Gut throughput dynamics in the appendicularian Oikopleura dioica

Oikopleura dioica is an excellent model for studying food flow through the digestive system because of its transparency, non-motility and because feca l pellets move along the digestive system in an orderly sequence which can be easily timed. By observing fecal pellet circulation within the gut of he althy individuals, we have concluded that the average number of fecal pelle ts inside the gut of O. dioica is 2.878 +/- 0.015 (mean +/- SE, n =43). Thu s, gut passage time (GPT, min) can be estimated from the time interval betw een successive fecal pellets (DI, min fecal pellet(-1)) as GPT = 2.878 DI. This establishes the basis for estimating GPT from simple fecal pellet prod uction rate incubations, and is one way of determinating GPT without manipu lating food concentration or quality, a major shortcoming of current techni ques. In laboratory experiments, GPT of O, dioica was independent of body s ize. At 15 degrees C, GPT (min) decreased with increasing food concentratio n (FC, mu g C 1(-1)) when the prymnesophyte Isochrysis galbana (4.5 mu m in size), the prasinophyte Tetraselmis suecica (10 mu m) or the chlorophyte C hlorella sp. (3 mu m) were used as food, according to the power function GP T = 29.4 FC-0.245. There were no significant differences in GPT between alg al types. The GPT of O. dioica exhibited a Q(10) of 0.687 over a temperatur e range of 10 to 20 degrees C, independent of food concentration. Since the interaction between food concentration and temperature was not significant , GPT can be estimated as GPT = 51.67e(-0.0376t) FC-0.245.