Insectes Sociaux最新文献

Among eusocial insects, ants show the most advanced morphological division of labor with large winged queens, smaller wingless workers, and phenotypically intermediate castes. These intermediate castes may have evolved from the selection of developmental errors called intercastes. Intercastes are unusual phenotypes that show uncoordinated expression of worker and queen traits. These rare specimens provide remarkable insights into the advanced morphological evolution of the division of labor unique to ants. While they have been reported in several genera of the subfamily Myrmicinae, a single recent study described intercastes in the genus Aphaenogaster (210 spp). Here, we provide the first record of intercastes in an Asian species, Aphaenogaster rugulosa, endemic to the Japanese island of Yonaguni-jima. Using allometric measurements, scanning electron microscopy and dissections, we describe the trait combination of seven intercastes and compare it to worker and queen phenotypes. We discuss the modular origin of these rare phenotypes and elaborate on the potential role of intercastes in ant evolution.

When we think of social insects, earwigs rarely come to mind. This is perhaps not surprising, as the term ‘social insect’ has often been used in the literature to refer exclusively to ‘eusocial insects’, i.e. ants, termites and certain bees and wasps. However, earwigs show many aspects of social life. Social interactions in earwigs can occur in groups of up to several hundred individuals, with mothers providing extensive forms of care for their eggs and juveniles, and adults and juveniles showing cooperative behaviour with group members of the same and different ages. In this review, we discuss how research on the European earwig (by far the most studied dermapteran species in terms of its social life) can improve our general understanding of social evolution in insects. After outlining (1) its life cycle and (2) its multiple forms of sociality, we explain how this species advances our knowledge of (3) the interplay between social conflict and cooperation in maintaining facultative social life, (4) the role of pathogens and symbionts in the transition between solitary and social life, (5) the impact of anthropogenic change on social evolution, and (6) the chemical, hormonal and genetic regulation of facultative social behaviour. Overall, this review highlights that the study of social species such as the European earwig can provide unique insights into our general understanding of social evolution and the early evolutionary transitions from solitary to group living.

One of the few imperiled ant species in North America is the Comanche Harvester Ant, Pogonomyrmex comanche. Despite its status, little is known about its natural history throughout its range in the western Gulf Coastal Plain of North America. This study presents a regional phylogeographic analysis of P. comanche across sites in its natural range as a first step to learning more about this species. By using COI genotyping, we discovered that the center of genetic diversity is found in central Texas, which is typical for many species that found refugia in the southern North America during Pleistocene glaciations. Although diversity was slightly lower in northern populations, there was no evidence of recent population expansion into northern latitudes. Rather, some deviations from neutrality were consistent with population contraction in the northern regions (Arkansas, Oklahoma). The high diversity and relative rarity of identical sequences among samples were also consistent with dispersal limitation. The exact mechanisms driving its decline are currently unknown, but a combination of dispersal limitation and habitat loss seem likely causes.

Intraspecific competition can significantly alter the foraging behavior of social insects. How competition might impact closely located colonies with overlapping foraging ranges is largely unknown. Between August–November 2022 and September–November 2023, we investigated the intraspecific competition of three Aphaenogaster species (A. famelica, A. schurri, and A. japonica) in two urban forests in Kunming, China. We estimated the density of ant nest openings and measured foraging distances. Nest opening density was 0.18/m² (0.33/m² for A. famelica, 0.03/m² for A. schurri, and 0.07/m² for A. japonica), and mean foraging range was 160 cm (124 cm for A. famelica, 296 cm for A. schurri, and 228 cm for A. japonica). We then ran a series of field experiments to assess the effects of distance, food load, and intraspecific competition on ant foraging. For 36 pairs of nest openings, we placed one light and one heavy tuna bait at various distances between neighboring nest openings. We modified competition intensity by physically blocking one of the nest openings and analyzed time spent on food discovery, removal, and retrieval by ant workers. Ants spent a longer time discovering baits located farther away from, and retrieving heavier or farther baits. Blocking was correlated with a longer time for food removal (for A. schurri/japonica and A. famelica) and transportation (for A. famelica). Selectivity of the light vs heavy bait was not found, suggesting neighborhood distance was too short to generate distance-based selectivity patterns. Differences in nest spacing might be related to species-specific traveling and intraspecific competition.

The high diversity in ants has been associated with some genomic divergences, including karyotype, nuclear genome size and DNA sequences. This study investigated if DNA ploidy levels varies among organs of the worker subcastes of the carpenter ant Camponotus aff. balzani. We also examined if DNA ploidy levels variation may contribute to variations in body size and functional specialization of the worker subcastes and its potential reproductive and behavioral differences among castes. Different DNA ploidy level were identified in the brain, post-pharyngeal gland, thoracic muscles, abdominal sternite muscles and midgut of the workers, resulting in similarities and divergences about the endopolyploid index (EI). The major workers presented the highest EI in the post-pharyngeal gland and thoracic muscles compared to median and minor workers, which may be associated with the different tasks that workers perform in the colony. The lowest EI was found in the brain of all workers subcastes. Moreover, gynes exhibited higher EI levels compared to males and worker subcastes. These findings suggest a complex interplay of genetics and caste determination in this ant. Overall, the results provide fundamental contributions for further studies to verify the role of endopolyploidy in the phenotypic plasticity among castes and subcastes of Camponotus aff. balzani, with potential implications for understanding similar processes in other social organisms.

Division of labour is an important factor of social insect ecological success. However, the specific mechanisms associated with division of labour differ widely between species. Often, social groups have to cope with severe perturbations and resume normal functioning as quickly as possible. How well they do so depends on the behavioural mechanisms involved and on species life-history traits. Here, we studied the division of labour in D. lucida, a threatened species of native Brazilian queenless ants with small colony sizes, to assess whether colonies facing a drastic perturbation of the established task allocation are resilient, and through which potential mechanisms. We first separated the colonies into two sub-colonies, one with the foragers and the other with the nurses. As this is an important modification of colony structure, we expected workers to respond quickly by switching tasks. Our experiment showed that, contrary to our hypotheses, workers showed little plasticity in switching tasks, and colonies did show very limited resilience. Foragers, when isolated from nurses, show a certain plasticity in their behavioural repertoire, performing both tasks (foraging and nursing). However, groups of nurses facing the absence of foragers kept almost exclusively to nursing tasks. Only a few performed episodic outside activities. When workers were returned to their original colonies, foragers switched back to foraging. However, the effect of the manipulation could still be observed 20 days after reintroduction, with workers showing lower general activity, ingesting larvae and reproductive workers losing their dominance. Considering our current knowledge about the regulation of both division of labour and reproductive hierarchies in Dinoponera and other ponerine ants, we propose that this lack of resilience is due to the reproductive conflict between nurses, which delays behavioural maturation and reduces motivation to engage in outside tasks. The existence of individual strategies thus imposes severe costs on group functioning. This could be an additional issue when considering the conservation of this endangered species.

Urbanisation is associated with air and soil pollution, particularly from heavy metals. One of the tissues most exposed to such pollutants is the midgut epithelium as insects may ingest these pollutants with food. Bees are one of the most important urban insects, providing important ecosystem services such as pollination. However, to the best of our knowledge, no studies have investigated the possible histological alterations to the midgut epithelium of bees caused by urbanisation. We sampled workers of the ground-nesting, primitively eusocial bee Halictus scabiosae in a large metropolis (Milan), with the aim to test if individuals from areas characterised by higher urbanisation and consequently higher pollution levels—defined here by a greater proportion of roads—exhibit greater histological tissue and cellular alterations in the midgut epithelium. We obtained semi-thin sections of the midgut through histological techniques, and then adopted a semi-quantitative approach to assess morphological damage. The midgut presented a range of histological alterations including epithelium disorganisation, vacuolisation, and nucleus karyorrhexis (one of the stages of cellular death). We found higher histological damage score (calculated taking into account all found alterations) and frequency of karyorrhectic nuclei in sites with a higher proportion of roads (i.e. more urbanised). The observed alterations may underline a potential impairment of the digestive function in highly urbanised areas.

In mutualistic associations, lycaenid butterfly caterpillars trade nectar secretions against protective services by ants. Eversions of paired abdominal tentacle organs (TO) have been suggested to honestly signal nectar secretion capacity of caterpillars to their ant visitors. Using data from 1561 staged encounters between larvae of nine West Palaearctic Polyommatinae species and worker ants of three species, I show that within experimental series, significantly positive correlations between TO eversion and nectar secretion rate emerged only sporadically (12 of 50 series). In a meta-analysis integrating over all tested species combinations and experimental conditions, the relationship between nectar secretion and TO eversion rate was weak (r² = 6.6%), though significantly positive. This association between myrmecophilous behaviours was not stronger in experiments with feeding mature larvae than in prepupal non-feeding larvae; however, the latter delivered distinctly more nectar. Relationships between nectar secretions and TO eversions were independent of the density of ant partners available and did not vary consistently between lycaenid species showing different levels of myrmecophily. When mean values of nectar secretions per experimental series were related to the respective mean TO eversion rates, a clear positive relationship only emerged among intimately ant-associated species. In moderate myrmecophiles average tentacle activity was unrelated to mean nectar delivery. Overall, these experiments yielded only weak support for the reliable-signalling hypothesis. I propose that TO eversions rather serve as complementary dimension of multimodal communication between partners. ‘Apparent honesty’ may then emerge if caterpillars achieve optimal ant attendance by concomitantly increasing nectar secretion and TO eversion rates.

Stingless bees are a widespread group of highly social bees found in tropical regions throughout much of the world. Despite an impressive diversity, relatively little is known about worker behaviour and division of labour. In this study, we investigate the progression of colony tasks over the lifespan of worker bees in colonies of the two most commonly kept Australian species: Tetragonula carbonaria and T. hockingsi. We marked cohorts of 25–100 newly emerged female bees with a paint dot and released them back into colonies housed in observation hives before recording twice weekly behaviours of marked bees within the nest. Foragers were observed through a clear plastic entrance tube. We replicated this with 5–6 marked cohorts across three colonies for each species. We found the two species were similar to each other in the frequency and age distribution of behaviours. Young worker bees were mostly found cleaning, filling or constructing brood cells and collecting honey from food pots. Middle aged bees were more likely to build or maintain food pots or supporting structures, with guarding and foraging occupying the oldest bees. There was, however, significant overlap in timing of tasks. Moreover, fast cohorts progressed to foraging in less than half the time of the slowest cohorts. Despite subtle differences between our Tetragonula species and other stingless bees, it adds to the evidence that progression from safe to risky jobs with age is an ancestral feature shared across stingless bees, and has similarities to honeybees despite an independent evolutionary origin.

Eusocial aphids produce sterile defensive individuals (soldiers) for colony defense. Because soldier production leads to a trade-off between colony growth and colony defense, to realize stable colony growth, the aphids should produce soldiers in response to a changing predation risk. However, the factors affecting soldier production have been revealed in only three species of eusocial aphids, which altogether comprise 40 species. In this study, we investigated the induction of soldier production in the eusocial aphid Ceratovacuna japonica (Hemiptera: Aphididae) by observing colony growth and the reproductive schedule of C. japonica on its secondary host plant Sasa senanensis (Poales: Poaceae) in the laboratory. We hypothesized that soldier production depended on the number of aphid individuals on the host plant. Our results showed that individuals of C. japonica that had just founded their colony on a leaf of the host plant produced only normal individuals, thereby maximizing the population growth rate. Then, after the number of aphid individuals has increased on the host plant, the adults started to produce soldiers for colony defense. Further, newborn aphid individuals that were moved from a leaf having a colony with soldier production to a new leaf without a colony foundation did not produce soldiers after they grew up. This result suggests that C. japonica can flexibly produce soldiers in response to a change in the number of aphid individuals on the host plant.