Glass sponges arrest pumping in response to sediment: implications for the physiology of the hexactinellid conduction system
- 527 Downloads
The hexactinellid sponge Rhabdocalyptus dawsoni propagates electrical signals to arrest its feeding current in response to mechanical stimuli and sediment. The deepwater habitat of other species of glass sponge, and the difficulty of working with the tissue in vitro have so far prevented confirmation of electrical signaling in other members of the Class. Here we show in laboratory experiments (ex situ) that mechanical and sediment stimuli trigger immediate arrest in R. dawsoni and in a second species of hexactinellid, Aphrocallistes vastus, suggesting that rapid signaling may be a general feature of glass sponge tissue. Further, responses of the two species differed, suggestive of underlying physiological differences in the conduction system. R. dawsoni and A. vastus were sensitive to sediment but arrests were often prolonged in R. dawsoni, whereas in A. vastus pumping resumed immediately following each arrest. Fine sediment (<25 μm) caused immediate arrests in R. dawsoni and A. vastus, but with a higher stimulus threshold in A. vastus. Large amounts of sediment triggered repeated arrests in both species, and prolonged exposure to sediment (over 4 h) caused a gradual reduction in pumping, with recovery taking up to 25 h. During recovery, both species of sponge carried out repeated arrests, which had a precise periodicity indicative of pacemaker activity. Scanning electron microscopy of the tissue of these specimens showed many chambers were clogged. The results suggest that the glass sponge conduction system generates arrest of the feeding current that prevent uptake of small amounts of sediment, and that each species has different threshold sensitivities. However, ongoing exposure to sediment can clog the filtration apparatus.
KeywordsSponge Body Wall Recovery Event Siliceous Sponge Sediment Addition
We thank the crew of ROPOS and the captain and crew of the JP Tully for exceptional work in collecting specimens, the director and staff of the Bamfield Marine Sciences Centre for use of facilities where this work was conducted, K. Conway (Pacific Geoscience Centre, Sidney, BC.) for providing a sample of sediment from the Hectate Strait sponge reefs, and G. Braybrook for assistance with SEM. GJT was supported by Alberta Ingenuity (AIF) and NSERC PGSD Scholarships. This research was funded by NSERC Discovery and Ship Time grants to SPL. All experiments are in compliance with current Canadian laws on animal care.
- Conway KW, Barrie JV, Krautter M (2004) Modern siliceous sponge reefs in a turbid, siliclastic setting: Fraser River delta, British Columbia, Canada. N Jb Geol Palaont Mh 6:335–350Google Scholar
- Josephson RK (1985) Communication by conducting epithelia. In: Strumwasser F, Strumwasser MJ (eds) Comparative neurobiology: modes of communication in the nervous system. Wiley, New York, pp 133–148Google Scholar
- Mackie GO (1979) Is there a conduction system in sponges? Colloques Int du CNRS 291:145–151Google Scholar
- Yahel G, Eerkes-Medrano DI, Leys SP (2006) Size independent selective filtration of ultraplankton by hexactinellid glass sponges 45:181–194Google Scholar