If a crayfish wants to know who's boss, it will use its sense of smell. Crayfish (Procambarus clarkii) fight each other and use chemical signals to form stable dominance hierarchies, with the winners becoming dominant and the losers subordinate. In the crayfish's brain, there are two clusters of cells, 9 and 10, containing neurons which process smell. New cells are added throughout an animal's life, which could help in the processing of olfactory signals to work out who's at the top. During her PhD research at Georgia State University, Atlanta, Cha-Kyong Song (now at Ewha Womans University, Korea) and colleagues hoped to find out if social interactions affected proliferation and survival of neurons in these two brain areas by measuring DNA synthesis and cell division in clusters 9 and 10().
The team paired up juvenile crayfish and filmed their behaviour to find out who was dominant, and who subordinate, before examining their brains. While neuron proliferation was the same in subordinates and dominants, newborn neurons were more likely to survive in cluster 9 in dominant crayfish 14 days after their social interaction, even when body growth rate was taken into account. This suggests that social dominance enhances the survival of newborn neurons involved in processing smell, helping crayfish sniff out the opposition.
