A larval ‘princess pheromone’ identifies future ant queens based on their juvenile hormone content

Evolution: How sweat bees gained and lost eusociality

Eusocial insects divide labor between reproductive and non-reproductive individuals. The molecular mechanisms underlying the evolution of these castes have remained mysterious. A comparative genomic study of sweat bees points to a familiar factor as a regulator of behavioral specialization: juvenile hormone.

Queens control caste allocation in the ant Cardiocondyla obscurior

Social insect queens and workers can engage in conflict over reproductive allocation when they have different fitness optima. Here, we show that queens have control over queen-worker caste allocation in the ant Cardiocondyla obscurior, a species in which workers lack reproductive organs. We describe crystalline deposits that distinguish castes from the egg stage onwards, providing the first report of a discrete trait that can be used to identify ant caste throughout pre-imaginal development. The comparison of queen and worker-destined eggs and larvae revealed size and weight differences in late development, but no discernible differences in traits that may be used in social interactions, including hair morphology and cuticular odours. In line with a lack of caste-specific traits, adult workers treated developing queens and workers indiscriminately. Together with previous studies demonstrating queen control over sex allocation, these results show that queens control reproductive allocation in C. obscurior and suggest that the fitness interests of colony members are aligned to optimize resource allocation in this ant.

The Scent of Ant Brood: Caste Differences in Surface Hydrocarbons of Formica exsecta Pupae

Chemical communication is common across all organisms. Insects in particular use predominantly chemical stimuli in assessing their environment and recognizing their social counterparts. One of the chemical stimuli used for recognition in social insects, such as ants, is the suite of long-chain, cuticular hydrocarbons. In addition to providing waterproofing, these surface hydrocarbons serve as a signature mixture, which ants can perceive, and use to distinguish between strangers and colony mates, and to determine caste, sex, and reproductive status of another individual. They can be both environmentally and endogenously acquired. The surface chemistry of adult workers has been studied extensively in ants, yet the pupal stage has rarely been considered. Here we characterized the surface chemistry of pupae of Formica exsecta, and examine differences among sexes, castes (reproductive vs. worker), and types of sample (developing individual vs. cocoon envelope). We found quantitative and qualitative differences among both castes and types of sample, but male and female reproductives did not differ in their surface chemistry. We also found that the pupal surface chemistry was more complex than that of adult workers in this species. These results improve our understanding of the information on which ants base recognition, and highlights the diversity of surface chemistry in social insects across developmental stages.

Reproduction and signals regulating worker policing under identical hormonal control in social wasps

In social Hymenoptera, fertility and fertility signalling are often under identical hormonal control, and it has been suggested that such hormonal pleiotropies can help to maintain signal honesty. In the common wasp Vespula vulgaris, for example, fertile queens have much higher juvenile hormone (JH) titers than workers, and JH also controls the production of chemical fertility cues present on the females’ cuticle. To regulate reproductive division of labour, queens use these fertility cues in two distinct ways: as queen pheromones that directly suppress the workers’ reproduction as well as to mark queen eggs and enable the workers to recognize and police eggs laid by other workers. Here, we investigated the hormonal pleiotropy hypothesis by testing if experimental treatment with the JH analogue methoprene could enable the workers to lay eggs that evade policing. In support of this hypothesis, we find that methoprene-treated workers laid more eggs, and that the chemical profiles of their eggs were more queen-like, thereby causing fewer of their eggs to be policed compared to in the control. Overall, our results identify JH as a key regulator of both reproduction and the production of egg marking pheromones that mediate policing behaviour in eusocial wasps.

Biological aspects of Myopopone castanea on it's prey Oryctes rhinoceros larvae

Ants are social insects with some significant roles in the ecosystem, including acting as predators for various insect pests. Myopopone castanea ants is a predatorfor the larvae of Oryctes rhinoceros pest. The existence of a similar niche of life between M. castanea ants and O. rhinoceros larvae opens an excellent opportunity to utilize these ants as biological agents. The research was conducted to study some aspects biology of M. castanea so that later it can be applied to mass rearing of natural enemies in the laboratory. The study was conducted by maintaining 50 eggs of M. castanea ant. Then, the eggs placed on two pieces of decayed palm oil stem together with twenty individual worker ants and ten individual end instar larvae. It needs five replications for the experiment. The results showed that egg stadia length was 13.8 days. It found five instars within M. castanea ant larvae with varying lengths of each stage. It takes 17.2 days for worker ant pupae to go through stadia pupa and 17.9 days for female ant pupae. The survival rate of M. castanea ant life from eggs until imago is 56.4%, which means that from several groups of eggs laid by queen ants, only about half have succeeded in becoming ant imago.

Transcriptomic basis and evolution of the ant nurse-larval social interactome

Development is often strongly regulated by interactions among close relatives, but the underlying molecular mechanisms are largely unknown. In eusocial insects, interactions between caregiving worker nurses and larvae regulate larval development and resultant adult phenotypes. Here, we begin to characterize the social interactome regulating ant larval development by collecting and sequencing the transcriptomes of interacting nurses and larvae across time. We find that the majority of nurse and larval transcriptomes exhibit parallel expression dynamics across larval development. We leverage this widespread nurse-larva gene co-expression to infer putative social gene regulatory networks acting between nurses and larvae. Genes with the strongest inferred social effects tend to be peripheral elements of within-tissue regulatory networks and are often known to encode secreted proteins. This includes interesting candidates such as the nurse-expressed giant-lens, which may influence larval epidermal growth factor signaling, a pathway known to influence various aspects of insect development. Finally, we find that genes with the strongest signatures of social regulation tend to experience relaxed selective constraint and are evolutionarily young. Overall, our study provides a first glimpse into the molecular and evolutionary features of the social mechanisms that regulate all aspects of social life.

Transcriptomic basis and evolution of the ant nurse-larval social interactome

Development is often strongly regulated by interactions among close relatives, but the underlying molecular mechanisms are largely unknown. In eusocial insects, interactions between caregiving worker nurses and larvae regulate larval development and resultant adult phenotypes. Here, we begin to characterize the social interactome regulating ant larval development by collecting and sequencing the transcriptomes of interacting nurses and larvae across time. We find that the majority of nurse and larval transcriptomes exhibit parallel expression dynamics across larval development. We leverage this widespread nurse-larva gene co-expression to infer putative social gene regulatory networks acting between nurses and larvae. Genes with the strongest inferred social effects tend to be peripheral elements of within-tissue regulatory networks and are often known to encode secreted proteins. This includes interesting candidates such as the nurse-expressed giant-lens, which may influence larval epidermal growth factor signaling, a pathway known to influence various aspects of insect development. Finally, we find that genes with the strongest signatures of social regulation tend to experience relaxed selective constraint and are evolutionarily young. Overall, our study provides a first glimpse into the molecular and evolutionary features of the social mechanisms that regulate all aspects of social life.

The role of juvenile hormone in regulating reproductive physiology and dominance in Dinoponera quadriceps ants

Unequal reproductive output among members of the same sex (reproductive skew) is a common phenomenon in a wide range of communally breeding animals. In such species, reproductive dominance is often acquired during antagonistic interactions between group members that establish a reproductive hierarchy in which only a few individuals reproduce. Rank-specific syndromes of behavioural and physiological traits characterize such hierarchies, but how antagonistic behavioural interactions translate into stable rank-specific syndromes remains poorly understood. The pleiotropic nature of hormones makes them prime candidates for generating such syndromes as they physiologically integrate environmental (social) information, and often affect reproduction and behaviour simultaneously. Juvenile hormone (JH) is one of several hormones that occupy such a central regulatory role in insects and has been suggested to regulate reproductive hierarchies in a wide range of social insects including ants. Here we use experimental manipulation to investigate the effect of JH levels on reproductive physiology and social dominance in high-ranked workers of the eusocial ant Dinoponera quadriceps, a species that has secondarily reverted to queenless, simple societies. We show that JH regulated reproductive physiology, with ants in which JH levels were experimentally elevated having more regressed ovaries. In contrast, we found no evidence of JH levels affecting dominance in social interactions. This could indicate that JH and ovary development are decoupled from dominance in this species, however only high-ranked workers were investigated. The results therefore confirm that the regulatory role of JH in reproductive physiology in this ant species is in keeping with its highly eusocial ancestors rather than its secondary reversion to simple societies, but more investigation is needed to disentangle the relationships between hormones, behaviour and hierarchies.

Social regulation of a rudimentary organ generates complex worker-caste systems in ants

The origin of complex worker-caste systems in ants perplexed Darwin1 and has remained an enduring problem for evolutionary and developmental biology2-6. Ants originated approximately 150 million years ago, and produce colonies with winged queen and male castes as well as a wingless worker caste7. In the hyperdiverse genus Pheidole, the wingless worker caste has evolved into two morphologically distinct subcastes-small-headed minor workers and large-headed soldiers8. The wings of queens and males develop from populations of cells in larvae that are called wing imaginal discs7. Although minor workers and soldiers are wingless, vestiges or rudiments of wing imaginal discs appear transiently during soldier development7,9-11. Such rudimentary traits are phylogenetically widespread and are primarily used as evidence of common descent, yet their functional importance remains equivocal1,12-14. Here we show that the growth of rudimentary wing discs is necessary for regulating allometry-disproportionate scaling-between head and body size to generate large-headed soldiers in the genus Pheidole. We also show that Pheidole colonies have evolved the capacity to socially regulate the growth of rudimentary wing discs to control worker subcaste determination, which allows these colonies to maintain the ratio of minor workers to soldiers. Finally, we provide comparative and experimental evidence that suggests that rudimentary wing discs have facilitated the parallel evolution of complex worker-caste systems across the ants. More generally, rudimentary organs may unexpectedly acquire novel regulatory functions during development to facilitate adaptive evolution.

Queen Control or Queen Signal in Ants: What Remains of the Controversy 25 Years After Keller and Nonacs' Seminal Paper?

Ant queen pheromones (QPs) have long been known to affect colony functioning. In many species, QPs affect important reproductive functions such as diploid larvae sexualization and egg-laying by workers, unmated queens (gynes), or other queens. Until the 1990s, these effects were generally viewed to be the result of queen manipulation through the use of coercive or dishonest signals. However, in their seminal 1993 paper, Keller and Nonacs challenged this idea, suggesting that QPs had evolved as honest signals that informed workers and other colony members of the queen's presence and reproductive state. This paper has greatly influenced the study of ant QPs and inspired numerous attempts to identify fertility-related compounds and test their physiological and behavioral effects. In the present article, we review the literature on ant QPs in various contexts and pay special attention to the role of cuticular hydrocarbons (CHCs). Although the controversy generated by Keller and Nonacs' (Anim Behav 45:787-794, 1993) paper is currently less intensively debated, there is still no clear evidence which allows the rejection of the queen control hypothesis in favor of the queen signal hypothesis. We argue that important questions remain regarding the mode of action of QPs, and their targets which may help understanding their evolution.

Identification of a queen and king recognition pheromone in the subterranean termite Reticulitermes flavipes

Chemical communication is fundamental to success in social insect colonies. Species-, colony-, and caste-specific blends of cuticular hydrocarbons (CHCs) and other chemicals have been well documented as pheromones, mediating important behavioral and physiological aspects of social insects. More specifically, royal pheromones used by queens (and kings in termites) enable workers to recognize and care for these vital individuals and maintain the reproductive division of labor. In termites, however, no royal-recognition pheromones have been identified to date. In the current study, solvent extracts of the subterranean termite Reticulitermes flavipes were analyzed to assess differences in cuticular compounds among castes. We identified a royal-specific hydrocarbon-heneicosane-and several previously unreported and highly royal enriched long-chain alkanes. When applied to glass dummies, heneicosane elicited worker behavioral responses identical to those elicited by live termite queens, including increased vibratory shaking and antennation. Further, the behavioral effects of heneicosane were amplified when presented with nestmate termite workers' cuticular extracts, underscoring the importance of chemical context in termite royal recognition. Thus, heneicosane is a royal-recognition pheromone that is active in both queens and kings of R. flavipes The use of heneicosane as a queen and king recognition pheromone by termites suggests that CHCs evolved as royal pheromones ∼150 million years ago, ∼50 million years before their first use as queen-recognition pheromones in social Hymenoptera. We therefore infer that termites and social Hymenoptera convergently evolved the use of these ubiquitous compounds in royal recognition.