Clonal raider ants (Ooceraea biroi) are blind and so have to navigate the world using their sense of smell. Therefore, much of their brain is involved in olfactory processing. New research from The Rockefeller University in New York has looked at how these ants respond to danger using ‘alarm pheromones’.
This new work, submitted for publication in December, focuses on how specific areas of the brain are involved in responding to alarm signals. When an ant senses danger, it secretes pheromones from its mandibular gland, which is a specialised gland located in its head. The colony then responds to these pheromones by evacuating their nest, and taking their larvae with them.
For the mechanism of alarm stimulus processing to be discovered, researchers investigated which glomeruli – the first sites of olfactory processing found in the olfactory bulb – are involved. Given how much of the ant brain is involved in olfaction, the Rockefeller team expected to find hundreds of glomeruli involved. Instead, the study found that, in most cases, only 3 glomeruli were involved, highlighting an unexpected specificity of this response in ants. They found a central sensory hub glomerulus ‘that suggests a simple neural architecture’ translates pheromone detection to behavioural response.
To study the neuronal activity in these ants, GCaMP was injected into the organisms. GCaMP is a protein that will fluoresce green light in the presence of calcium ions – this fluorescence will reflect when neurons are active, as their activity is calcium dependent. By observing the areas of fluorescence, the glomeruli involved could be identified.
The key groundbreaking aspect of the research is studying a colonial insect using transgenics. Transgenic fruit flies (Drosophila melanogaster) have been widespread in research since the 1980s, but do not form colonies. The clonal raider ant was first made transgenic in 2017 using CRISPR, and the nature of the species makes genetic studies far easier. Other ant colonies breed sexually, whereas the clonal raider ants lay unfertilised eggs that develop as clones. By modifying the genes of one ant, you then modify the genes of any eggs that it lays, and therefore making genetic manipulation much more feasible.
The implications of this new work could be fundamental going forward. Not only has it proven that transgenic techniques can be used successfully on ants, it begs the question as to whether such transgenesis is conserved in other species . Evolutionarily, this could provide an indication of how social animals have neurologically evolved to have nesting behaviours.
Disclaimer – this research has not yet been peer reviewed or published.
