The Superorganism’s Circulatory System: Collective control of development through a socially exchanged fluid*

How can a distributed system like a social insect colony collectively decide how to allocate resources and mature over the long-term? Many but not all species of social insects engage in the social fluid exchange of trophallaxis. In species that perform ample trophallaxis, each individual within the colony is connected through the trophallactic network, including larvae. In carpenter ants, we’ve shown that components of trophallactic fluid can influence larval development, regulating the number of new adults produced. Furthermore, we find that some trophallactic fluid proteins have been co-opted from typical insect developmental pathways: as these proteins have become abundant in this social fluid, they show increasing signatures of adaptation such as repeated duplications and positive selection. Recent advances using long-term fluorescence imaging reveal how the content and timing of larval feeding through trophallaxis controls growth and developmental timing. Thus, in species that engage in this behavior, trophallaxis and trophallactic fluid present a means by which adults can regulate larval development according to the needs of the colony.