Predators may play an important role in affecting the fitness of preys. Many organisms have thus evolved strategies to prevent predation. Recognition of predator presence may be achieved by vision, olfaction, tactile sense or detection of water motion. Some organisms sense predators directly; others associate the injuries of victims to the presence of predators. There are many brittlestars (Ophiocoma scolopendrina) at the intertidal zone of Kenting, southern Taiwan and they suffer high frequencies of injuries in the wilds. Since their predators are likely to be diverse, we want to know if O. scolopendrina has the ability to sense the presence of predators, indirectly. We have two hypotheses: firstly, the avoidance behavior is elicited specifically in response to predators, secondly, the avoidance behavior is a general response to unfamiliar elements in the water mass. Our experiments revealed that the tested individuals would avoid conspecific viscera liquids and also that of other echinoderms¡¦. They are more likely to respond to conspecific viscera liquids. And O. scolopendrina hardly respond to solutions prepared from other organisms, e.g., fish, pork, macroalgae, freshwater. This behavior may help brittlestars reduce the probability of encountering predators. The results are compatible with the first hypothesis only. The effect of tide was also explored by testing in different times, but the frequencies of avoidance responses were independent of the tide. Furthermore, the subtidal species Ophiocoma dentata was also tested for the behavior. They escaped from conspecific viscera liquid as well as that of O. scolopendrina. This species, however, could not distinguish the liquids from the two brittlestar species. In conclusion, the avoidance behaviors of the ophiocomid brittlestars are adaptations for avoiding predators, not for avoiding unfamiliar environments.

Regeneration is, in simple terms, ‘to re-grow’ damaged or lost parts of the body (e.g. cells, tissues and organs) and is a natural phenomenon occurring throughout the life of an organism. The regenerative capacity varies in the animal kingdom. Invertebrates have high regenerative capacity in contrast to higher vertebrates. This raises several fundamental questions related to the regeneration potential, evolutionary selection and its cellular and molecular mechanisms. An in-depth knowledge in regeneration is warranted to answer the fundamental questions that are still a challenge in regenerative medicine.  Glycosaminoglycans (GAGs) are known to be involved in various physiological processes. Of several GAG types galactosaminoglycans are the focus of this thesis. Galactosaminoglycans such as chondroitin sulfate/dermatan sulfate (CS/DS) are anionic linear polysaccharides covalently linked to core proteins so called proteoglycans (PGs), and form an integral part of both cell surface and extracellular matrix components. Although CS/DS have been associated with different cellular processes from development to homeostasis, not many studies have been carried out to understand their role in regeneration. In this thesis, we aim to study galactosaminoglycans, their structure, and interaction with growth factors of biological importance in the process of regeneration using simple invertebrate model organisms - brittlestars. We have identified CS/DS as the major GAG present in brittlestars. Molecular characterization of these chains indicated a much higher level of sulfation in Amphiura filiformis than so far found in GAGs from invertebrates or vertebrates. This brittlestar CS/DS promotes FGF2 mediated cell signaling similar to heparin. Further, we studied the functional role of these CS/DS chains and their biosynthetic machinery during arm regeneration in A. filiformis. Regeneration is followed by an increase in GAG sulfation from blastema stage to the fully functional arm. Suppressing sulfation on the other hand by sodium chlorate treatment drastically affected the proliferation process and thereby regeneration. Thus our findings suggest a potential biological role of CS/DS in brittlestar limb regeneration that may have relevance to regenerative medicine in future.

Marine and aquatic species relying on external fertilization must have special adaptation against sperm-dilution in the water. In addition mating competition may be another important source of limitation to an individual¡¦s reproductive success. If the two above mechanisms are in direct conflict, real adaptation would reflect whichever is more critical to one¡¦s fitness. In using the same logic, the unidirectional induction of spawning, i.e., females inducing males, but not males inducing females, has been reported as an evidence for the relative importance of natural selection, that is, sperm-dilution, in limiting the fitness of brittlestars in shallow waters. If the above deduction is correct, one would predict more adaptations to offset the adverse effect of sperm-dilution in various aspects of spawning-related characteristics. Two species of brittlestars. Ophiocoma dentata, living in subtidal zone, and O. scolopendrina, living in intertidal zone, were studied at Kenting, southern Taiwan. Experimental approaches were adopted to figure out if these two species have any adaptation in space and in time that can perceivably counteract the effect of sperm dilution. Spatially, the male O. dentata has the ability to search for females, and the males living with females have higher rates of responding to female spawn than unpaired males; the males do not actively search for eggs released in the water. In O. scolopendrina, neither male nor female had the ability to distinguish the sex of other individuals, they do not form pairs in nature. Males, however, have strong ability to search released eggs and then approach and spawn near the eggs. Temporally, the males of the O. scolopendrina, are sensitive to tidal rhythms in terms of inducibility by female spawns, they only spawn at the time of low tide. The possible effect of water level and photophase were both ruled out. In contrast, no such tidal rhythms of male inducibility was found in the subtidal O. dentata. Sexual selection needs not be invoked in any of the above behaviors, whereas natural selection against sperm dilution is an acceptable explanation. Last, the male O. scolopendrina displays interference behavior by blocking other males from approaching eggs are in the water. The blocked individuals are less likely to spawn.