Fig 1.
Procedure used to collect fecal pellets in the aquarium experiment.
(a) Incubation of Tridacna crocea in a glass jar. (b) The fecal pellets (brown dots) expelled by T. crocea.
Fig 2.
Light micrographs of a fecal pellet expelled from Tridacna crocea.
(a) Transparent image and (b) fluorescent image under blue light excitation of a fecal pellet. Scale bars = 100 μm.
Fig 3.
Micrographs of thin sections of a fecal pellet expelled from Tridacna crocea.
(a) A light micrograph of a fecal pellet section showing numerous particles stained with toluidine blue, namely, zooxanthella cells. (b) A transmission electron micrograph of a zooxanthellal cell in a fecal pellet. Scale bar in the light micrographs = 50 μm, and that in the transmission electron micrograph = 1 μm. N, nuclei; Ch, chloroplast.
Fig 4.
Mean Fv/Fm values of the zooxanthellae in the mantle (Mantle) and in fecal pellets (Fecal pt.) of Tridacna crocea.
Bars indicate standard errors for the measured cells (n = 40 ~ 120). Asterisks indicate significant differences among pairs (p < 0.05).
Fig 5.
Fecal pellet expulsion rates of three Tridacna crocea individuals under a light-dark cycle and continuous dark conditions (dark).
Fig 6.
Fluorescence micrographs of Tridacna squamosa larvae provided with zooxanthellal sources.
(a), (b), (c) Larvae in the uptake stage, showing red chlorophyll fluorescence accumulating within the stomach. (d), (e), (f) Larvae in the symbiosis stage, showing fluorescent granules reaching the mantle edge. Scale bars = 100 μm.
Fig 7.
Percentages of Tridacna squamosa larvae in the uptake stage (white bars) and in the symbiosis stage (shaded bars) on the 9th day and 14th day after fertilization.
FIZ, HF(Ts), WF(Ts), HF (Tc), WF (Tc), and SW indicate freshly isolated zooxanthellae, homogenized fecal pellets of Tridacna squamosa, whole intact fecal pellets of T. squamosa, homogenized fecal pellets of Tridacna crocea, whole intact fecal pellets of T. crocea and a negative control, respectively. Error bars indicate standard deviations based on triplicate experimental units. An asterisk indicates a significant difference from the other treatments (p < 0.05, Tukey’s HSD).
Fig 8.
Zooxanthella genus compositions in each zooxanthellal source (averaged across a total of 6 samples).
FIZ, HF (Ts), and HF (Tc) indicate freshly isolated zooxanthellae, homogenized fecal pellets of Tridacna squamosa, and homogenized fecal pellets of Tridacna crocea, respectively. WF(Ts) and WF(Tc) were not analyzed because they were essentially the same as HF(Ts) and HF(Tc). Error bars indicate the standard errors based on six samples.
Fig 9.
Zooxanthellal genus compositions of the Tridacna squamosa larvae incubated with each zooxanthellal source (averaged across triplicate experimental units) 14 days after fertilization.
FIZ, HF(Ts), WF(Ts), HF (Tc), WF (Tc), and SW indicate freshly isolated zooxanthellae, homogenized fecal pellets of Tridacna squamosa, whole intact fecal pellets of T. squamosa, homogenized fecal pellets of Tridacna crocea, whole intact fecal pellets of T. crocea, and a negative control, respectively. Error bars indicate standard errors based on triplicate experimental units.
Fig 10.
Percentages of the zooxanthella population in each Fv/Fm range (averaged over 6 samples).
FIZ, HF (Ts), and HF (Tc) indicate freshly isolated zooxanthellae, homogenized fecal pellets of Tridacna squamosa, and homogenized fecal pellets of Tridacna crocea, respectively. WF(Ts) and WF(Tc) were not analyzed because they were essentially the same as HF(Ts) and HF(Tc). Error bars indicate the standard errors based on 6 samples.