Ant peace and war: DNA, RNA and cuticular hydrocarbons

The ecological success of ants rests on the cooperation within their societies, the colonies, and the strong variation in colony structure further enhances this success. At the one end are colonies with one queen (monogyny) and aggressive behaviour among colonies, at the other end are supercolonies many nests with many queens integrated over large areas and no aggression between non- nestmates. Supercoloniality has become infamous due to the devastating success of some invasive ant species. Not readily explicable by evolutionary theory involving relatedness, the formation of supercolonies and nonaggressiveness has remained an intensely debated problem in social evolution. The aim of the project is to explore three research avenues into mechanisms possibly key to abandoning aggression in ants, using the socially and behaviourally polymorphic species Tetramorium alpestre from its native range. Resources available for this species include the sequenced and annotated genome and transcriptome and the characterisation of the odour bouquet, which ants use to discriminate between nestmates and non-nestmates. We will compare monogynous-aggressive, monogynous-nonaggressive, and supercolonial nests to test various hypotheses relating to three research questions: Are there correlates of nonaggressiveness in (Q1) the genome, (Q2) the transcriptome, and/or (Q3) the odour bouquet? The project is scientifically original. It investigates a non-model species with an outstanding combination of social-biological features, which will add independent information to corresponding data acquired for well-established ant study species. We combine multiple methods to connect social-structure and behavioural variation with polymorphisms at both the genotypic and phenotypic level. This multidisciplinary, integrative approach applied to individual workers of an ant species can elucidate mechanisms potentially involved in supercolony formation. The project will also be relevant to fields such as invasion biology, animal psychology, and possibly behavioural and chemical neurobiology. Finally, to the informed public, the project may be interesting because of the extreme level of cooperation in supercolonies in a competitive world, cooperation is not only a pertinent challenge to science but also one of the eternal phenomena rousing curiosity. The methods to be used to validate the various hypotheses include: sampling of three independent populations representing the social-structure and behavioural polymorphisms of the species; behavioural assays to quantify the aggressiveness vs. nonaggressiveness of three nests per population; reconstructing the social structure of the nests; the next-generation sequencing of 72 genomes and 72 transcriptomes of the same individual workers (24 biological replicates each of monogyny-aggressiveness, monogyny-nonaggressiveness, and supercoloniality); chemical analysis of odour-bouquet compounds; and a broad array of statistical and bioinformatic analyses.

The enourmous ecological success of ants rests on the cooperation within their colonies, and their strong variation in social structure further enhances this success. At the one end are colonies with one queen and aggressive behaviour among colonies, at the other end are supercolonies - many nests with many queens integrated over large areas and no aggression between non-nestmates. Supercoloniality has become infamous due to the devastating success of invasive ant species. Not readily explicable by evolutionary theory involving relatedness, the formation of supercolonies and nonaggressiveness has remained a problem in social evolution. The project's aim was to explore mechanisms possibly key to abandoning aggression in ants and to establish the social-structurally and behaviourally polymorphic high-elevation ant species Tetramorium alpestre as a study system in behavioural, genome, and global-change biology. In detail, correlates with nonaggressiveness were searched for in the genome, the transcriptome, the cuticular-hydrocarbon (CHC) bouquet, the gut microbiome, as well as in the environmental factors temperature and nitrogen availability. We found correlates with nonaggressiveness in the transcriptome - for example, a gene among others known for its association with depression and depression-like behaviour, is upregulated in non-aggressive workers (further exploration needed) - and in environmental factors - lower air temperature and lower nitrogen availability in a habitat correlate with lower aggression, suggesting that aggression may increase due to global-change caused future increases in temperature and nitrogen availability. We did not detect a correlate in genome, CHCs, nor gut microbiome. Among others, we further found that aggression is part of a behavioural syndrome in the species that involves foraging boldness and that a shorter season in high elevation accelerates seasonal change in aggression. Questions for future research made available include how environmental influences on behaviour relate to transcriptomic influences on behaviour and how global-change induced changes of aggressiveness and behavioural syndromes involving aggressiveness will translate into population, community, and ecosystem changes. We highlight the importance of combining fields that have different research traditions such as behavioural biology, ecology, physiology, comparative genomics, and transcriptomics for identifying eco-evolutionary trajectories and of doing so in non-model study systems. The project informed the public on the complexity and plasticity of animal behaviour. The result of increased aggressiveness in context with climate warming and eutrophication will hopefully work towards increasing the readiness of policy makers to make the decisions needed in the face of global change and towards society to accept them. The results might also impact the way society understands and combats supercolonial invasive ants, which are among the top invasive species globally, causing huge economic damage.