The gene "degrees of kevin bacon" (dokb) regulates a social network behaviour in Drosophila melanogaster.

Social networks are a mathematical representation of interactions among individuals which are prevalent across various animal species. Studies of human populations have shown the breadth of what can spread throughout a social network: obesity, smoking cessation, happiness, drug use and divorce. 'Betweenness centrality' is a key property of social networks that indicates an individual's importance in facilitating communication and cohesion within the network. Heritability of betweenness centrality has been suggested in several species, however the genetic regulation of this property remains enigmatic. Here, we demonstrate that the gene CG14109, referred to as degrees of kevin bacon (dokb), influences betweenness centrality in Drosophila melanogaster. We identify strain-specific alleles of dokb with distinct amino acid sequences and when the dokb allele is exchanged between strains, flies exhibit the betweenness centrality pattern dictated by the donor allele. By inserting a GAL4 reporter into the dokb locus, we confirm that dokb is expressed in the central nervous system. These findings define a novel genetic entry point to study social network structure and thereby establish gene-to-social structure relationships. While dokb sequence homology is exclusive to Diptera, we anticipate that dokb-associated molecular pathways could unveil convergent neural mechanisms of social behaviour that apply in diverse animal species.

UBR4/POE facilitates secretory trafficking to maintain circadian clock synchrony.

Ubiquitin ligases control the degradation of core clock proteins to govern the speed and resetting properties of the circadian pacemaker. However, few studies have addressed their potential to regulate other cellular events within clock neurons beyond clock protein turnover. Here, we report that the ubiquitin ligase, UBR4/POE, strengthens the central pacemaker by facilitating neuropeptide trafficking in clock neurons and promoting network synchrony. Ubr4-deficient mice are resistant to jetlag, whereas poe knockdown flies are prone to arrhythmicity, behaviors reflective of the reduced axonal trafficking of circadian neuropeptides. At the cellular level, Ubr4 ablation impairs the export of secreted proteins from the Golgi apparatus by reducing the expression of Coronin 7, which is required for budding of Golgi-derived transport vesicles. In summary, UBR4/POE fulfills a conserved and unexpected role in the vesicular trafficking of neuropeptides, a function that has important implications for circadian clock synchrony and circuit-level signal processing.

The gut microbiome defines social group membership in honey bee colonies.

In the honey bee, genetically related colony members innately develop colony-specific cuticular hydrocarbon profiles, which serve as pheromonal nestmate recognition cues. Yet, despite high intracolony relatedness, the innate development of colony-specific chemical signatures by individual colony members is largely determined by the colony environment, rather than solely relying on genetic variants shared by nestmates. Therefore, it is puzzling how a nongenic factor could drive the innate development of a quantitative trait that is shared by members of the same colony. Here, we provide one solution to this conundrum by showing that nestmate recognition cues in honey bees are defined, at least in part, by shared characteristics of the gut microbiome across individual colony members. These results illustrate the importance of host-microbiome interactions as a source of variation in animal behavioral traits.

Desiccation resistance is an adaptive life-history trait dependent upon cuticular hydrocarbons, and influenced by mating status and temperature in D. melanogaster.

Terrestrial insects are susceptible to desiccation and conserve internal water stores by preventing the loss of water due to transpiration across the cuticle. The epicuticle, a thin waxy layer on the outer surface of the insect cuticle is comprised primarily of a complex blend of cuticular hydrocarbons (CHCs) and is integral to preventing cuticular water loss. How the composition of epicuticular lipids (quantity and quality of the specific hydrocarbons) relates to desiccation resistance, however, has been difficult to determine. Here, we establish a model system to test the capacity of CHCs to protect against desiccation in the vinegar fly, Drosophila melanogaster. Using this system, we demonstrate that the oenocytes and CHCs produced by these cells are critically important for desiccation resistance, as measured by survival under desiccative conditions. Additionally, we show that both mating status and developmental temperature influence desiccation resistance. Prior mating increased desiccation survival through the direct transfer of CHCs between sexual partners, as well as through a female-specific response to a male-derived factor transferred during copulation. Together, our results demonstrate that desiccation resistance is an adaptive life-history trait dependent upon CHCs and influenced by prior social interactions and environmental conditions.

The cuticular hydrocarbon profiles of honey bee workers develop via a socially-modulated innate process.

Large social insect colonies exhibit a remarkable ability for recognizing group members via colony-specific cuticular pheromonal signatures. Previous work suggested that in some ant species, colony-specific pheromonal profiles are generated through a mechanism involving the transfer and homogenization of cuticular hydrocarbons (CHCs) across members of the colony. However, how colony-specific chemical profiles are generated in other social insect clades remains mostly unknown. Here we show that in the honey bee (Apis mellifera), the colony-specific CHC profile completes its maturation in foragers via a sequence of stereotypic age-dependent quantitative and qualitative chemical transitions, which are driven by environmentally-sensitive intrinsic biosynthetic pathways. Therefore, the CHC profiles of individual honey bees are not likely produced through homogenization and transfer mechanisms, but instead mature in association with age-dependent division of labor. Furthermore, non-nestmate rejection behaviors seem to be contextually restricted to behavioral interactions between entering foragers and guards at the hive entrance.

Tissue-Specific cis-Regulatory Divergence Implicates eloF in Inhibiting Interspecies Mating in Drosophila.

Reproductive isolation is a key component of speciation. In many insects, a major driver of this isolation is cuticular hydrocarbon pheromones, which help to identify potential intraspecific mates [1-3]. When the distributions of related species overlap, there may be strong selection on mate choice for intraspecific partners [4-9] because interspecific hybridization carries significant fitness costs [10]. Drosophila has been a key model for the investigation of reproductive isolation; although both male and female mate choices have been extensively investigated [6, 11-16], the genes underlying species recognition remain largely unknown. To explore the molecular mechanisms underlying Drosophila speciation, we measured tissue-specific cis-regulatory divergence using RNA sequencing (RNA-seq) in D. simulans × D. sechellia hybrids. By focusing on cis-regulatory changes specific to female oenocytes, the tissue that produces cuticular hydrocarbons, we rapidly identified a small number of candidate genes. We found that one of these, the fatty acid elongase eloF, broadly affects the hydrocarbons present on D. sechellia and D. melanogaster females, as well as the propensity of D. simulans males to mate with them. Therefore, cis-regulatory changes in eloF may be a major driver in the sexual isolation of D. simulans from multiple other species. Our RNA-seq approach proved to be far more efficient than quantitative trait locus (QTL) mapping in identifying candidate genes; the same framework can be used to pinpoint candidate drivers of cis-regulatory divergence in traits differing between any interfertile species.

Neural circuits: anatomy of a sexual behavior.

Females of many species, once mated, undergo a rapid change in reproductive physiology and behavior, shifting from a sexually receptive state to one devoted to the rearing of offspring. Two recent reports shed light on the neural circuitry governing the female post-mating response in the fruit fly Drosophila, providing insight into the neurobiological processes governing a complex behavior.

Pigment-dispersing factor modulates pheromone production in clock cells that influence mating in drosophila.

Social cues contribute to the circadian entrainment of physiological and behavioral rhythms. These cues supplement the influence of daily and seasonal cycles in light and temperature. In Drosophila, the social environment modulates circadian mechanisms that regulate sex pheromone production and mating behavior. Here we demonstrate that a neuroendocrine pathway, defined by the neuropeptide Pigment-Dispersing Factor (PDF), couples the CNS to the physiological output of peripheral clock cells that produce pheromones, the oenocytes. PDF signaling from the CNS modulates the phase of the oenocyte clock. Despite its requirement for sustaining free-running locomoter activity rhythms, PDF is not necessary to sustain molecular rhythms in the oenocytes. Interestingly, disruption of the PDF signaling pathway reduces male sex pheromones and results in sex-specific differences in mating behavior. Our findings highlight the role of neuropeptide signaling and the circadian system in synchronizing the physiological and behavioral processes that govern social interactions.

Dissection of oenocytes from adult Drosophila melanogaster.

In Drosophila melanogaster, as in other insects, a waxy layer on the outer surface of the cuticle, composed primarily of hydrocarbon compounds, provides protection against desiccation and other environmental challenges. Several of these cuticular hydrocarbon (CHC) compounds also function as semiochemical signals, and as such mediate pheromonal communications between members of the same species, or in some instances between different species, and influence behavior. Specialized cells referred to as oenocytes are regarded as the primary site for CHC synthesis. However, relatively little is known regarding the involvement of the oenocytes in the regulation of the biosynthetic, transport, and deposition pathways contributing to CHC output. Given the significant role that CHCs play in several aspects of insect biology, including chemical communication, desiccation resistance, and immunity, it is important to gain a greater understanding of the molecular and genetic regulation of CHC production within these specialized cells. The adult oenocytes of D. melanogaster are located within the abdominal integument, and are metamerically arrayed in ribbon-like clusters radiating along the inner cuticular surface of each abdominal segment. In this video article we demonstrate a dissection technique used for the preparation of oenocytes from adult D. melanogaster. Specifically, we provide a detailed step-by-step demonstration of (1) how to fillet prepare an adult Drosophila abdomen, (2) how to identify the oenocytes and discern them from other tissues, and (3) how to remove intact oenocyte clusters from the abdominal integument. A brief experimental illustration of how this preparation can be used to examine the expression of genes involved in hydrocarbon synthesis is included. The dissected preparation demonstrated herein will allow for the detailed molecular and genetic analysis of oenocyte function in the adult fruit fly.

Biological rhythms: the taste-time continuum.

The gustatory system allows the fly to assess food quality, eliciting either acceptance or avoidance behaviors. A new study demonstrates that circadian clocks in gustatory receptor neurons regulate rhythms in taste sensitivity, drive rhythms in appetitive behavior and influence feeding.

Specialized cells tag sexual and species identity in Drosophila melanogaster.

Social interactions depend on individuals recognizing each other, and in this context many organisms use chemical signals to indicate species and sex. Cuticular hydrocarbon signals are used by insects, including Drosophila melanogaster, to distinguish conspecific individuals from others. These chemicals also contribute to intraspecific courtship and mating interactions. However, the possibility that sex and species identification are linked by common chemical signalling mechanisms has not been formally tested. Here we provide direct evidence that a single compound is used to communicate female identity among D. melanogaster, and to define a reproductive isolation barrier between D. melanogaster and sibling species. A transgenic manipulation eliminated cuticular hydrocarbons by ablating the oenocytes, specialized cells required for the expression of these chemical signals. The resulting oenocyte-less (oe(-)) females elicited the normal repertoire of courtship behaviours from males, but were actually preferred over wild-type females by courting males. In addition, wild-type males attempted to copulate with oe(-) males. Thus, flies lacking hydrocarbons are a sexual hyperstimulus. Treatment of virgin females with the aversive male pheromone cis-vaccenyl acetate (cVA) significantly delayed mating of oe(-) females compared to wild-type females. This difference was eliminated when oe(-) females were treated with a blend of cVA and the female aphrodisiac (7Z,11Z)-heptacosadiene (7,11-HD), showing that female aphrodisiac compounds can attenuate the effects of male aversive pheromones. 7,11-HD also was shown to have a crucial role in heterospecific encounters. Specifically, the species barrier was lost because males of other Drosophila species courted oe(-) D. melanogaster females, and D. simulans males consistently mated with them. Treatment of oe(-) females with 7,11-HD restored the species barrier, showing that a single compound can confer species identity. These results identify a common mechanism for sexual and species recognition regulated by cuticular hydrocarbons.

Social experience modifies pheromone expression and mating behavior in male Drosophila melanogaster.

BACKGROUND: The social life of animals depends on communication between individuals. Recent studies in Drosophila melanogaster demonstrate that various behaviors are influenced by social interactions. For example, courtship is a social interaction mediated by pheromonal signaling that occurs more frequently during certain times of the day than others. In adult flies, sex pheromones are synthesized in cells called oenocytes and displayed on the surface of the cuticle. Although the role of Drosophila pheromones in sexual behavior is well established, little is known about the timing of these signals or how their regulation is influenced by the presence of other flies. RESULTS: We report that oenocytes contain functional circadian clocks that appear to regulate the synthesis of pheromones by controlling the transcription of desaturase1 (desat1), a gene required for production of male cuticular sex pheromones. Moreover, levels of these pheromones vary throughout the day in a pattern that depends on the clock genes and most likely also depends on the circadian control of desat1 in the oenocytes. To assess group dynamics, we manipulated the genotypic composition of social groups (single versus mixed genotypes). This manipulation significantly affects clock gene transcription both in the head and oenocytes, and it also affects the pattern of pheromonal accumulation on the cuticle. Remarkably, we found that flies in mixed social groups mate more frequently than do their counterparts in uniform groups. CONCLUSIONS: These results demonstrate that social context exerts a regulatory influence on the expression of chemical signals, while modulating sexual behavior in the fruit fly.

Identification of genetic loci that interact with cut during Drosophila wing-margin development.

The Drosophila selector gene cut is a hierarchal regulator of external sensory organ identity and is required to pattern the sensory and nonsensory cells of the wing margin. Cut performs the latter function, in part, by maintaining expression of the secreted morphogen encoded by wingless (wg). We find that Cut is required for wing-margin sensory organ specification in addition to and independently of Wg maintenance. In addition, we performed a genetic modifier screen to identify other genes that interact with cut in the regulation of wing-margin patterning. In total, 45 genetic loci (35 gain-of-function and 10 loss-of-function loci) were identified by virtue of their ability to suppress the wing-margin defects resulting from gypsy retrotransposon-mediated insulation of the cut wing-margin enhancer. Further genetic characterization identified several subgroups of candidate cut interacting loci. One group consists of putative regulators of gypsy insulator activity. A second group is potentially required for the regulation of Cut expression and/or activity and includes longitudinals lacking, a gene that encodes a family of BTB-domain zinc-finger transcription factors. A third group, which includes a component of the Brahma chromatin remodeling complex encoded by moira, affects the level of Cut expression in two opposing ways by suppressing the gypsy-mediated ct(K) phenotype and enhancing the non-gypsy ct(53d) phenotype. This suggests that the Brahma complex modulates both enhancer-controlled transcription and gypsy-mediated gene insulation of the cut locus.