Colonial Choanoflagellates and Choanocytes in sponges

Sponges are one of the earliest ancestors of the animal kingdom, and choanoflagellates are a close cousin of sponges. Studying their biophysics may help us unravel the mystery of the origin of multicellularity. For example, are there particular reasons why some choanoflagellates remain singular, but some form colonies? How do these cells coordinate without a nervous system? Why do some choanoflagellates form colonies in the shape of a sphere, like a Choanocytes chamber? While not all questions can be answered purely by physics, looking into the mechanics of their movement and fluid flow around them surely helps biologists better understand the evolutionary reason behind their formation and behaviour.

Our recent work studies a recently discovered choanoflagellate _Choanoeca Flexa_. This fascinating multicellular species forms a sheetlike structure that dynamically interconverts between two hemispherical forms of opposite orientation, raising fundamental questions as to why they form such a structure and how they perform the inversion. In the work, we developed a fluid model of their swimming and pumping of feeding current through the sheet. Using the reciprocal theory in Stokes flow, we demonstrated that the inversion between the two hemispherical forms helps them switch between two contrasting configurations, in which the flagella-out form benefits swimming speed, and the flagella-in form benefits feeding.