51.2 Thursday, Jan. 5 Evidence for a Functional Sensory System in Sponges FARRAR, N*; LUDEMAN, D; LEYS, S; University of Alberta; UAlberta; UAlberta firstname.lastname@example.org
Sponges (Porifera) lack a nervous system, yet both larval and adult sponges are able to respond to external stimuli: glass sponges (hexactinellids) arrest the feeding current to prevent uptake of sediment and demosponges contract their canals in a rhythmical way to expel unwanted waste. One stereotypical behavior is an Inflation/Contraction (I/C), or ‘sneeze’-like action that occurs in response to mechanical stimuli, and can be triggered by 75uM L-glutamate. As sponges were the first multicellular animals to evolve they are ideal organisms for exploring the physiology of the earliest sensory systems. Sponges have flagella on choanocytes, but the presence of cilia in canals is less well known. Here we show cilia line the epithelia of oscula in all 5 demosponges we have studied. The distribution and orientation of the cilia in the freshwater sponge Ephydatia muelleri suggests they function as flow sensors in the canal system. Their presence at the excurrent vent of the aquiferous system implies they may be involved in controlling or triggering the I/C response that demosponges use to expel wastes. To test this we used the aminoglycosidase antibiotic Neomycin sulfate and the steryl dye FM1-43, which disrupt signaling by primary cilia in other metazoans, and found both drugs depressed the I/C response relative to controls. Signaling through primary cilia in other organisms is known to involve Ca2+ influx. Cilia were longer in treated sponges than in controls, providing evidence that the drugs block calcium channels in the cilia and interfere with intraflagellar transport as in other animals. Using Ca2+ imaging we found that in E. muelleri the I/C response is accompanied by a rise in Ca2+ which travels as a wave along the epithelium of the canal system corresponding to waves of contraction. We hypothesize that signaling through primary cilia in the osculum controls contraction of the canals by generating a Ca2+ wave.