Size-independent investment allocation to regeneration and growth of the branching coral Acropora muricata
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概要
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To reveal the optimal resource allocation among regeneration, growth, sexual reproduction, and survivorship in a colonial animal, a specimen of the branching coral Acropora muricata (formosa), without oocytes, was separated into fragments of three different sizes (5, 10, and 20cm long) that were then transplanted onto coral pavement. Regardless of the fragment size, a wound was fully closed within 11 days after fragmentation. The number of newly formed polyps on the new tissue layer did not differ significantly among fragment sizes. No significant difference was observed in the monthly growth rate among the three fragment sizes. These results showed that regeneration and growth were independent of fragment size. During the observation period, one 5cm fragment died, the 5cm and 10cm fragments did not spawn, but the 20cm fragments did spawn. The investment to survivorship by the 5cm fragments might have been smaller than that of the 10cm fragments, because the 5cm fragments had smaller energy stocks than did the 10cm fragments. Combined, these results suggest that the energetic investment for regeneration and growth was constant while investment for reproduction was proportional to fragment size. This finding agrees with the theoretical optimal dispersal strategy, in which the allocation to growth by mothers is constant. In conclusion, the colonial coral Acropora muricata generally shows size-independent growth and regeneration, and exhibits a tradeoff among regeneration, growth, survivorship, and reproduction.