為了提高生殖效率，體外受精的海洋生物須採取各種方式來降低配子被釋出後在海水中被稀釋的風險，另一方面競爭配偶也可能是重要的限制個體成功生殖的機制。我們想了解對這些種類，天擇、性擇何者是比較重要的推動演化機制，又在不同海洋棲地生活之種類有否差異。本研究之對象為台灣南部墾丁珊瑚礁海域亞潮帶生活的齒櫛蛇尾Ophiocoma dentata和潮間帶生活的蜈蚣櫛蛇尾O. scolopendrina。已知此兩種類卵巢含有性費洛蒙可以誘導同種雄性排精生殖，由於性費洛蒙本身不是未受精卵存在的最佳指標，我們想瞭解櫛蛇尾是否已有進一步的適應來增進其生殖機會，而其機制是天擇或性擇，又其生殖適應是否可反映出兩種櫛蛇尾生活棲地之差異。實驗結果顯示在空間上，亞潮帶生活的齒櫛蛇尾，雄性有能力尋找雌性個體，並和雌性共居時有較高的被誘導排精率，但對於水中已釋出的卵，並沒有趨向性；潮間帶生活的蜈蚣櫛蛇尾，兩性皆無辨識其他個體性別之能力，但雄性對於已釋放出的卵，有強烈的搜尋並趨近之能力。另外在時間上，潮間帶生活之蜈蚣櫛蛇尾，雄性排精時間對於潮汐週期具有相當敏感性，會選擇在每日低潮時期受誘導排精，且和當時水位高低及日光週期無關；而亞潮帶的齒櫛蛇尾，雄性被誘導排精之行為則全然不受潮汐週期變化之影響；這些生殖適應明顯的反映出兩者生活環境上之區別，而且顯然是受天擇影響而產生。另外，在潮間帶之雄性蜈蚣櫛蛇尾在趨向水中卵時，先行排精的雄性會阻擋之後才趨近的雄性，而被阻擋的雄性則多採取放棄排精的現象，顯示仍有性擇影響的適應產生。

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.

壹、前言 -1
貳、材料與方法 -6
參、結果 -11
肆、討論 -17
參考文獻 -26
附錄 -46

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