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Parental-care behaviours include mammalian lactation to provide milk for offspring. The discovery that adult ants harvest nutritious fluid from pupae and give larvae this fluid reveals social feeding that aids colony success. Moulting fluid from ant pupae is a food source that aids colony success. Close up of a nest of Ooceraea biroi clonal raider ants with workers, pupae, and young larvae

Studying food distribution in ant groups is essential for investigating social behavior, offering valuable insights into resource allocation, group dynamics, and environmental adaptation, thereby advancing ecological research. In this work, a highly sensitive and quantitative experimental tool was developed to visualize changes over time in food distribution within ant groups using positron-emitting radionuclides and a radiation imaging system. Food distribution observations within a 100-ant group allowed changes in an index of dispersion for food allocation to be quantified for 3 h. The method’s accuracy was confirmed by cross-checking with the results of a conventional quantification method using a gamma counter. Additionally, we successfully visualized food distribution in a 12-ant group and quantified the amount of food exchanged over a 30-min period. This method can be used to elucidate the mechanisms that control food distribution.

We report comprehensive evidence for obligatory thelytokous parthenogenesis in an ant Monomorium triviale . This species is characterized by distinct queen–worker dimorphism with strict reproductive division of labor: queens produce both workers and new queens without mating, whereas workers are completely sterile. We collected 333 nests of this species from 14 localities and three laboratory-reared populations in Japan. All wild queens dissected had no sperm in their spermathecae. Laboratory observation confirmed that virgin queens produced workers without mating. Furthermore, microsatellite genotyping showed identical heterozygous genotypes between mothers and their respective daughters, suggesting an extremely low probability of sexual reproduction. Microbial analysis detected no bacterial genera that are known to induce thelytokous parthenogenesis in Hymenoptera. Finally, the lack of variation in partial sequences of mitochondrial DNA among individuals sampled from across Japan suggests recent rapid spread or selective sweep. M . triviale would be a promising model system of superorganism-like adaptation through comparative analysis with well-studied sexual congeners, including the pharaoh ant M . pharaonis .

Females of social Hymenoptera only mate at the beginning of their adult lives and produce offspring until their death. In most ant species, queens live for over a decade, indicating that ant queens can store large numbers of spermatozoa throughout their long lives. To reveal the prolonged sperm storage mechanisms, we identified enriched genes in the sperm-storage organ (spermatheca) relative to those in body samples in Crematogaster osakensis queens using the RNA-sequencing method. The genes encoding antioxidant enzymes, proteases, and extracellular matrix-related genes, and novel genes that have no similar sequences in the public databases were identified. We also performed differential expression analyses between the virgin and mated spermathecae or between the spermathecae at 1-week and 1-year after mating, to identify genes altered by the mating status or by the sperm storage period, respectively. Gene Ontology enrichment analyses suggested that antioxidant function is enhanced in the spermatheca at 1-week after mating compared with the virgin spermatheca and the spermatheca at 1-year after mating. In situ hybridization analyses of 128 selected contigs revealed that 12 contigs were particular to the spermatheca. These genes have never been reported in the reproductive organs of insect females, suggesting specialized roles in ant spermatheca.

Understanding the mechanisms underlying the successful invasion of the guppy, Poecilia reticulata , a globally invasive species, is important in the field of invasion biology. The body color pattern of male guppies is known to influence predation risk; however, the relationship between body color pattern and local predator guilds has been addressed in only a few studies. To investigate this relationship, we analyzed 32 water samples and 305 male guppies from eight introduced populations on the main island of Okinawa, Japan. The environmental DNA metabarcoding analysis of teleosts from the waters identified six potential guppy predator families, Anguillidae, Eleotridae, Gobiidae, Cichlidae, Mugilidae, and Cyprinidae; however, there was no detection of Characiformes, which are one of the major predators of guppies in their original habitat. Using imaging analysis of color spot areas of male guppies, we found that 16 of 18 potential predator × color combinations exhibited a statistically significant association between body color and the presence of predator families. For example, a negative association between orange spots and Anguillidae, and a positive association between blue-green spots and Cichlidae. These results suggest that the guppy in Okinawa was ecologically released from a major predator in its native habitat and adapted to the new environment through color pattern changes.

Social insects demonstrate adaptive behaviour for a given colony size. Remarkably, most species do this even without visual information in a dark environment. However, how they achieve this is yet unknown. Based on individual trait expression, an agent-based simulation was used to identify an explicit mechanism for understanding colony size dependent behaviour. Through repeated physical contact between the queen and individual workers, individual colony members monitor the physiological states of others, reflecting such contact information in their physiology and behaviour. Feedback between the sensing of physiological states and the corresponding behaviour patterns leads to self-organisation with colonies shifting according to their size. We showed (1) the queen can exhibit adaptive behaviour patterns for the increase in colony size while density per space remains unchanged, and (2) such physical constraints can underlie the adaptive switching of colony stages from successful patrol behaviour to unsuccessful patrol behaviour, which leads to constant ovary development (production of reproductive castes). The feedback loops embedded in the queen between the perception of internal states of the workers and behavioural patterns can explain the adaptive behaviour as a function of colony size.

Partner discrimination is crucial in mutualistic interactions between organisms to counteract cheating by the partner. Trophobiosis between ants and aphids is a model system of such mutualistic interaction. To establish and maintain the mutualistic association, ants need to correctly discriminate mutualistic aphids. However, the mechanism by which ants recognize aphids as their partners is poorly understood, despite its ecological and evolutionary importance. Here, we show for the first time the evidence that interaction with nest-mates that have tended aphids (Aphis craccivora) allows ants (Tetramorium tsushimae) to learn to recognize the aphid species as their partner. When ants had previously tended aphids, they moderated their aggressiveness towards aphids. More importantly, ants that had interacted with aphid-experienced nest-mates also reduced their aggressiveness towards aphids, even though they had never directly experienced them, indicating that aphid information was transmitted from aphid-experienced ants to inexperienced ants. Furthermore, inhibition of mouth-to-mouth contact (trophallaxis) from aphid-experienced ants to inexperienced ants by providing the inexperienced ants with artificial honeydew solution caused the inexperienced ants to become aggressive towards aphids. These results, with further supporting data, strongly suggest that ants transfer information on their mutualists during trophallactic interactions.

Cooperation in biological, social, and economic groups is underpinned by public goods that are generated by group members at some personal cost. Theory predicts that public goods will be exploited by cheaters who benefit from the goods by not paying for them, thereby leading to the collapse of cooperation. This situation, described as the “public goods dilemma” in game theory, makes the ubiquity of cooperation a major evolutionary puzzle. Despite this generalization, the demonstration of genetic background and fitness effects of the public goods dilemma has been limited to interactions between viruses and between cells, and thus its relevance at higher levels of organismal complexity is still largely unexplored. Here we provide experimental evidence for the public goods dilemma in a social insect, the ant Pristomyrmex punctatus . In this species, all workers are involved in both asexual reproduction and cooperative tasks. Genetic cheaters infiltrate field colonies, reproducing more than the workers but shunning cooperative tasks. In laboratory experiments, cheaters outcompeted coexisting workers in both survival and reproduction, although a group composed only of cheaters failed to produce offspring. The operations of the public goods dilemma in P. punctatus showed a remarkable convergence with those in microbial societies, not only in fitness consequences but also in behavioral mechanisms. Our study reinforces the evolutionary impact of cheaters on diverse cooperative systems in the laboratory and in the field.

Ant colonies have either a single nest (monodomy) or multiple nests (polydomy). A challenge is to explain their adaptive significance, specifying costs and benefits of each colony type. An explanation for ant polydomy is adaptation to spatially heterogeneous environments. With polydomy a colony can exchange complementary nutrition among nests within the entire colony occupying a wide territory. We tested this resource redistribution hypothesis using two closely related species, i.e. the polydomous ant Pheidole megacephala and the monodomous ant Pheidole noda. We put each colony in an artificially polydomous setting with two nests connected by tubes. We provided liquid food lacking protein to one nest and that lacking carbohydrates to the other nest. P. megacephala almost totally failed to produce brood when the connecting tubes were clipped, whereas it improved reproductive performance when the tubes were open. In marked contrast, P. noda managed to maintain high performance for a long period even when only nutritionally biased food was provided, most likely by relying on stored provisions that compensated for the missing nutrients. Based on these data, we propose the hypothesis that ant polydomy is an open economic strategy to counter heterogeneity in resource distribution ‘spatially’ by trading between nests and extending the resource searching area, whereas monodomy may be a closed economic strategy to cope with resource heterogeneity ‘temporally’ by withstanding food-depressed periods with stored nutrition and by efficient utilization of frugal diets. More empirical data in other ant taxa are necessary to test generality of this idea.

Early-stage control of invasive ants provides an opportunity to suppress establishment while conserving existing biodiversity. We developed and tested a selective control strategy targeting the Browsing ant Lepisiota frauenfeldi, an emerging omnivorous, polygynous, and polydomous invader, during its initial establishment in an urban area of Okinawa Island, Japan. Because the local ant community was still present when the invasion was detected, the trial aimed at reducing the competitive advantage of the target species while preserving biotic resistance from resident species. We hypothesized that weakening L. frauenfeldi through selective chemical treatment would allow existing species to occupy its vacant niches, thereby accelerating eradication. Species-specific baits were formulated using a growth regulator with protein- and carbohydrate-based substrates. Baits were placed near nest entrances identified through monthly surveys over an area of approximately 1.6 hectares. Ant community dynamics were monitored for 44 months using hand-collection and sticky-trap surveys. The invasive ant showed a strong negative response to treatment, with an estimated 92% reduction in occurrence probability, ultimately disappearing from the treated area. Several non-target ant species increased in frequency, consistent with expectation of the niche reoccupation, while most other species remained stable, indicating minimal impact on the broader community. Compared to conventional methods, this approach used drastically less chemical while achieving high efficacy. Implementation through cross-organizational collaboration enabled parallel treatment in adjacent restricted areas and contributed to the program's success. These results highlight the practical and ecological value of nest-targeted, community-collaborative selective baiting as a strategy for managing omnivorous invasive ants during early establishment.