Diversity and adaptive strategy of submarine cave faunas

本研究旨在阐明从日本到密克罗尼西亚和波利尼西亚的热带西太平洋广大地区的隐栖动物（特别是海绵软体动物）的多样性和适应策略。在此资助下，我们对国内的几个洞穴进行了研究，并对国内外样本（从众多洞穴中获得的生物体和基质）进行了室内研究。通过对微小软体动物的观察和鉴定，阐明了各洞穴双壳类动物的种类组成及其地理分布。发现了100多种海绵状双壳类动物。这些双壳类的显著和独特的特征是微小的尺寸，幼体形态，k选择，与深海物种相似，卵大，繁殖力低，孵育物种优势，生态原始。这些特征肯定是相互关联的，可能是对洞穴环境的共同适应策略的结果。低食物水平肯定是最重要的控制因素。尽管许多问题（特别是物种形成和迁移过程）仍未解决，但洞穴双壳类动物的特征通常表明，当世界上极端少营养条件普遍存在时，适应策略的类型可能是有利的。

This study aims to clarify the diversity and adaptive strategy of cryptic faunas (especially cavernicolus molluscs) in a wide area of the tropical western Pacific from Japan to Micronesia and Polynesia. Research of several domestic caves and indoor studies of domestic and foreign samples (living organisms and substrates obtained from numerous caves) have been carried out with this Grant-in-Aid.As the result of our observation and identification of minute molluscs, species composition of bivalves in each cave and their geographic distribution were elucidated. More than 100 cavernicolous bivalves were identified. Remarkable and unique features of these bivalves are the minute size, paedomorphosis, K-selection, similarity to deep-sea species, large egg size, low fecundity, dominance of brooding species, and ecological primitiveness.These features are certainly related to one another and could have resulted from a common adaptive strategy to cavernicolous environments. Low food levels must be the most important controlling factors. Though many problems (especially the process of speciation and migration) remain unsolved, the characteristics of cave bivalves generally suggest the type of adaptive strategy that could be advantageous, when extreme oligotrophic conditions prevail in the world.