Ecology and Evolution of Communication in Social Insects

Deciphering the variation in cuticular hydrocarbon profiles of six European honey bee subspecies

The Western honey bee (Apis mellifera) subspecies exhibit local adaptive traits that evolved in response to the different environments that characterize their native distribution ranges. An important trait is the cuticular hydrocarbon (CHC) profile, which helps to prevent desiccation and mediate communication. We compared the CHC profiles of six European subspecies (A. m. mellifera, A. m. carnica, A. m. ligustica, A. m. macedonica, A. m. iberiensis, and A. m. ruttneri) and investigated potential factors shaping their composition. We did not find evidence of adaptation of the CHC profiles of the subspecies to the climatic conditions in their distribution range. Subspecies-specific differences in CHC composition might be explained by phylogenetic constraints or genetic drift. The CHC profiles of foragers were more subspecies-specific than those of nurse bees, while the latter showed more variation in their CHC profiles, likely due to the lower desiccation stress exerted by the controlled environment inside the hive. The strongest profile differences appeared between nurse bees and foragers among all subspecies, suggesting an adaptation to social task and a role in communication. Foragers also showed an increase in the relative amount of alkanes in their profiles compared to nurses, indicating adaptation to climatic conditions.

Ecological principles for the evolution of communication in collective systems

Communication allows members of a collective to share information about their environment. Advanced collective systems, such as multicellular organisms and social insect colonies, vary in whether they use communication at all and, if they do, in what types of signals they use, but the origins of these differences are poorly understood. Here, we develop a theoretical framework to investigate the evolution and diversity of communication strategies under collective-level selection. We find that whether communication can evolve depends on a collective's external environment: communication only evolves in sufficiently stable environments, where the costs of sensing are high enough to disfavour independent sensing but not so high that the optimal strategy is to ignore the environment altogether. Moreover, we find that the evolution of diverse signalling strategies-including those relying on prolonged signalling (e.g. honeybee waggle dance), persistence of signals in the environment (e.g. ant trail pheromones) and brief but frequent communicative interactions (e.g. ant antennal contacts)-can be explained theoretically in terms of the interplay between the demands of the environment and internal constraints on the signal. Altogether, we provide a general framework for comparing communication strategies found in nature and uncover simple ecological principles that may contribute to their diversity.

The scent of offspring: chemical profiles of larvae change during development and affect parental behavior in a burying beetle

Chemical cues and signals, especially in insects, play a pivotal role in mediating interactions between individuals. Past studies have largely focused on adult semiochemicals and have neglected those of juvenile stages. Especially in the context of parental care, the larval odor might have a profound impact on parenting behavior, guiding parents in how much resources they should allocate to the different developmental stages. However, whether ontogenetic changes occur in subsocial species and whether larval-emitted scents influence parent-offspring interactions is largely unknown. Using 3 different sampling techniques, we analyzed the cuticular and VOC profile of the 3 larval instars of the burying beetle Nicrophorus vespilloides, which is known for its elaborate parental care. We found distinct differences in the cuticular and VOC profiles across the 3 larval stages. Second-instar larvae, which receive more frequent feedings from parents than the other larval stages, released greater amounts of acetophenone, methyl geranate, and octanoic acid isopropyl ester than the first and third instar. Additionally, using a newly developed bioassay with automated video tracking, we found that adding the odor of second-instar larvae to first-instar larvae increased the number of maternal feeding trips. Our results suggest that the odor produced by larvae plays an important role in mediating parent-offspring interactions. Given these findings, burying beetles might emerge as a promising candidate for identifying a potential begging pheromone.

Evolution of odorant receptor repertoires across Hymenoptera is not linked to the evolution of eusociality

Communication is essential for social organisms. In eusocial insects, olfaction facilitates communication and recognition between nestmates. The study of certain model organisms has led to the hypothesis that odorant receptors are expanded in eusocial Hymenoptera. This has become a widely mentioned idea in the literature, albeit with conflicting reports, and has not been tested with a broad comparative analysis. Here we combined existing genomic and new neuroanatomical data, including from an approximately 100 Myr old fossil ant, across a phylogenetically broad sample of hymenopteran lineages. We find no evidence that variation in the size and evolutionary tempo of odorant receptor repertoires is related to eusociality. Post hoc exploration of our data hinted at loss of flight as a possible factor shaping some of the variation in OR repertoires in Hymenoptera. Nevertheless, our analyses revealed a complex pattern of evolutionary variation, and raise new questions about the ecological, behavioural and social factors that shape olfactory abilities.

Silencing the odorant co-receptor (Orco) in Anoplophora glabripennis disrupts responses to pheromones and host volatiles

Insects rely primarily on a robust and precise olfactory recognition system to detect chemicals and environmental signals. Olfaction is mediated mainly by various odorant receptors (ORs) expressed on olfactory neurons. The odorant co-receptor (Orco) is a highly conserved and obligatory subunit of ORs, and its combination with conventional ORs to form ligand-gated ion channel heterodimeric complexes plays a crucial role in odor recognition. Anoplophora glabripennis Is a major quarantinable pest that affects broadleaved tree species worldwide. Odorant binding proteins (OBPs) and ORs have been identified in the A. glabripennis genome and the binding properties of some OBPs and their cognate ligands have been clarified. The role of the OR-mediated recognition pathway, however, remains largely uncharacterized. Here, we cloned and sequenced the full-length Orco gene sequence of A. glabripennis and performed structural characterization of the protein. We found that AglaOrco has high sequence homology with Orco from other orders of insects, and that it is highly conserved. Spatio-temporal differential expression analysis revealed that AglaOrco is highly expressed in adult antennae, and that expression at the sexually mature stage is significantly higher than at other developmental stages. There was no significant difference in expression between sexes. Silence AglaOrco using RNAi revealed that expression levels of AglaOrco mRNA fell significantly in both males and females at 72 h post-injection of 5 μg of dsOrco, with no obvious effect on expression of most other olfactory-related genes; however, some were up-or downregulated. For example, silenced Orco-expressing males and females showed a significant reduction in antennal potential responses to the odorants 3-carene, Ocimene, and 4-heptyloxy-1-butanol. Overall, the data suggest that AglaOrco plays an important role in mediating olfactory perception in A. glabripennis, and also identifies potential target genes for environmentally friendly pest control strategies.

Low Intraspecific Aggression Level, Cuticular Hydrocarbons, and Polydomy in the Bullet Ant

Ants use chemical cues known as cuticular hydrocarbons (CHCs) for both intraspecific and interspecific recognition. These compounds serve ants in distinguishing between nestmates and non-nestmates, enabling them to coexist in polydomous colonies characterized by socially connected yet spatially separated nests. Hence, the aim of this study was to investigate the intraspecific aggression level between nestmates and non-nestmates of the bullet ant Paraponera clavata (Fabricius, 1775), analyze and compare their CHCs, and evaluate the occurrence of polydomy in this species. We conducted aggression tests between foragers, both in laboratory and field settings. To identify the chemical profiles, we utilized gas chromatography coupled with mass spectrometry (GC-MS). We marked the foragers found at nest entrances and subsequently recaptured these marked ants to validate workers exchange among nests. Across all nests, a low intraspecific aggression level was observed within the same area. However, a significant difference in aggression correlated to distance between nests. Analysis of the cuticular chemical profile of P. clavata unveiled colony-specific CHCs, both qualitatively and quantitatively. Notably, we observed instances of ants from certain nests entering or exiting different nests. This behavior, in conjunction with the observed low intraspecific aggression despite differences in CHCs suggests polydomy for this species. Polydomy can offer several benefits, including risk spreading, efficient exploitation of resources, potential for colony size increasing and reduced costs associated with foraging and competition.

Chemical and transcriptomic diversity do not correlate with ascending levels of social complexity in the insect order Blattodea

Eusocial insects, such as ants and termites, are characterized by high levels of coordinated social organization. This is contrasted by solitary insects that display more limited forms of collective behavior. It has been hypothesized that this gradient in sociobehavioral sophistication is positively correlated with chemical profile complexity, due to a potentially increased demand for diversity in chemical communication mechanisms in insects with higher levels of social complexity. However, this claim has rarely been assessed empirically. Here, we compare different levels of chemical and transcriptomic complexity in selected species of the order Blattodea that represent different levels of social organization, from solitary to eusocial. We primarily focus on cuticular hydrocarbon (CHC) complexity, since it has repeatedly been demonstrated that CHCs are key signaling molecules conveying a wide variety of chemical information in solitary as well as eusocial insects. We assessed CHC complexity and divergence between our studied taxa of different social complexity levels as well as the differentiation of their respective repertoires of CHC biosynthesis gene transcripts. Surprisingly, we did not find any consistent pattern of chemical complexity correlating with social complexity, nor did the overall chemical divergence or transcriptomic repertoire of CHC biosynthesis genes reflect on the levels of social organization. Our results challenge the assumption that increasing social complexity is generally reflected in more complex chemical profiles and point toward the need for a more cautious and differentiated view on correlating complexity on a chemical, genetic, and social level.

Social evolution: Limb amputation prevents infection in ants

Social insect workers, renowned for their altruism, are frequently perceived as 'disposable'. A new study finds that ants amputate the limbs of nestmates, which saves them from infection, and indicates that worker care is as critical to colony success as sacrifice.

Genomic basis of adaptation to climate and parasite prevalence and the importance of odorant perception in the ant Temnothorax longispinosus

A co-evolutionary arms race ensues when parasites exhibit exploitative behaviour, which prompts adaptations in their hosts, in turn triggering counter-adaptations by the parasites. To unravel the genomic basis of this coevolution from the host's perspective, we collected ants of the host species Temnothorax longispinosus, parasitized by the social parasite Temnothorax americanus, from 10 populations in the northeastern United States exhibiting varying levels of parasite prevalence and living under different climatic conditions. We conducted a genome-wide association study (GWAS) to identify single nucleotide polymorphisms (SNPs) associated with both prevalence and climate. Our investigation highlighted a multitude of candidate SNPs associated with parasite prevalence, particularly in genes responsible for sensory perception of smell including odorant receptor genes. We further focused on population-specific compositions of cuticular hydrocarbons, a complex trait important for signalling, communication and protection against desiccation. The relative abundances of n-alkanes were correlated with climate, while there was only a trend between parasite prevalence and the relative abundances of known recognition cues. Furthermore, we identified candidate genes likely involved in the synthesis and recognition of specific hydrocarbons. In addition, we analysed the population-level gene expression in the antennae, the primary organ for odorant reception, and established a strong correlation with parasite prevalence. Our comprehensive study highlights the intricate genomic patterns forged by the interplay of diverse selection factors and how these are manifested in the expression of various phenotypes.

Cuticular extracts induce aggregation in head lice

The human head lice Pediculus humanus capitis (De Geer) (Phthiraptera: Pediculidae) are strict, obligate human ectoparasites that spends their entire life cycle in the host and cause skin irritation and derived infections. Despite the health-related importance, few studies have evaluated the chemical communication among these insects. Here, we evaluate the response of lice of both sexes to cuticular extracts using two solvents of different polarity (hexane and methanol). Cuticular extracts that elicited an attraction response towards head lice were analysed by gas chromatography-mass spectrometry (GC-MS) to determine the cuticular lipid profile. Both lice sexes were attracted to the hexane extracts but not the methanol extracts, suggesting the non-polarity of the compounds present in the cuticle. Chemical analyses of hexane extracts from males and females showed high similarity in major compounds. This study provides the first evidence that lice respond to cuticle extracts, which may be important to understand aggregation behaviour.

Innate and learned components of egg recognition in the ant Camponotus floridanus

Insect societies discriminate against foreigners to avoid exploitation. In ants, helper workers only accept individuals with the familiar chemical cues of their colony. Similarly, unfamiliar eggs may get rejected at their first appearance in the nest. We investigated egg acceptance mechanisms by introducing different types of foreign eggs into worker groups of the ant Camponotus floridanus. Workers from established colonies familiar with queen-laid eggs always accepted eggs from highly fecund queens, but worker-laid eggs only after exposure for several weeks. Workers naive to eggs only rejected worker-laid eggs once they had prior exposure to eggs laid by highly fecund queens, suggesting that prior exposure to such eggs is necessary for discrimination. The general acceptance of eggs from highly fecund queens, irrespective of previous worker egg exposure, suggests an innate response to the queen pheromone these eggs carry. Workers learned to accept queen-laid eggs from different species, indicating high flexibility in learning egg-recognition cues. In incipient colonies with queen-laid eggs that carry a weak queen pheromone, worker-laid eggs were more likely to get accepted than queen-laid eggs from a different species, suggesting that the similarity of egg-recognition cues between the two types of C. floridanus eggs increases acceptance.

Courtship song differs between African and European populations of Drosophila melanogaster and involves a strong effect locus

The courtship song of Drosophila melanogaster has long served as excellent model system for studies of animal communication and differences in courtship song have been demonstrated among populations and between species. Here, we report that flies of African and European origin, which diverged approximately 13,000 years ago, show significant genetic differentiation in the use of slow versus fast pulse song. Using a combination of quantitative trait mapping and population genetic analysis we detected a single strong QTL underlying this trait and we identified candidate genes that may contribute to the evolution of this trait. Song trait variation between parental strains of our recombinant inbred panel enabled detection of genomic intervals associated with six additional song traits, some of which include known courtship-related genes. These findings improve the prospects for further genetic insights into the evolution of reproductive behavior and the biology underlying courtship song.

Chemical Profiles Differ between Communal Breeding Groups in a Highly Social Bird

AbstractGregarious species must distinguish group members from nongroup members. Olfaction is important for group recognition in social insects and mammals but rarely studied in birds, despite birds using olfaction in social contexts from species discrimination to kin recognition. Olfactory group recognition requires that groups have a signature odor, so we tested for preen oil and feather chemical similarity in group-living smooth-billed anis (Crotophaga ani). Physiology affects body chemistry, so we also tested for an effect of egg-laying competition, as a proxy for reproductive status, on female chemical similarity. Finally, the fermentation hypothesis for chemical recognition posits that host-associated microbes affect host odor, so we tested for covariation between chemicals and microbiota. Group members were more chemically similar across both body regions. We found no chemical differences between sexes, but females in groups with less egg-laying competition had more similar preen oil, suggesting that preen oil contains information about reproductive status. There was no overall covariation between chemicals and microbes; instead, subsets of microbes could mediate olfactory cues in birds. Preen oil and feather chemicals showed little overlap and may contain different information. This is the first demonstration of group chemical signatures in birds, a finding of particular interest given that smooth-billed anis live in nonkin breeding groups. Behavioral experiments are needed to test whether anis can distinguish group members from nongroup members using odor cues.

The tri-flow adaptiveness of codes in major evolutionary transitions

Life codes increase in both number and variety with biological complexity. Although our knowledge of codes is constantly expanding, the evolutionary progression of organic, neural, and cultural codes in response to selection pressure remains poorly understood. Greater clarification of the selective mechanisms is achieved by investigating how major evolutionary transitions reduce spatiotemporal and energetic constraints on transmitting heritable code to offspring. Evolution toward less constrained flows is integral to enduring flow architecture everywhere, in both engineered and natural flow systems. Beginning approximately 4 billion years ago, the most basic level for transmitting genetic material to offspring was initiated by protocell division. Evidence from ribosomes suggests that protocells transmitted comma-free or circular codes, preceding the evolution of standard genetic code. This rudimentary information flow within protocells is likely to have first emerged within the geo-energetic and geospatial constraints of hydrothermal vents. A broad-gauged hypothesis is that major evolutionary transitions overcame such constraints with tri-flow adaptations. The interconnected triple flows incorporated energy-converting, spatiotemporal, and code-based informational dynamics. Such tri-flow adaptations stacked sequence splicing code on top of protein-DNA recognition code in eukaryotes, prefiguring the transition to sexual reproduction. Sex overcame the spatiotemporal-energetic constraints of binary fission with further code stacking. Examples are tubulin code and transcription initiation code in vertebrates. In a later evolutionary transition, language reduced metabolic-spatiotemporal constraints on inheritance by stacking phonetic, phonological, and orthographic codes. In organisms that reproduce sexually, each major evolutionary transition is shown to be a tri-flow adaptation that adds new levels of code-based informational exchange. Evolving biological complexity is also shown to increase the nongenetic transmissibility of code.

Neuroregulation of foraging behavior mediated by the olfactory co-receptor Orco in termites

Olfaction is critical for survival because it allows animals to look for food and detect pheromonal cues. Neuropeptides modulate olfaction and behaviors in insects. While how the neuroregulation of olfactory recognition affects foraging behavior in termites is still unclear. Here, we analyzed the change after silencing the olfactory co-receptor gene (Orco) and the neuropeptide Y gene (NPY), and then investigated the impact of olfactory recognition on foraging behavior in Odontotermes formosanus under different predation pressures. The knockdown of Orco resulted in the reduced Orco protein expression in antennae and the decreased EAG response to trail pheromones. In addition, NPY silencing led to the damaged ability of olfactory response through downregulating Orco expression. Both dsOrco- and dsNPY-injected worker termites showed significantly reduced walking activity and foraging success. Additionally, we found that 0.1 pg/cm trail pheromone and nestmate soldiers could provide social buffering to relieve the adverse effect of predator ants on foraging behavior in worker termites with the normal ability of olfactory recognition. Our orthogonal experiments further verified that Orco/NPY genes are essential in manipulating termite olfactory recognition during foraging under different predation pressures, suggesting that the neuroregulation of olfactory recognition plays a crucial role in regulating termite foraging behavior.

The buzz within: the role of the gut microbiome in honeybee social behavior

Gut symbionts influence the physiology and behavior of their host, but the extent to which these effects scale to social behaviors is an emerging area of research. The use of the western honeybee (Apis mellifera) as a model enables researchers to investigate the gut microbiome and behavior at several levels of social organization. Insight into gut microbial effects at the societal level is critical for our understanding of how involved microbial symbionts are in host biology. In this Commentary, we discuss recent findings in honeybee gut microbiome research and synthesize these with knowledge of the physiology and behavior of other model organisms to hypothesize how host-microbe interactions at the individual level could shape societal dynamics and evolution.

Targeted treatment of injured nestmates with antimicrobial compounds in an ant society

Infected wounds pose a major mortality risk in animals. Injuries are common in the ant Megaponera analis, which raids pugnacious prey. Here we show that M. analis can determine when wounds are infected and treat them accordingly. By applying a variety of antimicrobial compounds and proteins secreted from the metapleural gland to infected wounds, workers reduce the mortality of infected individuals by 90%. Chemical analyses showed that wound infection is associated with specific changes in the cuticular hydrocarbon profile, thereby likely allowing nestmates to diagnose the infection state of injured individuals and apply the appropriate antimicrobial treatment. This study demonstrates that M. analis ant societies use antimicrobial compounds produced in the metapleural glands to treat infected wounds and reduce nestmate mortality.

Evolution of the neuronal substrate for kin recognition in social Hymenoptera

In evolutionary terms, life is about reproduction. Yet, in some species, individuals forgo their own reproduction to support the reproductive efforts of others. Social insect colonies for example, can contain up to a million workers that actively cooperate in tasks such as foraging, brood care and nest defence, but do not produce offspring. In such societies the division of labour is pronounced, and reproduction is restricted to just one or a few individuals, most notably the queen(s). This extreme eusocial organisation exists in only a few mammals, crustaceans and insects, but strikingly, it evolved independently up to nine times in the order Hymenoptera (including ants, bees and wasps). Transitions from a solitary lifestyle to an organised society can occur through natural selection when helpers obtain a fitness benefit from cooperating with kin, owing to the indirect transmission of genes through siblings. However, this process, called kin selection, is vulnerable to parasitism and opportunistic behaviours from unrelated individuals. An ability to distinguish kin from non-kin, and to respond accordingly, could therefore critically facilitate the evolution of eusociality and the maintenance of non-reproductive workers. The question of how the hymenopteran brain has adapted to support this function is therefore a fundamental issue in evolutionary neuroethology. Early neuroanatomical investigations proposed that social Hymenoptera have expanded integrative brain areas due to selection for increased cognitive capabilities in the context of processing social information. Later studies challenged this assumption and instead pointed to an intimate link between higher social organisation and the existence of developed sensory structures involved in recognition and communication. In particular, chemical signalling of social identity, known to be mediated through cuticular hydrocarbons (CHCs), may have evolved hand in hand with a specialised chemosensory system in Hymenoptera. Here, we compile the current knowledge on this recognition system, from emitted identity signals, to the molecular and neuronal basis of chemical detection, with particular emphasis on its evolutionary history. Finally, we ask whether the evolution of social behaviour in Hymenoptera could have driven the expansion of their complex olfactory system, or whether the early origin and conservation of an olfactory subsystem dedicated to social recognition could explain the abundance of eusocial species in this insect order. Answering this question will require further comparative studies to provide a comprehensive view on lineage-specific adaptations in the olfactory pathway of Hymenoptera.

Chemical Resemblance of Egg Surface Compounds and Dufour's Gland in Two Neotropical Polistinae Wasps Polistes versicolor (Olivier) and Mischocyttarus metathoracicus (de Saussure, 1854)

Chemical communication plays a major role in regulating social dynamics in social insect colonies. The most studied class of chemical compounds are the cuticular hydrocarbons (CHCs), compounds with high molecular weight that cover the insect body. CHCs are used in nestmate recognition and to signal reproductive status. Brood, in the form of larvae and eggs, is known to participate in chemical communication and social dynamics by performing hunger behaviour and inducing interaction with adults and conferring nest and maternity identity. CHCs of adults and egg surface compounds are similar in composition in social insect species. The main source of egg compounds is proposed to be Dufour's gland, an accessory reproductive gland found in several Hymenoptera females. There is still a lack of information about the level of similarity among CHCs, compounds of egg surface and Dufour's gland for several wasp species, which could provide correlational evidence about the origins of egg-marking compounds. Thus, we investigated whether egg surface compounds were more similar to CHCs or Dufour's gland secretions in two Neotropical primitively eusocial wasp species, Polistes versicolor (Olivier) and Mischocyttarus metathoracicus (de Saussure, 1854). As expected, there was a higher chemical similarity between eggs and Dufour's gland secretions in both studied species, supporting the hypothesis that this gland is the source of chemical compounds found over the eggs in these two primitively eusocial species.

S-dinotefuran affects the social behavior of honeybees (Apis mellifera)and increases their risk in the colony

The toxic effects of neonicotinoid pesticides on honeybees is a global concern, whereas little is known about the effect of stereoisomeric pesticides among honeybee social behavior. In this study, we investigated the effects of stereoisomeric dinotefuran on honeybee social behavior. We found that honeybees exhibit a preference for consuming food containing S-dinotefuran, actively engage in trophallaxis with S-dinotefuran-consuming peers, and consequently acquire higher levels of S-dinotefuran compared with R-dinotefuran. In comparison to R-dinotefuran, S-dinotefuran stimulates honeybees to elevate their body temperature, thereby attracting more peers for trophallaxis. Transcriptome analysis revealed a significant enrichment of thermogenesis pathways due to S-dinotefuran exposure. Additionally, metabolome data indicated that S-dinotefuran may enhance body temperature by promoting lipid synthesis in the lysine degradation pathway. Consequently, body temperature emerges as a key factor influencing honeybee social behavior. Our study is the first to highlight the propensity of S-dinotefuran to raise honeybee body temperature, which prompts honeybee to preferentially engage in trophallaxis with peers exhibiting higher body temperatures. This preference may lead honeybees to collect more dinotefuran-contaminated food in the wild, significantly accelerating dinotefuran transmission within a population. Proactive trophallaxis further amplifies the risk of neonicotinoid pesticide transmission within a population, making honeybees that have consumed S-dinotefuran particularly favored within their colonies. These findings may contribute to our understanding of the higher risk associated with neonicotinoid use compared with other pesticides.

Termite cuticular extracts improve acceptance of bait for controlling invasive Asian needle ants, Brachyponera chinensis

BACKGROUND

The Asian needle ant, Brachyponera chinensis, is an invasive ant currently spreading in urban and natural habitats throughout the eastern United States. Recent studies have documented the negative impact of B. chinensis on native ecosystems and human health, yet effective control strategies are lacking. Control difficulties are, in part, due to the unique biology of B. chinensis, which is a predatory ant and a termite specialist. Given that subterranean termites are an important nutritional resource for B. chinensis, the current study evaluated the potential of termite cuticular extract to improve the target-specificity and efficacy of commercial bait used for B. chinensis control.

RESULTS

The efficacy of bait augmented with termite cuticular extracts was evaluated in laboratory and field trials. In laboratory assays, B. chinensis colonies were offered granular bait treated with termite cuticular extract. Results demonstrated that the acceptance of commercial bait is significantly increased by the addition of termite cuticular extract or synthetic (Z)-9-pentacosene, a major component of termite cuticular extract. Foraging activity of Asian needle ants was significantly greater on baits augmented with termite cuticular extract or (Z)-9-pentacosene relative to standard bait. Furthermore, bait augmented with termite cuticular extract worked substantially faster relative to standard bait. To evaluate population effects, field studies were conducted in forested areas invaded by B. chinensis. Bait treated with termite cuticular extract scattered on the forest floor provided rapid control of B. chinensis and ant densities throughout the treated plots declined by 98% within 14 days.

CONCLUSION

The incorporation of termite cuticular extracts and individual cuticular hydrocarbons such as (Z)-9-pentacosene into traditional baits used for B. chinensis control may offer a novel tool to manage this increasingly problematic invasive ant. © 2023 The Author. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Past, Present, and Future of Human Chemical Communication Research

Although chemical signaling is an essential mode of communication in most vertebrates, it has long been viewed as having negligible effects in humans. However, a growing body of evidence shows that the sense of smell affects human behavior in social contexts ranging from affiliation and parenting to disease avoidance and social threat. This article aims to (a) introduce research on human chemical communication in the historical context of the behavioral sciences; (b) provide a balanced overview of recent advances that describe individual differences in the emission of semiochemicals and the neural mechanisms underpinning their perception, that together demonstrate communicative function; and (c) propose directions for future research toward unraveling the molecular principles involved and understanding the variability in the generation, transmission, and reception of chemical signals in increasingly ecologically valid conditions. Achieving these goals will enable us to address some important societal challenges but are within reach only with the aid of genuinely interdisciplinary approaches.

Postural analysis reveals persistent changes in paper wasp foundress behavioral state after conspecific challenge

Vigilant animals detect and respond to threats in the environment, often changing posture and movement patterns. Vigilance is modulated not only by predators but also by conspecific threats. In social animals, precisely how conspecific threats alter vigilance behavior over time is relevant to long-standing hypotheses about social plasticity. We report persistent effects of a simulated conspecific challenge on behavior of wild northern paper wasp foundresses, Polistes fuscatus. During the founding phase of the colony cycle, conspecific wasps can usurp nests from the resident foundress, representing a severe threat. We used automated tracking to monitor the movement and posture of P. fuscatus foundresses in response to simulated intrusions. Wasps displayed increased movement, greater bilateral wing extension, and reduced antennal separation after the threat was removed. These changes were not observed after presentation with a wooden dowel. By rapidly adjusting individual behavior after fending off an intruder, paper wasp foundresses might invest in surveillance of potential threats, even when such threats are no longer immediately present. The prolonged vigilance-like behavioral state observed here is relevant to plasticity of social recognition processes in paper wasps.

Decoding the genetic and chemical basis of sexual attractiveness in parasitic wasps

Attracting and securing potential mating partners is of fundamental importance for reproduction. Therefore, signaling sexual attractiveness is expected to be tightly coordinated in communication systems synchronizing senders and receivers. Chemical signaling has permeated through all taxa of life as the earliest and most widespread form of communication and is particularly prevalent in insects. However, it has been notoriously difficult to decipher how exactly information related to sexual signaling is encoded in complex chemical profiles. Similarly, our knowledge of the genetic basis of sexual signaling is very limited and usually restricted to a few case studies with comparably simple pheromonal communication mechanisms. The present study jointly addresses these two knowledge gaps by characterizing two fatty acid synthase genes that most likely evolved by tandem gene duplication and that simultaneously impact sexual attractiveness and complex chemical surface profiles in parasitic wasps. Gene knockdown in female wasps dramatically reduces their sexual attractiveness coinciding with a drastic decrease in male courtship and copulation behavior. Concordantly, we found a striking shift of methyl-branching patterns in the female surface pheromonal compounds, which we subsequently demonstrate to be the main cause for the greatly reduced male mating response. Intriguingly, this suggests a potential coding mechanism for sexual attractiveness mediated by specific methyl-branching patterns in complex cuticular hydrocarbon (CHC) profiles. So far, the genetic underpinnings of methyl-branched CHCs are not well understood despite their high potential for encoding information. Our study sheds light on how biologically relevant information can be encoded in complex chemical profiles and on the genetic basis of sexual attractiveness.

Building Resilient Healthcare Teams: Insights from Analogy to the Social Biology of Ants, Honey Bees and Other Social Insects

The resilience of a healthcare system hinges on the adaptability of its teams. Thus far, healthcare teams have relied on well-defined scopes of practice to fulfill their safety mandate. While this feature has proven effective when dealing with stable situations, when it comes to disruptive events, healthcare teams find themselves navigating a fine balance between safety and resilience. Therefore, a better understanding of how the safety vs resilience trade-off varies under different circumstances is necessary if we are to promote and better train for resilience in modern healthcare teams. In this paper, we aim to bring awareness to the sociobiology analogy that healthcare teams might find useful during moments when safety and adaptability have the potential to conflict. Three principles underpin the sociobiology analogy: communication, decentralization, and plasticity. Of particular interest in this paper is plasticity whereby swapping roles or tasks becomes an adaptive, rather than a maladaptive, response teams could embrace when facing disruptive situations. While plasticity has naturally evolved in social insects, infusing plasticity in healthcare teams requires intentional training. Inspired by the sociobiology analogy, such training must value the ability: a) to read each other's cues and miscues, b) to step aside when others had the necessary skills, even if outside their scope, c) to deviate from protocols, and d) to foster cross-training. If the goal is to increase a team's behavioural flexibility and boost their resilience, this training mindset should become second nature.

Basic Structures of Gut Bacterial Communities in Eusocial Insects

Gut bacterial communities assist host animals with numerous functions such as food digestion, nutritional provision, or immunity. Some social mammals and insects are unique in that their gut microbial communities are stable among individuals. In this review, we focus on the gut bacterial communities of eusocial insects, including bees, ants, and termites, to provide an overview of their community structures and to gain insights into any general aspects of their structural basis. Pseudomonadota and Bacillota are prevalent bacterial phyla commonly detected in those three insect groups, but their compositions are distinct at lower taxonomic levels. Eusocial insects harbor unique gut bacterial communities that are shared within host species, while their stability varies depending on host physiology and ecology. Species with narrow dietary habits, such as eusocial bees, harbor highly stable and intraspecific microbial communities, while generalists, such as most ant species, exhibit relatively diverse community structures. Caste differences could influence the relative abundance of community members without significantly altering the taxonomic composition.

How to perceive the insecticide? The Neotropical termite Nasutitermes corniger (Termitidae: Nasutitermitinae) triggers alert behavior after exposure to imidacloprid

In eusocial insects, alarm signaling is used to inform nestmates about threats such as predators, competitors, and pathogens. Such behavior is important for the survival of colonies. However, studies evaluating the effect of insecticides on the alarm in termites have not yet been reported. Here, we inspected the effects of insecticide on alarm communication in Nasutitermes corniger. Specifically, we test the following hypotheses: (1) termite groups exposed to insecticide imidacloprid increase the body shaking movements, displaying an alert behavior; and (2) the alert behavior displayed after exposition to insecticide is dose dependent. Bioassays were conducted evaluating the body shaking movements and walking activity of termite groups exposed and non-exposed to insecticide. Thereafter, body shaking movements were evaluated in groups submitted to different doses of insecticide. In general, exposing termite groups to insecticide resulted in significantly higher body shaking movements compared to non-exposed groups. There was a positive effect of imidacloprid doses on the shaking movements. Walking activity, however, decreases in those groups exposed to the insecticide. Our results demonstrate the existence of 'insecticide alert behavior' in N. corniger and it appears to be a previously unrecognized communication mechanism in termites that allows for reducing the intoxication risks in the colony.

Body mass and cuticular hydrocarbon profiles, but not queen number, underlie worker desiccation resistance in a facultatively polygynous harvester ant (Pogonomyrmex californicus)

As small-bodied terrestrial organisms, insects face severe desiccation risks in arid environments, and these risks are increasing under climate change. Here, we investigate the physiological, chemical, and behavioral mechanisms by which harvester ants, one of the most abundant arid-adapted insect groups, cope with desiccating environmental conditions. We aimed to understand how body size, cuticular hydrocarbon profiles, and queen number impact worker desiccation resistance in the facultatively polygynous harvester ant, Pogonomyrmex californicus. We measured survival at 0% humidity of field-collected worker ants sourced from three closely situated populations within a semi-arid region of southern California. These populations vary in queen number, with one population dominated by multi-queen colonies (primary polygyny), one population dominated by single-queen colonies, and one containing an even mix of single- and multi-queen colonies. We found no effect of population on worker survival in desiccation assays, suggesting that queen number does not influence colony desiccation resistance. Across populations, however, body mass and cuticular hydrocarbon profiles significantly predicted desiccation resistance. Larger-bodied workers survived longer in desiccation assays, emphasizing the importance of reduced surface area-to-volume ratios in maintaining water balance. Additionally, we observed a positive relationship between desiccation resistance and the abundance of n-alkanes, supporting previous work that has linked these high-melting point compounds to improved body water conservation. Together, these results contribute to an emerging model explaining the physiological mechanisms of desiccation resistance in insects.

The Role of Biogenic Amines in Social Insects: With a Special Focus on Ants

Eusociality represents the higher degree of interaction in insects. This complex social structure is maintained through a multimodal communication system that allows colony members to be flexible in their responses, fulfilling the overall society's needs. The colony plasticity is supposedly achieved by combining multiple biochemical pathways through the neuromodulation of molecules such as biogenic amines, but the mechanisms through which these regulatory compounds act are far from being fully disentangled. Here, we review the potential function of major bioamines (dopamine, tyramine, serotine, and octopamine) on the behavioral modulation of principal groups of eusocial Hymenoptera, with a special focus on ants. Because functional roles are species- and context-dependent, identifying a direct causal relationship between a biogenic amine variation and behavioral changes is extremely challenging. We also used a quantitative and qualitative synthesis approach to summarize research trends and interests in the literature related to biogenic amines of social insects. Shedding light on the aminergic regulation of behavioral responses will pave the way for an entirely new approach to understanding the evolution of sociality in insects.

Multispecies collective waving behaviour in fish

Collective behaviour is widely accepted to provide a variety of antipredator benefits. Acting collectively requires not only strong coordination among group members, but also the integration of among-individual phenotypic variation. Therefore, groups composed of more than one species offer a unique opportunity to look into the evolution of both mechanistic and functional aspects of collective behaviour. Here, we present data on mixed-species fish shoals that perform collective dives. These repeated dives produce water waves capable of delaying and/or reducing the success of piscivorous bird attacks. The large majority of the fish in these shoals consist of the sulphur molly, Poecilia sulphuraria, but we regularly also found a second species, the widemouth gambusia, Gambusia eurystoma, making these shoals mixed-species aggregations. In a set of laboratory experiments, we found that gambusia were much less inclined to dive after an attack as compared with mollies, which almost always dive, though mollies dived less deep when paired with gambusia that did not dive. By contrast, the behaviour of gambusia was not influenced by the presence of diving mollies. The dampening effect of less responsive gambusia on molly diving behaviour can have strong evolutionary consequences on the overall collective waving behaviour as we expect shoals with a high proportion of unresponsive gambusia to be less effective at producing repeated waves. This article is part of a discussion meeting issue 'Collective behaviour through time'.

Volatile Organic Compounds: A Promising Tool for Bed Bug Detection

The recent decades' resurgence of bed bugs as a public health concern in industrialized countries has driven an increased interest on new sustainable insecticide-free methods to monitor and control these ectoparasites. Current methods of detection rely mainly on visual inspection or canine scent detection, which are methods that are time-consuming, require experience, are non-specific or require costly mission repetitions. Volatile organic compounds (VOCs) are considered an environmentally friendly alternative and a promising approach for bed bug detection. An overview of the released literature on VOCs, their chemical characteristics and their role in bed bugs' intra- and inter-species communications allowed us to highlight the identification of 49 VOCs in Cimex lectularius (23 molecules) and C. hemipterus (26), which are emitted by both sexes during diverse compartments including aggregation (46), mating (11), defense (4), etc., and all life stages including exuviae or dead bed bugs as a principal indicator of infestation. The latter has a great importance for application of these semiochemicals in successful detection and control management of bed bugs and to prevent their further dispersion. This approach has the advantage of more reliability compared to conventional detection methods with no need for repeated inspections, household furniture moving or resident rehousing for bed bugs' VOC detection, which are commonly performed by active or passive sampling with absorbing tubes and analyzed by gas chromatography-based analytical platforms.

Non-lethal fungal infection could reduce aggression towards strangers in ants

Many parasites interfere with the behaviour of their hosts. In social animals, such as ants, parasitic interference can cause changes on the level of the individual and also on the level of the society. The ant-parasitic fungus Rickia wasmannii influences the behaviour of Myrmica ants by expanding the host's nestmate recognition template, thereby increasing the chance of the colony accepting infected non-nestmates. Infected ants consistently show an increase of the alkane tricosane (n-C23) in their cuticular hydrocarbon profiles. Although experimental application of single compounds often elicits aggression towards manipulated ants, we hypothesized that the increase of n-C23 might underlie the facilitated acceptance of infected non-nestmates. To test this, we mimicked fungal infection in M. scabrinodis by applying synthetic n-C23 to fresh ant corpses and observed the reaction of infected and uninfected workers to control and manipulated corpses. Infected ants appeared to be more peaceful towards infected but not uninfected non-nestmates. Adding n-C23 to uninfected corpses resulted in reduced aggression in uninfected ants. This supports the hypothesis that n-C23 acts as a 'pacifying' signal. Our study indicates that parasitic interference with the nestmate discrimination of host ants might eventually change colony structure by increasing genetic heterogeneity in infected colonies.

Cuticular hydrocarbons of alpine bumble bees (Hymenoptera: Bombus) are species-specific, but show little evidence of elevation-related climate adaptation

Alpine bumble bees are the most important pollinators in temperate mountain ecosystems. Although they are used to encounter small-scale successions of very different climates in the mountains, many species respond sensitively to climatic changes, reflected in spatial range shifts and declining populations worldwide. Cuticular hydrocarbons (CHCs) mediate climate adaptation in some insects. However, whether they predict the elevational niche of bumble bees or their responses to climatic changes remains poorly understood. Here, we used three different approaches to study the role of bumble bees’ CHCs in the context of climate adaptation: using a 1,300 m elevational gradient, we first investigated whether the overall composition of CHCs, and two potentially climate-associated chemical traits (proportion of saturated components, mean chain length) on the cuticle of six bumble bee species were linked to the species’ elevational niches. We then analyzed intraspecific variation in CHCs of Bombus pascuorum along the elevational gradient and tested whether these traits respond to temperature. Finally, we used a field translocation experiment to test whether CHCs of Bombus lucorum workers change, when translocated from the foothill of a cool and wet mountain region to (a) higher elevations, and (b) a warm and dry region. Overall, the six species showed distinctive, species-specific CHC profiles. We found inter- and intraspecific variation in the composition of CHCs and in chemical traits along the elevational gradient, but no link to the elevational distribution of species and individuals. According to our expectations, bumble bees translocated to a warm and dry region tended to express longer CHC chains than bumble bees translocated to cool and wet foothills, which could reflect an acclimatization to regional climate. However, chain lengths did not further decrease systematically along the elevational gradient, suggesting that other factors than temperature also shape chain lengths in CHC profiles. We conclude that in alpine bumble bees, CHC profiles and traits respond at best secondarily to the climate conditions tested in this study. While the functional role of species-specific CHC profiles in bumble bees remains elusive, limited plasticity in this trait could restrict species’ ability to adapt to climatic changes.

A matter of the beehive sound: Can honey bees alert the pollution out of their hives?

Honey bees (Apis spp.) are often used as biological indicators of environmental changes. Recently, bees have been explored to monitor air contaminants by listening to the beehive sound. The beehive sound is believed to encode information on bee responses to chemicals outside their hives. Here we conducted an experiment to address this. First, we randomly fed colonies with pure syrup (PS), acetone-laced syrup (AS), or ethyl acetate-laced syrup (ES) in front of the beehives and collect the beehive sound. Based on the audio data, we build machine learning (ML) models to identify the types of syrup. The result shows that ML models achieved over 90% accuracy for identifying syrup types, indicating that the bees inside their hives emitted the sound associated with the chemicals outside their hives. Then, we sequentially fed the colonies in the order of PS, ES, and AS (the first session) and again in the reverse order (the second session), but did not remove the accumulated ES or AS in the alternative feeding experiment. Based on the audio data, the identification accuracy of both ES and AS by the ML model built on the randomly feeding experiment was different, indicating that the accumulated chemical residuals could confuse the ML models. Therefore, the beehive sound-based environmental monitoring should simultaneously consider the responses of bees to the chemicals outside their hives and their responses to those accumulated inside their hives, which may act simultaneously.

Alarm communication predates eusociality in termites

Termites (Blattodea: Isoptera) have evolved specialized defensive strategies for colony protection. Alarm communication enables workers to escape threats while soldiers are recruited to the source of disturbance. Here, we study the vibroacoustic and chemical alarm communication in the wood roach Cryptocercus and in 20 termite species including seven of the nine termite families, all life-types, and all feeding and nesting habits. Our multidisciplinary approach shows that vibratory alarm signals represent an ethological synapomorphy of termites and Cryptocercus. In contrast, chemical alarms have evolved independently in several cockroach groups and at least twice in termites. Vibroacoustic alarm signaling patterns are the most complex in Neoisoptera, in which they are often combined with chemical signals. The alarm characters correlate to phylogenetic position, food type and hardness, foraging area size, and nesting habits. Overall, species of Neoisoptera have developed the most sophisticated communication system amongst termites, potentially contributing to their ecological success.

Cuticular Hydrocarbon Polymorphism in a Parasitoid Wasp

Cuticular hydrocarbons (CHCs) are major constituents of the cuticular lipid layer of insects. They serve not only as a barrier to desiccation, but often additionally mediate communication at close range. The compositions of the CHC profiles, i.e., the specific compounds and their relative amounts, usually differ between species. Additional intraspecific variability can be found between different populations, between colonies and castes of social insects, and between the sexes. Thus, such groups can often be distinguished based on distinctive compounds and/or specific compound ratios. The CHC profile may further be influenced by biotic and abiotic factors, which therefore can impact, e.g., nestmate recognition or mate choice. However, consistent intrasexual variation seems to be rare. Here, we investigated a case of intrasexual CHC variability within a single population of a parasitoid wasp. While wasps of both sexes produced the same set of compounds, the relative amounts of specific compound classes revealed the presence of intrasexual chemical phenotypes. This is, to our knowledge, the first report of three distinct female CHC profile patterns within a population of a solitary insect that uses CHCs for mate recognition. Additionally, male CHC profiles, while overall very similar, could be separated into two chemotypes by multivariate analysis. The study of species exhibiting such intraspecific and intrasexual CHC variation will advance our understanding of the effects of CHC variability on both, desiccation resistance and intraspecific communication.

Immune Stimulation via Wounding Alters Chemical Profiles of Adult Tribolium castaneum

Group-living individuals experience immense risk of disease transmission and parasite infection. In social and in some non-social insects, disease control with immunomodulation arises not only via individual immune defenses, but also via infochemicals such as contact cues and (defensive) volatiles to mount a group-level immunity. However, little is known about whether activation of the immune system elicits changes in chemical phenotypes, which may mediate these responses. We here asked whether individual immune experience resulting from wounding or injection of heat-killed Bacillus thuringiensis (priming) leads to changes in the chemical profiles of female and male adult red flour beetles, Tribolium castaneum, which are non-social but gregarious. We analyzed insect extracts using GC-FID to study the chemical composition of (1) cuticular hydrocarbons (CHCs) as candidates for the transfer of immunity-related information between individuals via contact, and (2) stink gland secretions, with analysis of benzoquinones as main active compounds regulating 'external immunity'. Despite a pronounced sexual dimorphism in CHC profiles, wounding stimulation led to similar profile changes in males and females with increases in the proportion of methyl-branched alkanes compared to naïve beetles. While changes in the overall secretion profiles were less pronounced, absolute amounts of benzoquinones were transiently elevated in wounded compared to naïve females. Responses to priming were insignificant in CHCs and secretions. We suggest that changes in different infochemicals after wounding may mediate immune status signaling in the context of both internal and external immune responses in groups of this non-social insect, thus showing parallels to social immunity.

Mutagenesis of the odorant receptor co-receptor (Orco) reveals severe olfactory defects in the crop pest moth Helicoverpa armigera

BACKGROUND

Odorant receptors (ORs) as odorant-gated ion channels play a crucial role in insect olfaction. They are formed by a heteromultimeric complex of the odorant receptor co-receptor (Orco) and a ligand-selective Or. Other types of olfactory receptor proteins, such as ionotropic receptors (IRs) and some gustatory receptors (GRs), are also involved in the olfactory system of insects. Orco as an obligatory subunit of ORs is highly conserved, providing an opportunity to systematically evaluate OR-dependent olfactory responses.

RESULTS

Herein, we successfully established a homozygous mutant (Orco^-/-) of Helicoverpa armigera, a notorious crop pest, using the CRISPR/Cas9 gene editing technique. We then compared the olfactory response characteristics of wild type (WT) and Orco^-/- adults and larvae. Orco^-/- males were infertile, while Orco^-/- females were fertile. The lifespan of Orco^-/- females was longer than that of WT females. The expressions of most Ors, Irs, and other olfaction-related genes in adult antennae of Orco^-/- moths were not obviously affected, but some of them were up- or down-regulated. In addition, there was no change in the neuroanatomical phenotype of Orco^-/- moths at the level of the antennal lobe (including the macroglomerular complex region of the male). Using EAG and SSR techniques, we discovered that electrophysiological responses of Orco^-/- moths to sex pheromone components and many host plant odorants were absent. The upwind flight behaviors toward sex pheromones of Orco^-/- males were severely reduced in a wind tunnel experiment. The oviposition selectivity of Orco^-/- females to the host plant (green pepper) has completely disappeared, and the chemotaxis toward green pepper was also lost in Orco^-/- larvae.

CONCLUSIONS

Our study indicates that OR-mediated olfaction is essential for pheromone communication, oviposition selection, and larval chemotaxis of H. armigera, suggesting a strategy in which mate searching and host-seeking behaviors of moth pests could be disrupted by inhibiting or silencing Orco expression.

Low radiodensity μCT scans to reveal detailed morphology of the termite leg and its subgenual organ

Termites sense tiny substrate-borne vibrations through subgenual organs (SGOs) located within their legs' tibiae. Little is known about the SGOs' structure and physical properties. We applied high-resolution (voxel size 0.45 μm) micro-computed tomography (μCT) to Australian termites, Coptotermes lacteus and Nasutitermes exitiosus (Hill) to test two staining techniques. We compared the effectiveness of a single stain of Lugol's iodine solution (LS) to LS followed by Phosphotungstic acid (PTA) solutions (1% and 2%). We then present results of a soldier of Nasutitermes exitiosus combining μCT with LS + 2%PTS stains and scanning electron microscopy to exemplify the visualisation of their SGOs. The termite's SGO due to its approximately oval shape was shown to have a maximum diameter of 60 μm and a minimum of 48 μm, covering 60 ± 4% of the leg's cross-section and 90.4 ± 5% of the residual haemolymph channel. Additionally, the leg and residual haemolymph channel cross-sectional area decreased around the SGO by 33% and 73%, respectively. We hypothesise that this change in cross-sectional area amplifies the vibrations for the SGO. Since SGOs are directly connected to the cuticle, their mechanical properties and the geometric details identified here may enable new approaches to determine how termites sense micro-vibrations.

Rustling ants: Vibrational communication performed by two Camponotus species in Borneo

Interactions between ants and plants are classic examples of cooperation between individuals of different species. Usually, plants provide shelter or food for ants and in turn are defended against herbivores by their insect allies. To coordinate attacks, ants use multi-modal alarm signals consisting of vibrational and chemical components. This can also be observed in Borneo, where two Camponotus species inhabit the ocreas (diverging, tubular leaf sheaths) of the rattan palm Korthalsia robusta. When ants are disturbed, they beat or scratch mandibles and abdomens on the plant surface resulting in loud rustling sounds. To describe the characteristics of these signals, we recorded them with a Laser-Doppler-vibrometer in the field. Analyses of temporal patterns and dominant frequency revealed that the signals of the two species differ fundamentally. To assess transmission characteristics of the rattan palm, we conducted experiments under controlled lab-conditions. We show that the ocrea is an adequate structure for converting airborne sound into substrate vibrations, acting as a mediator between these two modalities. We hypothesize that the ants' vibratory signal has multiple functions, with the substrate-borne component used as an alarm signal for conspecifics, and the airborne component acting as vibro-acoustic aposematism against predators or herbivores to protect the host plant.

Species recognition limits mating between hybridizing ant species

Identifying mechanisms limiting hybridization is a central goal of speciation research. Here, we studied premating and postmating barriers to hybridization between two ant species, Formica selysi and Formica cinerea. These species hybridize in the Rhône valley in Switzerland, where they form a mosaic hybrid zone, with limited introgression from F. selysi into F. cinerea. There was no sign of temporal isolation between the two species in the production of queens and males. With choice experiments, we showed that queens and males strongly prefer to mate with conspecifics. Yet, we did not detect postmating barriers caused by genetic incompatibilities. Specifically, hybrids of all sexes and castes were found in the field and F1 hybrid workers did not show reduced viability compared to nonhybrid workers. To gain insights into the cues involved in species recognition, we analyzed the cuticular hydrocarbons (CHCs) of queens, males, and workers and staged dyadic encounters between workers. CHC profiles differed markedly between species, but were similar in F. cinerea and hybrids. Accordingly, workers also discriminated species, but they did not discriminate F. cinerea and hybrids. We discuss how the CHC-based recognition system of ants may facilitate the establishment of premating barriers to hybridization, independent of hybridization costs.

Evidence for a conserved queen-worker genetic toolkit across slave-making ants and their ant hosts

The ecological success of social Hymenoptera (ants, bees, wasps) depends on the division of labour between the queen and workers. Each caste exhibits highly specialised morphology, behaviour, and life-history traits, such as lifespan and fecundity. Despite strong defences against alien intruders, insect societies are vulnerable to social parasites, such as workerless inquilines or slave-making ants. Here, we investigate whether gene expression varies in parallel ways between lifestyles (slave-making versus host ants) across five independent origins of ant slavery in the "Formicoxenus-group" of the ant tribe Crematogastrini. As caste differences are often less pronounced in slave-making ants than in non-parasitic ants, we also compare caste-specific gene expression patterns between lifestyles. We demonstrate a substantial overlap in expression differences between queens and workers across taxa, irrespective of lifestyle. Caste affects the transcriptomes much more profoundly than lifestyle, as indicated by 37 times more genes being linked to caste than to lifestyle and by multiple caste-associated modules of co-expressed genes with strong connectivity. However, several genes and one gene module are linked to slave-making across the independent origins of this parasitic lifestyle, pointing to some evolutionary convergence. Finally, we do not find evidence for an interaction between caste and lifestyle, indicating that caste differences in gene expression remain consistent even when species switch to a parasitic lifestyle. Our findings strongly support the existence of a core set of genes whose expression is linked to the queen and worker caste in this ant taxon, as proposed by the "genetic toolkit" hypothesis.

Why do ants differ in acclimatory ability? Biophysical mechanisms behind cuticular hydrocarbon acclimation across species

Maintaining water balance is vital for terrestrial organisms. Insects protect themselves against desiccation via cuticular hydrocarbons (CHCs). CHC layers are complex mixtures of solid and liquid hydrocarbons, with a surprisingly diverse composition across species. This variation may translate to differential phase behaviour, and hence varying waterproofing capacity. This is especially relevant when temperatures change, which requires acclimatory CHC changes to maintain waterproofing. Nevertheless, the physical consequences of CHC variation are still little understood. We studied acclimatory responses and their consequences for CHC composition, phase behaviour, and drought survival in three congeneric ant species. Colony fragments were kept under cool, warm, and fluctuating temperature regimes. Lasius niger and platythorax, both of which are rich in methyl-branched alkanes, showed largely predictable acclimatory changes of the CHC profile. In both species, warm acclimation increased drought resistance. Warm acclimation increased the proportion of solid compounds in L. niger but not in L. platythorax. In both species, the CHC layer formed a liquid matrix of constantly low viscosity, which contained highly viscous and solid parts. This phase heterogeneity may be adaptive, increasing robustness to temperature fluctuations. In L. brunneus, which is rich in unsaturated hydrocarbons, acclimatory CHC changes were less predictable, and warm acclimation did not enhance drought survival. The CHC layer was more homogenous, but matrix viscosity changed with acclimation. We showed that ant species use different physical mechanisms to enhance waterproofing during acclimation. Hence, the ability to acclimate, and thus climatic niche breadth, may strongly depend on species-specific CHC profile.

Chemical cues of identity and reproductive status in Japanese macaques

Olfactory communication plays an important role in the regulation of socio-sexual interactions in mammals. There is growing evidence that both human and nonhuman primates rely on odors to inform their mating decisions. Nevertheless, studies of primate chemical ecology remain scarce due to the difficulty of obtaining and analyzing samples. We analyzed 67 urine samples from five captive female Japanese macaques (Macaca fuscata) and 30 vaginal swabs from three of these females using gas chromatography-mass spectrometry and examined the relationship between odor (compounds identified, richness, intensity, and diversity) and female identity as well as cycle phase. We found a total of 36 urine compounds of which we identified 31, and 68 vaginal compounds of which we identified 37. Our results suggest that urine and vaginal odor varied more between individuals than within cycle phases. However, we found that within a female cycle, urine samples from similar phases may cluster more than samples from different phases. Our results suggest that female odor may encode information about identity (vaginal and urine odor) and reproductive status (urine odor). The question of how conspecifics use female urine and vaginal odor remains open and could be tested using bioassays. Our results and their interpretation are constrained by our limited sample size and our study design. Nonetheless, our study provides insight into the potential signaling role of female odor in sexual communication in Japanese macaques and contributes to our understanding of how odors may influence mating strategies in primates.

Social Cues of Safety Can Override Differences in Threat Level

Animals in groups integrate social with directly gathered information about the environment to guide decisions regarding reproduction, foraging, and defence against predatory threats. In the context of predation, usage of social information has acute fitness benefits, aiding the detection of predators, the mounting of concerted defensive responses, or allowing the inference of safety, permitting other beneficial behaviors, such as foraging for food. We previously showed that Drosophila melanogaster exposed to an inescapable visual threat use freezing by surrounding flies as a cue of danger and movement resumption as a cue of safety. Moreover, group responses were primarily guided by the safety cues, resulting in a net social buffering effect, i.e., a graded decrease in freezing behavior with increasing group sizes, similar to other animals. Whether and how different threat levels affect the use of social cues to guide defense responses remains elusive. Here, we investigated this issue by exposing flies individually and in groups to two threat imminences using looms of different speeds. We showed that freezing responses are stronger to the faster looms regardless of social condition. However, social buffering was stronger for groups exposed to the fast looms, such that the increase in freezing caused by the higher threat was less prominent in flies tested in groups than those tested individually. Through artificial control of movement, we created groups composed of moving and freezing flies and by varying group composition, we titrated the motion cues that surrounding flies produce, which were held constant across threat levels. We found that the same level of safety motion cues had a bigger weight on the flies’ decisions when these were exposed to the higher threat, thus overriding differences in perceived threat levels. These findings shed light on the “safety in numbers” effect, revealing the modulation of the saliency of social safety cues across threat intensities, a possible mechanism to regulate costly defensive responses.

Genetic and genomic architecture of species-specific cuticular hydrocarbon variation in parasitoid wasps

Cuticular hydrocarbons (CHCs) serve two fundamental functions in insects: protection against desiccation and chemical signalling. How the interaction of genes shapes CHC profiles, which are essential for insect survival, adaptation and reproductive success, is still poorly understood. Here we investigate the genetic and genomic basis of CHC biosynthesis and variation in parasitoid wasps of the genus Nasonia. We mapped 91 quantitative trait loci (QTL) explaining the variation of a total of 43 CHCs in F₂ hybrid males from interspecific crosses between three Nasonia species. To identify candidate genes, we localized orthologues of CHC biosynthesis-related genes in the Nasonia genomes. We discovered multiple genomic regions where the location of QTL coincides with the location of CHC biosynthesis-related candidate genes. Most conspicuously, on a region close to the centromere of chromosome 1, multiple CHC biosynthesis-related candidate genes co-localize with several QTL explaining variation in methyl-branched alkanes. The genetic underpinnings behind this compound class are not well understood so far, despite their high potential for encoding chemical information as well as their prevalence in hymenopteran CHC profiles. Our study considerably extends our knowledge on the genetic architecture governing this important compound class, establishing a model for methyl-branched alkane genetics in the Hymenoptera in general.

Composition of a chemical signalling trait varies with phylogeny and precipitation across an Australian lizard radiation

The environment presents challenges to the transmission and detection of animal signalling systems, resulting in selective pressures that can drive signal divergence amongst populations in disparate environments. For chemical signals, climate is a potentially important selective force because factors such as temperature and moisture influence the persistence and detection of chemicals. We investigated an Australian lizard radiation (Heteronotia) to explore relationships between a sexually dimorphic chemical signalling trait (epidermal pore secretions) and two key climate variables: temperature and precipitation. We reconstructed the phylogeny of Heteronotia with exon capture phylogenomics, estimated phylogenetic signal in amongst-lineage chemical variation and assessed how chemical composition relates to temperature and precipitation using multivariate phylogenetic regressions. High estimates of phylogenetic signal indicate that the composition of epidermal pore secretions varies amongst lineages in a manner consistent with Brownian motion, although there are deviations to this, with stark divergences coinciding with two phylogenetic splits. Accounting for phylogenetic non-independence, we found that amongst-lineage chemical variation is associated with geographic variation in precipitation but not temperature. This contrasts somewhat with previous lizard studies, which have generally found an association between temperature and chemical composition. Our results suggest that geographic variation in precipitation can affect the evolution of chemical signalling traits, possibly influencing patterns of divergence amongst lineages and species.

Annotation and Analysis of 3902 Odorant Receptor Protein Sequences from 21 Insect Species Provide Insights into the Evolution of Odorant Receptor Gene Families in Solitary and Social Insects

The gene family of insect olfactory receptors (ORs) has expanded greatly over the course of evolution. ORs enable insects to detect volatile chemicals and therefore play an important role in social interactions, enemy and prey recognition, and foraging. The sequences of several thousand ORs are known, but their specific function or their ligands have only been identified for very few of them. To advance the functional characterization of ORs, we have assembled, curated, and aligned the sequences of 3902 ORs from 21 insect species, which we provide as an annotated online resource. Using functionally characterized proteins from the fly Drosophila melanogaster, the mosquito Anopheles gambiae and the ant Harpegnathos saltator, we identified amino acid positions that best predict response to ligands. We examined the conservation of these predicted relevant residues in all OR subfamilies; the results showed that the subfamilies that expanded strongly in social insects had a high degree of conservation in their binding sites. This suggests that the ORs of social insect families are typically finely tuned and exhibit sensitivity to very similar odorants. Our novel approach provides a powerful tool to exploit functional information from a limited number of genes to study the functional evolution of large gene families.