Coral reefs ecosystems are some of the most productive and diverse in the world. The symbiotic association between cnidarians and their symbiotic microalgae is of great importance in coral reef ecosystems; however, its underlying molecular mechanism remains unclear even after decades of research. Rab small GTP binding proteins are critical regulators of vesicle trafficking. Here we present the experimental evidence supporting a possible association of ApRab37 with the surface of lipid droplets in the endosymbiosis between the sea anemone, Aiptasia pulchella and the symbiotic dinoflagellate (commonly known as zooxanthellae). ApRab37, a protein of 215 amino acids, displays strong homology with human Rab37. In transfected COS7 cells, EGFP-ApRab37 localized to lipid droplets and clustered in the peri-nuclear region, which stained positive for the ER (endoplasmic reticulum) marker. Immunostaining analysis found ApRab37 associated with symbiosomes and lipid droplets, which was also confirmed by Western blot analysis of in the enrich lipid droplet fraction. Phagocytosis assay showed that ApRab37 involved in late phase of phagocytosis. DCMU treatment indicates symbiosome association of ApRab37 is mediated by zooxanthellae. I propose that ApRab37 plays a pivotal role in the regulation of lipid trafficking from the symbiosomes to the host cell during the Aiptasia-zooxanthellal endosymbiosis.

Abstract In order to explore the mechanisms causing trade-offs between sexual and asexual reproductions, the sea anemones Aiptasia pulchella were taken as objects since they can reproduce by both modes simultaneously. Specimens were reared under different temperatures, photoperiods, and densities. Total weights of lacerates were used as an index of investment in asexual reproduction, whereas gonad weights as an index of investment in sexual reproduction. Sea anemones reared under low temperature (22¢J) reached larger pedal disks and produced larger, heavier lacerates, they also produced heavier gonads than those under high temperature (29¢J). Those reared under long light hours (15¡G9) reached smaller sizes and produced heavier gonads than those under short light hours (9¡G15). But the effect of photoperiod on lacerate size, number and weight are not significant. Interaction effect was not significant between these two factors. Correlation between sexual and asexual investments was not significant, either. In addition, A. pulchella reared under low density (1 sea anemone/beaker) produced more, heavier lacerates and heavier gonads than those under crowding conditions (4 sea anemones/beaker). There was a significantly positive correlationship between sexual and asexual reproduction investments. It seems there was no trade-offs between sexual and asexual investiments of the sea anemone A. pulchella.

The effects of energy quantity to the reproductive strategies of the sea anemone Aiptasia pulchella Carlgren 1943 Chien-Hsun Chen (Advisors: Drs. Keryea Soong, Chao-Lun Chen) Institute of Marine Biology, National Sun Yat-Sen University, Kaohsiung, 804, Taiwan, R.O.C. Thesis abstract The influences of energy quantity on the sexual and asexual reproduction and possible trade-offs between them in the sea anemone, Aiptasia pulchella were investigated. Different feeding frequencies, light intensities and presence of zooxanthellae were the treatments of energy quantity. Lacerate numbers, lacerate sizes and total weight of lacerates were used to quantify investment in asexual reproduction; oocyte sizes and gonad weights were used as the measures of sexual reproduction. The correlation between total weight of lacerates and that of gonads provided an opportunity for evidence of trade-offs between sexual and asexual reproduction. Under higher feeding frequencies, A. pulchella produced more and larger lacerates as well as larger oocytes and heavier gonads than under lower feeding frequencies. Under lower light intensities, A. pulchella produced more and heavier lacerates with than without zooxanthellae. Lacerate sizes were influenced by light intensities, presence of zooxanthellae and the interaction of the two factors. At intermediate light intensity (2000 lux), Aiptasia pulchella produced heavier gonads than at 0 lux or 10000 lux. A. pulchella produced heavier gonads with than without zooxanthellae. The oocyte sizes of A. pulchella were also influenced by light intensities, zooxanthellae and the interaction of the two. In both sexual or asexual modes of reproduction, A. pulchella performed better under higher than lower feeding frequencies. There were higher level of asexual reproduction for A. pulchella under lower light intensities with zooxanthellae. A. pulchella achieved the highest levels of fecundity, as an indication of sexual reproduction, under a light intensity of 2000 lux in individuals containing zooxanthellae. There is a positive correlation between sexual and asexual investment under different energy regimes. This is not compatible with the prediction of the trade-off hypothesis.