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1. An observation of a potentially novel defensive behavior against pesticides: Messor oertzeni build a defensive wall against ant traps in the field (preliminary note)

   PRETENDS EAGLE, TJ: RODRIGUEZ (October 2021, Bulletin of insectology)

   In the course of conducting honey bee experiments on the Greek Island of Lesbos we took the opportunity to observe the reactions of ants, Messor oertzeni Forel (Hymenoptera Formicidae Myrmicinae), to a baited ant trap placed in its main foraging path (active ingredient: sodium cacodylate). Each trap had three entrances and we tested five nests. For 14 days we observed the nests and photographs were taken daily to document our observations. Following a baseline condition in which none of the three entrances were open, one entrance was open. Several days later the entrance we opened was turned 90 degrees away from the main foraging trail and a second entrance was opened and placed in the same orientation as the first entrance (i.e., in the main foraging path). Our observations revealed that for four of the five ant colonies, the ants built a barrier around the opened entrance preventing other ants from entering the trap. The materials they used to bar the entrance was composed of twigs, pebbles and soil. We believe that the apparent ability of ants to avoid the effects of an insecticide by baring the entrance to a bait trap is a novel finding and should be replicated under more controlled conditions. 

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2. Oak Galls Exhibit Ant Dispersal Convergent with Myrmecochorous Seeds

   https://doi.org/10.1086/720283  

   Warren, Robert J.; Guiguet, Antoine; Mokadam, Chloe; Tooker, John F.; Deans, Andrew R. (January 2022, The American Naturalist)

   Ants disperse oak galls of some cynipid wasp species similarly to how they disperse seeds with elaiosomes. We conducted choice assays in field and laboratory settings with ant-dispersed seeds and wasp-induced galls found in ant nests and found that seed-dispersing ants retrieve these galls as they do myrmecochorous seeds. We also conducted manipulative experiments in which we removed the putative ant-attracting appendages (“kapéllos”) from galls and found that ants are specifically attracted to kapéllos. Finally, we compared the chemical composition and histology of ant-attracting appendages on seeds and galls and found that they both have similar fatty acid compositions as well as morphology. We also observed seed-dispersing ants retrieving oak galls to their nests and rodents and birds consuming oak galls that were not retrieved by ants. These results suggest convergence in ant-mediated dispersal between myrmecochorous seeds and oak galls. Based on our observations, a protective advantage for galls retrieved to ant nests seems a more likely benefit than dispersal distance, as has also been suggested for myrmecochorous seeds. These results require reconsideration of established ant-plant research assumptions, as ant-mediated seed and gall dispersal appear strongly convergent and galls may be far more abundant in eastern North American deciduous forests than myrmecochorous seeds. 

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3. Ant nests differentially affect soil chemistry across elevational gradients

   https://doi.org/10.1007/s00040-022-00869-1  

   Sankovitz, M.; Purcell, J. (July 2022, Insectes Sociaux)

   Abstract Ants alter soil moisture and nutrient distributions during foraging and nest construction. Here, we investigated how the effects of ants on soil vary with elevation. We compared moisture, carbon, and nitrogen levels in soil samples taken both within nests and nearby the nests (control) of two subterranean ant species. Using a paired design, we sampled 17 sites along elevation gradients in two California mountain ranges (Formica francoeuriin the San Jacinto mountains andFormica sibyllain the Sierra Nevada). We observed an interaction between soil carbon and nitrogen composition and elevation in each mountain range. At lower elevations, nest soil had lower amounts of carbon and nitrogen than control soil, but at higher elevations, nest soil had higher amounts of carbon and nitrogen than control soil. However, our sampling method may only breach the interior of ant nests in some environments. The nest soil moisture did not show any elevational patterns in either mountain range. Ants likely modulate soil properties differently across environmental gradients, but testing this effect must account for variable nest architecture and other climate and landscape differences across diverse habitats. 

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4. Harvester ant colonies differ in collective behavioural plasticity to regulate water loss

   https://doi.org/10.1098/rsos.230726  

   Gordon, D. M.; Steiner, E.; Das, Biplabendu; Walker, N. S. (September 2023, Royal Society Open Science)

   Collective behavioural plasticity allows ant colonies to adjust to changing conditions. The red harvester ant (Pogonomyrmex barbatus), a desert seed-eating species, regulates foraging activity in response to water stress. Foraging ants lose water to evaporation. Reducing foraging activity in dry conditions sacrifices food intake but conserves water. Within a year, some colonies tend to reduce foraging on dry days while others do not. We examined whether these differences among colonies in collective behavioural plasticity persist from year to year. Colonies live 20–30 years with a single queen who produces successive cohorts of workers which live only a year. The humidity level at which all colonies tend to reduce foraging varies from year to year. Longitudinal observations of 95 colonies over 5 years between 2016 and 2021 showed that differences among colonies, in how they regulate foraging activity in response to day-to-day changes in humidity, persist across years. Approximately 40% of colonies consistently reduced foraging activity, year after year, on days with low daily maximum relative humidity; approximately 20% of colonies never did, foraging as much or more on dry days as on humid days. This variation among colonies may allow evolutionary rescue from drought due to climate change. 

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5. Convergent evolution of complex structures for ant–bacterial defensive symbiosis in fungus-farming ants

   https://doi.org/10.1073/pnas.1809332115  

   Li, Hongjie; Sosa-Calvo, Jeffrey; Horn, Heidi A.; Pupo, Mônica T.; Clardy, Jon; Rabeling, Christian; Schultz, Ted R.; Currie, Cameron R. (October 2018, Proceedings of the National Academy of Sciences)

   Evolutionary adaptations for maintaining beneficial microbes are hallmarks of mutualistic evolution. Fungus-farming “attine” ant species have complex cuticular modifications and specialized glands that house and nourish antibiotic-producing Actinobacteria symbionts, which in turn protect their hosts’ fungus gardens from pathogens. Here we reconstruct ant–Actinobacteria evolutionary history across the full range of variation within subtribe Attina by combining dated phylogenomic and ultramorphological analyses. Ancestral-state analyses indicate the ant–Actinobacteria symbiosis arose early in attine-ant evolution, a conclusion consistent with direct observations of Actinobacteria on fossil ants in Oligo-Miocene amber. qPCR indicates that the dominant ant-associated Actinobacteria belong to the genus Pseudonocardia . Tracing the evolutionary trajectories of Pseudonocardia -maintaining mechanisms across attine ants reveals a continuum of adaptations. In Myrmicocrypta species, which retain many ancestral morphological and behavioral traits, Pseudonocardia occur in specific locations on the legs and antennae, unassociated with any specialized structures. In contrast, specialized cuticular structures, including crypts and tubercles, evolved at least three times in derived attine-ant lineages. Conspicuous caste differences in Pseudonocardia -maintaining structures, in which specialized structures are present in worker ants and queens but reduced or lost in males, are consistent with vertical Pseudonocardia transmission. Although the majority of attine ants are associated with Pseudonocardia , there have been multiple losses of bacterial symbionts and bacteria-maintaining structures in different lineages over evolutionary time. The early origin of ant– Pseudonocardia mutualism and the multiple evolutionary convergences on strikingly similar anatomical adaptations for maintaining bacterial symbionts indicate that Pseudonocardia have played a critical role in the evolution of ant fungiculture. 

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