Fil: Alma, Andrea Marina. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; Argentina

Termites have evolved diverse defence strategies to protect themselves against predators, including a complex alarm communication system based on vibroacoustic and/or chemical signals. In reaction to alarm signals, workers and other vulnerable castes flee away while soldiers, the specialized colony defenders, actively move toward the alarm source. In this study, we investigated the nature of alarm communication in the pest Reticulitermes flavipes. We found that workers and soldiers of R. flavipes respond to various danger stimuli using both vibroacoustic and chemical alarm signals. Among the danger stimuli, the blow of air triggered the strongest response, followed by crushed soldier head and light flash. The crushed soldier heads, which implied the alarm pheromone release, had the longest-lasting effect on the group behaviour, while the responses to other stimuli decreased quickly. We also found evidence of a positive feedback, as the release of alarm pheromones increased the vibratory communication among workers and soldiers. Our study demonstrates that alarm modalities are differentially expressed between castes, and that the response varies according to the nature of stimuli.

One of the main tasks a freshly mated ant queen has to face is to find a safe and suitable nest site to start a new colony. Colony foundation by associated queens, also known as pleometrosis, has been described for several ant species and, under specific selective pressures, represents an alternative to independent colony foundation. Despite most newly mated queens of the common Mediterranean acrobat ant Crematogaster scutellaris generally adopting independent colony foundation inside tree trunks, both field and laboratory studies have demonstrated that the formation of pleometrotic groups may occur, particularly inside lignified aphid galls on poplar or oak trees. These associations typically end with the survival of only one queen after the foundation phase, and the benefits they may provide remain unclear. In this study, we investigated how queen density and different nest availability may promote the formation of pleometrotic associations in C. scutellaris. We found that occupied nests are not actively sought after by queens, as hypothesised in previous studies, but might be accepted when they are the only safe refugia available. Moreover, the tendency to form groups increases as queen density increases, and nest availability is a limiting factor. Finally, we found no evidence that the size of the queen affects whether to join an already occupied nest.

Social cooperation requires increased tolerance of other individuals. We used social and solitary individuals of the facultatively eusocial bee Megalopta genalis to compare interactions with non-nestmate individuals in a standardized behavioral assay, a circle tube. We set up interactions between bees from different nests matched for caste (solitary, social: queen or worker). We found more tolerance in social than solitary pairs, but found no difference in aggression. We also found that workers continued expressing caste-typical behavior even when matched against other workers from different nests. However, there was no difference in expression of queen-typical behaviors between the three groups. Our data on social caste show that outside of the queen–worker social context, both queens and workers express similar levels of queen-like behavior. However, workers still express higher levels of worker-like behavior than do queens. We found no effect of variation in ovary size on behavior. We found that body size correlated positively with queen-like behaviors, and negatively with worker-like behaviors. Our body size data suggest that the worker phenotype may result from naturally occurring size-correlated variation in behavior, combined with maternal manipulation of both body size through nutrition and behavior and ovary development through social aggression.

Group formation and recognition mechanisms can strongly influence the decision to cooperate or attack in animal societies. Therefore, testing how individuals recognize group membership, and the decision to cooperate or attack during social interactions is critical to understanding the evolution of sociality. We explore decision-making in the weaver ant Oecophylla smaragdina, a highly territorial and also cooperative species. Here, we report a previously undescribed rescue behavior for weaver ants, and determine the role of distance and group membership in residents’ decisions to either rescue or attack conspecifics in distress. First, we tested if residents preferentially rescued nestmates and attacked non-nestmates. Our results show that rescue was more likely for nestmates; however, surprisingly, conspecifics from neighboring colonies were rescued in 43% of the distress trials. Furthermore, attacks became more frequent as distance between colonies increased showing a dear enemy effect, which may be explained by familiarity, odor recognition, and/or relatedness. Our work exploring the factors that influence the decision to rescue or attack provides novel evidence to understand the underlying selective pressures that shape decisions of cooperation or conflict in highly cooperative societies.

In 1882, Metchnikoff documented the encapsulation response (ER) of the invertebrate immune system. Since then, researchers have used Metchnikoff’s method to quantify immune function—and examine its relationship with ecological and behavioral factors—across various insect taxa. While scientists continue to uncover information regarding invertebrate immunity, behavioral ecology, and ecological immunology, the basics of Metchnikoff’s method have remained unchanged. All but two previous studies investigating insect immunity have used sterile or PBS-coated inducers, although we know that the immune system recognizes specific pathogens. To account for the specificity of the immune system, we modified Metchnikoff’s method and coated nylon monofilaments with pathogen-associated molecular patterns (PAMPs). Using honey bees (Apis mellifera), we examined ER using implants coated with PAMPs (“PAMPlants”) found on known honey bee parasites and pathogens. Lipopolysaccharide (LPS), peptidoglycan (PGN), and β-1, 3-glucan (B13G) PAMPlants mimicked an infection with Gram-negative bacteria, Gram-positive bacteria, and fungi, respectively. Our PAMPlants induced stronger responses than the control implants in both singly- (one PBS-coated or PAMP-coated implant) and doubly- (internal control; one PBS-coated and one PAMP-coated implant) implanted animals. In doubly-implanted individuals, there was a significant increase in response to B13G and LPS when compared with internal controls. The PGN and BSA did not differ from the internal controls in the doubly implanted individuals. These methods provide an improvement when exploring responses to specific pathogens and exploring topics within the field of invertebrate ecological immunity. When applied to social systems, these methods can be used to examine the evolution of disease resistance in societies.

Ants are known to have various feeding habits and play important roles in many terrestrial ecosystems. However, little is known about how the feeding habits of each ant species are affected by the environmental changes associated with forest succession. In this study, we examined how feeding habits as well as the species composition and food preference of ants would respond to 105-year-old natural secondary succession of a cool-temperate forest. Stable carbon and nitrogen isotopes and radiocarbon were used to infer the feeding habits. The species richness was not affected by forest stand age. Redundancy analysis indicated that stand age, litter N concentration, and soil microbial respiration had significant relationships with the ant species composition. The bait experiments showed that honey bait became more attractive to ants relative to tuna bait in late succession. This was probably associated with changes in available food resources, such as nectar, during succession. Although the isotopic signatures differed significantly among the sample types (i.e., ant species, canopy leaves, and leaf litter), they were not significantly affected by forest stand age or by the interaction between sample types and stand age. This indicates that the ants showed consistent differences in feeding habits among the species during succession. Our results suggest that despite great changes in vegetation, each ant species would maintain functional roles in C and N flows during forest succession.

Some species of termites evolved an outstanding reproductive strategy called asexual queen succession (AQS), in which the primary queen is replaced by multiple parthenogenetically produced daughters (neotenics) that mate with the primary king. When the primary king is eventually replaced, this time by sexually produced neotenic king(s), sex-asymmetric inbreeding occurs and the queen’s genome is more transmitted than that of the king, thereby increasing the reproductive value of female dispersers, and female-biased population sex ratio is expected. Yet, the life cycle, the breeding system dynamics and AQS modalities differ between AQS species, thereby modifying the relative genetic contribution of primary reproductives in the colony and thus also the equilibrium sex ratio. We estimated colonial and population sex ratio over two consecutive dispersal periods in a French Guiana population of Cavitermes tuberosus (Termitinae) in which the founding queen may be replaced only after colony maturity, some neotenic females may be sexually produced, and some female dispersers arise through parthenogenesis. Colonial sex ratio varied among colonies: primary-headed nests with higher within-nest relatedness produced more females than neotenic-headed nests with lower relatedness among individuals. Over the two dispersal periods, the population investment sex ratio fluctuated around 1:1, thereby confirming that AQS breeding system is not necessarily linked with female-biased sex ratio. The balanced alate sex ratio, combined with the occurrence of sexually produced neotenic queens, is possibly the outcome of a queen-king conflict between the primary reproductives.

Cleptobiosis in social insects refers to a relationship in which members of a species rob food resources, or other valuable items, from members of the same or a different species. Here, we report and document in field videos the first case of cleptobiosis in fungus-growing ants (Atta group) from a coastal, Brazilian Atlantic rainforest. Workers of Mycetarotes parallelus roam near the nest and foraging paths of Mycetophylax morschi and attack loaded returning foragers of M. morschi, from which they rob cultivating material for the fungus garden. Typically, a robbing Mycetarotes stops a loaded returning Mycetophylax, vigorously pulls away the fecal item from the forager’s mandibles, and brings the robbed item to its nearby nest. In our observations, all robbed items consisted of arthropod feces, the most common culturing material used by M. parallelus. Robbing behavior is considered a form of interference action to obtain essential resources needed by ant colonies to cultivate the symbiont fungus. Cleptobiosis between fungus-growing ants may increase colony contamination, affect foraging and intracolonial behavior, as well as associated microbiota, with possible effects on the symbiont fungus. The long-term effects of this unusual behavior, and associated costs and benefits for the species involved, clearly deserve further investigation.

By reacting to local environmental stimuli, ant workers excavate a nest that offers suitable climatic conditions. Workers may face increasing CO2 levels while digging across the soil profile, and it is an open question whether these levels are used as cues during nest excavation. Here, we explored the influence of different underground CO2 concentrations on digging behavior in the leaf-cutting ant Acromyrmex lundii. We first quantified digging rates and transport of excavated material as a function of CO2 levels, ranging from atmospheric values to 11% CO2. The mass of both the excavated soil and the pellets transported out of the digging chamber were quantified. CO2 preferences for excavation were investigated in a second experiment, in which workers were presented with a choice of two digging sites that differed in their CO2 levels, ranging from atmospheric to 4% CO2, and the mass of excavated material was quantified. Digging rates were similar for all tested CO2 levels up to 7%, and only significantly lower for 11%. The transport of excavated soil increased with increasing CO2 levels up to 7%, and then decreased at 11%. Workers preferred digging at 1% CO2 and avoided levels of 4%. We suggest that the observed CO2 preferences are likely driven by the requirements of their symbiotic fungus, and could be one of the reasons why colonies of A. lundii excavate superficial nest chambers.