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Termites are eusocial insects with functionally specialized workers and soldiers, both sharing the same genotype. Additionally, lower termites host flagellates in their hindguts that assist in wood digestion. However, worker-biased and soldier-biased gene expression patterns of the host–flagellate symbiotic system remain underexplored in most taxonomic groups. In this study, we sequenced high-depth transcriptomes from the workers and soldiers of a lower termite, Neotermes binovatus (Kalotermitidae), to investigate the differentially expressed termite transcripts, flagellate transcript abundance, and co-expression patterns of the host–flagellate transcript pairs in both castes. The worker-biased transcripts were enriched in functions related to cuticle development, nervous system regulation, pheromone biosynthesis, and metabolism, whereas the soldier-biased transcripts were predominantly involved in muscle development and kinesis, body morphogenesis, protein modification, and aggression. Flagellate transcripts from the orders Cristamonadida, Trichomonadida, Tritrichomonadida, and Oxymonadida were identified in both workers and soldiers, with the abundance of most flagellate transcripts tending to be higher in workers than in soldiers. Furthermore, we observed a much larger number of strong co-expression correlations between the termite and flagellate transcripts in workers than in soldiers, suggesting the possibility that soldiers depend more on food processed by worker holobionts than on their own symbiotic system. This research provides insights into the functional specialization of the host–flagellate symbiotic system in the worker and soldier castes of termites, supporting the workers’ roles in nest maintenance, preliminary food processing, and communication, while emphasizing the defensive role of soldiers. Additionally, it offers new perspectives on the potential termite-flagellate interactions and underscores the need for whole-genome data of termite flagellates in further studies.

Ants display a diversity of social structures reflected by differences in caste, nest, and colony organization. Previous research has shown that highly eusocial insects (Hymenoptera) exhibit genome‐wide signatures of relaxed selection due to their smaller effective population sizes. However, it is unknown how the colony structure itself may shape the evolution of eusocial species through its effects on the worker caste. Worker ants are typically sterile or produce only male offspring, so traits affecting their behavior evolve mainly through kin selection. Kin selection is predicted to be strongest when relatedness within the colony is high, as in species with a single queen per colony (monogyne). In these cases, the reproductive individuals who are the recipients of worker helping behavior are more likely to carry the same allele for that behavior, with probability proportional to relatedness between worker and reproductive. In contrast, in species with multiple queens and lower relatedness, like weakly or highly polygyne ants, there is a higher chance that altruistic behavior benefits non‐relatives. These colony structures are predicted to weaken kin selection, leading to more relaxed selection on worker‐biased genes. We find some evidence in highly polygyne species that genes with worker‐biased expression experience more relaxed selection compared to queen‐biased or non‐differentially expressed genes. However, this pattern does not appear to hold consistently across species with lower or more variable queen numbers, where the degree of relaxed selection in worker genes shows no clear association with average queen number per nest. This may point to possible compensatory mechanisms present in these contexts to counteract relaxed selection in workers or that these predicted patterns are too subtle to be detected with current methods, highlighting areas of future study.

Korea’s unique climate and agricultural environment suggest that the gut microbiome of honey bees may possess distinctive compositions influenced by regional factors. With the decline in honey bee populations and rising health challenges, understanding the role of gut microbiomes is essential for enhancing honey bee health and their resilience to environmental stressors. To explore caste-specific gut microbiota and identify microbial signatures associated with honey bee health, this study examined the gut microbial composition of worker bees, queen bees, and drones of using 16S rRNA gene amplicon sequencing. Analysis of beta diversity and species richness demonstrated significant differences between worker bees and both drones and queens, with no significant differences identified between drones and queens. Notably, dominated all groups, comprising 98.6% of the drones, 95.4% of the queens, and 68.3% of the workers. Additionally, was prominent in queens (4%), whereas (23%) and (4.7%) were notably enriched in workers. Drones and queens exhibited similar gut microbiome profiles, while workers displayed distinctly different compositions. These findings underscore the variation in gut microbiota composition and potential functional roles across honey bee castes. Such microbial distinctions may reflect caste-specific roles and physiological demands within the colony. Future research should investigate the physiological roles of gut microbiota and their contributions to environmental resilience, paving the way for microbiome-based strategies to promote honey bee health. This study lays a crucial scientific foundation for conserving the honey bee ecosystem and promoting sustainable agriculture.

When we get a cold and then stay home from work, we are not only taking care of ourselves but also protecting others. Such changes in behavior after infection are predicted in social animals but are difficult to quantify. Stroeymeyt et al. looked for such changes in the black garden ant and found that infected workers did alter their behavior—and healthy workers altered their behavior toward the sick. The changed behavior was especially valuable for protecting the most important and vulnerable members of the colony. Science , this issue p. 941 Sick black garden ants modify their behavior to protect the colony. Animal social networks are shaped by multiple selection pressures, including the need to ensure efficient communication and functioning while simultaneously limiting disease transmission. Social animals could potentially further reduce epidemic risk by altering their social networks in the presence of pathogens, yet there is currently no evidence for such pathogen-triggered responses. We tested this hypothesis experimentally in the ant Lasius niger using a combination of automated tracking, controlled pathogen exposure, transmission quantification, and temporally explicit simulations. Pathogen exposure induced behavioral changes in both exposed ants and their nestmates, which helped contain the disease by reinforcing key transmission-inhibitory properties of the colony’s contact network. This suggests that social network plasticity in response to pathogens is an effective strategy for mitigating the effects of disease in social groups.

An arboreal ant species by nature, the Asian weaver ant Oecophylla smaragdina F., (Hymenoptera: Formicidae) colony’s social structure composition was investigated in depth. Brood and barrack nests were collected from the African oil palm ( Elaeis guineensis ) canopies and Limau kasturi ( Citrus microcarpa ) orchards, and dissected. All caste’s morphological traits were examined stereo-microscopically. The workers’ width and length measurements of the separately dissected head, thorax, frontal view, abdomen, and body full side view sizes were recorded. All colonies comprise a founding queen laying thousands of eggs stored in a protective yellowish, unknown sticky substance (shining reflection), with reproductive winged green and newly emerged yellow queens, adult drone males, and wingless workers along their immature pupae and larvae arranged in woven, solid silken chambers (brood nests exclusively). Besides the traditionally known caste of minor and major workers, five polymorphic individuals comprising two unidentified novel sub-castes of intermediate workers and one sub-caste of major workers were described. The full body and abdomen lengths are proposed as dominant predicting factors differentiating among the five sub-castes. The discovery of a multimodal size frequency distribution model contrasts with the classical archetypical bimodal systems in ants. Intermediate workers foraging outside the nest revealed reconnaissance autonomy and aggressive behaviors that aided larger workers in securing the territorial perimeter. Bigger workers occupied the first defensive layers of the colony’s territorial frontier, while the intermediate workers maintained their stance at a closer nest distance. Major workers systematically acted as leaders-supervisors by removing individuals of smaller size during overheating exposure. Due to their short lifespan and segregated nests, it is difficult to collect adult males in wide plantations. A stable and average mature three-year-old colony produces several reproductive individuals monthly. The mean number of emerging queens is higher in older colonies (scarcity of males) and lower for younger colonies (queens-males averages are correlated). The queen production increases with higher rainfall and relative humidity. This study identified three novel worker sub-castes: one major intermediate, two intermediate in size. These findings contribute to a better understanding of the overall worker’s functional activity. The Asian weaver ant demonstrates adaptive measures in response to challenging abiotic factors (temperature), defying classical labor division rules.

When honey bee colonies collapse from high infestations of Varroa mites, neighboring colonies often experience surges in their mite populations. Collapsing colonies, often called \"mite bombs\", seem to pass their mites to neighboring colonies. This can happen by mite-infested workers from the collapsing colonies drifting into the neighboring colonies, or by mite-free workers from the neighboring colonies robbing out the collapsing colonies, or both. To study inter-colony mite transmission, we positioned six nearly mite-free colonies of black-colored bees around a cluster of three mite-laden colonies of yellow-colored bees. We then monitored the movement of bees between the black-bee and yellow-bee colonies before, during, and after mite-induced collapse of the yellow-bee colonies. Throughout the experiment, we monitored each colony's mite level. We found that large numbers of mites spread to the black-bee colonies (in both nearby and distant hives) when the yellow-bee colonies collapsed from high mite infestations and became targets of robbing by the black-bee colonies. We conclude that \"robber lures\" is a better term than \"mite bombs\" for describing colonies that are succumbing to high mite loads and are exuding mites to neighboring colonies.

The influence of gene expression on female caste determination in social Hymenoptera is one of the best-characterized examples of developmental polyphenism. We used mRNA-seq to profile differentially expressed genes (DEGs) between workers and queens at four development stages (early larvae: 1-day-old larvae; mid larvae: 5-day-old larvae; late larvae: 9-day-old larvae; and 7-day-old adult bee) of Bombus terrestris. When DEGs of different female castes were compared, it was found that there were more DEGs at the mid larval and adult stages than at other stages. Caste differentiation may be linked to candidate genes such as Vitellogenin, Kr-h1, Dnmt3, Hexamerin, Yellow, and Chymotrypsin-2. Additionally, the gene expression profiles were observed differently among the four development stages. Comparing one stage to the next showed that, more number of DEGs were found in queens than workers. In the investigation of how gene expression affects larval caste determination, WGCNA showed that five modules were closely associated with larval caste determination. The functions of genes were mainly enriched in energy metabolism and energy production within mitochondria, suggesting that the energy requirements during the larval development process varied between caste determination. The current study sheds light on the patterns of gene expression in the female caste of Bombus terrestris, which will be useful for future research on polyphenism through differential gene expressions.

The origin of complex worker-caste systems in ants perplexed Darwin 1 and has remained an enduring problem for evolutionary and developmental biology 2 – 6 . Ants originated approximately 150 million years ago, and produce colonies with winged queen and male castes as well as a wingless worker caste 7 . In the hyperdiverse genus Pheidole , the wingless worker caste has evolved into two morphologically distinct subcastes—small-headed minor workers and large-headed soldiers 8 . The wings of queens and males develop from populations of cells in larvae that are called wing imaginal discs 7 . Although minor workers and soldiers are wingless, vestiges or rudiments of wing imaginal discs appear transiently during soldier development 7 , 9 – 11 . Such rudimentary traits are phylogenetically widespread and are primarily used as evidence of common descent, yet their functional importance remains equivocal 1 , 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. In the ant genus Pheidole the growth of rudimentary wing discs—which influence developmental allometry to produce castes with distinct morphologies—is socially regulated to determine the worker-to-soldier ratio in Pheidole colonies.

Highly social insects are characterized by caste dimorphism, with distinct size differences of reproductive organs between fertile queens and the more or less sterile workers. An abundance of nutrition or instruction via diet-specific compounds has been proposed as explanations for the nutrition-driven queen and worker polyphenism. Here, we further explored these models in the honeybee (Apis mellifera) using worker nutrition rearing and a novel mutational screening approach using the clustered regularly interspaced short palindromic repeats/CRISPR-associated protein 9 (CRISPR/Cas9) method. The worker nutrition-driven size reduction of reproductive organs was restricted to the female sex, suggesting input from the sex determination pathway. Genetic screens on the sex determination genes in genetic females for size polyphenism revealed that doublesex (dsx) mutants display size-reduced reproductive organs irrespective of the sexual morphology of the organ tissue. In contrast, feminizer (fem) mutants lost the response to worker nutrition-driven size control. The first morphological worker mutants in honeybees demonstrate that the response to nutrition relies on a genetic program that is switched \"ON\" by the fem gene. Thus, the genetic instruction provided by the fem gene provides an entry point to genetically dissect the underlying processes that implement the size polyphenism.

Vitellogenin has been proposed to regulate division of labor and social organization in social insects. The red imported fire ant ( Solenopsis invicta ) harbors four distinct, adjacent vitellogenin genes (Vg1, Vg2, Vg3, and Vg4). Contrary to honey bees that have a single Vg ortholog as well as potentially fertile nurses, and to other ant species that lay trophic eggs, S. invicta workers completely lack ovaries or the ability to lay eggs. This provides a unique model to investigate whether Vg duplication in S. invicta was followed by subfunctionalization to acquire non-reproductive functions and whether Vg was co-opted to regulate behavior within the worker caste. To investigate these questions, we compared the expression patterns of S. invicta Vg genes among workers from different morphological subcastes or performing different tasks. RT-qPCRs revealed higher relative expression of Vg1 in major workers compared to both medium and minor workers, and of Vg2 in major workers when compared to minor workers. Relative expression of Vg1 was also higher in carbohydrate foragers when compared to nurses and protein foragers. By contrast, the level of expression of Vg2, Vg3, and Vg4 were not significantly different among the workers performing the specific tasks. Additionally, we analyzed the relationship between the expression of the Vg genes and S-hydroprene, a juvenile hormone analog. No changes in Vg expression were recorded in workers 12 h after application of the analog. Our results suggest that in S. invicta the Vg gene underwent subfunctionalization after duplication to new functions based on the expression bias observed in these data. This may suggest an alternative and still unknown function for Vg in the workers that needs to be investigated further.