Choanocyte dimensions and pumping rates in the demosponge Halichondria panicea

The individual choanocyte pumping rate in choanocyte chambers (CCs) is important for understanding the hydrodynamics in sponges and has hitherto been based on measured volume-specific filtration rate and estimated CC density. However, the CC density may vary in different regions of the sponge and to circumvent this uncertainty and to get precise measurements of the individual choanocyte pumping rate, a new experimental approach was developed. Here the aim was to measure the individual pumping rate of choanocytes based on live dimensions of CC elements and particle tracking to measure the speed of small particles entering into the CCs. This was done by using combined live-cell imaging in sandwich cultures of the marine demosponge Halichondria panicea and video-tracking of particles. Small 2pm-beads and cyanobacteria (Cyanobium bacillare) in the incurrent canal enter the CCs via a 3.3 +/- 0.9 pm diameter prosopyle to be subsequently captured by the choanocytes whereas larger algal cells (Rhodomonas salina) and 10 pm-beads are captured in the incurrent canals. CC diameters were positively correlated to the diameter of choanocytes, indicating a total of 84 choanocytes per CC with mean diameter 22.9 +/- 6.2 pm. The pumping rate per choanocyte (Qc) was estimated to be between 54 and 68 pm3 s-1. Regardless of demosponge species and based on data in the literature, a choanocyte is suggested to pump between 50 and 100 pm3 s-1.

Automated summary

This study developed a new experimental approach to measure the individual pumping rate of choanocytes in sponges. By using live-cell imaging and particle tracking, the researchers were able to accurately measure the pumping rate of choanocytes based on the live dimensions of choanocyte chambers. The results showed that each choanocyte pumped between 54 and 68 cubic micrometers per second.