of natural selection on microorganisms to grow within the host and natural selection on hosts to depend upon their symbionts. We argue that understanding why the microbiome influences behaviour requires a focus on microbial ecology and local effects within the host.

Symbiotic bacteria affect oviposition behavior in the olive fruit fly Bactrocera oleae

Microbial associations are widespread across the insects. In the olive fruit fly Bactrocera oleae (Diptera: Tephritidae), vertically transmitted gut symbionts contribute to larval development inside the olive host, and to adult nutrition. Nevertheless, their effect on behavioural decisions of adults is unknown. In this study, we show that symbiotic bacteria affect oviposition behaviour in B. oleae. We studied the effect of different fruits as hosts and different gut-bacteria as gut-symbionts on oviposition attempts and fly development in B. oleae. Untreated flies that had native gut-symbionts attempted oviposition significantly more times than axenic flies as well as flies treated with medfly-associated Pantoea or Klebsiella bacteria. Axenic flies provided with a diet containing the homogenized gut of symbiotic flies recovered the same number of oviposition attempts as their symbiotic counterparts. As for as the different hosts, green olives (unripe) and grapes were preferred while black olives (ripe) elicited the least number of oviposition attempts, with an interactive effect of host and bacterial treatments. It appears that both the host attributes and the native gut-symbionts drive oviposition preference towards green olives in B. oleae. Moreover, both bacterial treatments and hosts significantly affected the development of B. oleae larvae. Though grapes elicited as many oviposition attempts as green olives, they yielded no pupae. Taken together, our results suggest that the intimate association between B. oleae and their gut-microbes, extends beyond nutritional support to behaviour.

Intestinal bacteria modulate the foraging behavior of the oriental fruit fly Bactrocera dorsalis (Diptera: Tephritidae)

The gut microbiome of insects directly or indirectly affects the metabolism, immune status, sensory perception and feeding behavior of its host. Here, we examine the hypothesis that in the oriental fruit fly (Bactrocera dorsalis, Diptera: Tephritidae), the presence or absence of gut symbionts affects foraging behavior and nutrient ingestion. We offered protein-starved flies, symbiotic or aposymbiotic, a choice between diets containing all amino acids or only the non-essential ones. The different diets were presented in a foraging arena as drops that varied in their size and density, creating an imbalanced foraging environment. Suppressing the microbiome resulted in significant changes of the foraging behavior of both male and female flies. Aposymbiotic flies responded faster to the diets offered in experimental arenas, spent more time feeding, ingested more drops of food, and were constrained to feed on time-consuming patches (containing small drops of food), when these offered the full complement of amino acids. We discuss these results in the context of previous studies on the effect of the gut microbiome on host behavior, and suggest that these be extended to the life history dimension.

Interactions between the sexual identity of the nervous system and the social environment mediate lifespan in Drosophila melanogaster

Sex differences in lifespan are ubiquitous, but the underlying causal factors remain poorly understood. Inter- and intrasexual social interactions are well known to influence lifespan in many taxa, but it has proved challenging to separate the role of sex-specific behaviours from wider physiological differences between the sexes. To address this problem, we genetically manipulated the sexual identity of the nervous system-and hence sexual behaviour-in Drosophila melanogaster, and measured lifespan under varying social conditions. Consistent with previous studies, masculinization of the nervous system in females induced male-specific courtship behaviour and aggression, while nervous system feminization in males induced male-male courtship and reduced aggression. Control females outlived males, but masculinized female groups displayed male-like lifespans and male-like costs of group living. By varying the mixture of control and masculinized females within social groups, we show that male-specific behaviours are costly to recipients, even when received from females. However, consistent with recent findings, our data suggest courtship expression to be surprisingly low cost. Overall, our study indicates that nervous system-mediated expression of sex-specific behaviour per se-independent of wider physiological differences between the sexes, or the receipt of aggression or courtship-plays a limited role in mediating sex differences in lifespan.