COLONISATION OF THE LAND: A CASE STUDY IN GASTROPODA

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1. Vertical zonation in the intertidal snail Batillaria cumingi, was studied to examine ecological cause of colonization of land in marine gastropoda. The snails found in the highest part of the muddy shore possessed a larger shell with a longer spire than the snails from the lower tidal sites. Based on observations in the laboratory, the former prefers to stay above water to a greater extent than the latter, which corresponds to the difference in their intertidal heights. Among snails transplanted from the upper and lower tidal sites to the position boundary, most moved back to their original sites. Although further genetic analyses are needed, the above results suggest that the preferences for height and air-exposed/submerged condition on a tidal area are diversified within the populations of B. cumingi. This raises the possibility that the vertical zonation in the distribution of Batillaria species has arisen by diversification of habitat preference within populations.2. To estimate patterns of adaptive radiation in Neritopsine gastropoda, mplecular phylogenetic analysis using 28SrRNA sequences was conducted. This group was diversified into marine, flesh water and terrestrial habitat. The inferred phylogenetic relationsip suggests that colonization from marine to ground occur independently at least two times in different lineages and at different times. The ancestral lineages of the terrestrial group are living in marine cave at present. In addition, the colonization from marine to ground occurred through under ground water.3. The rates of molecular evolution were compared by examining nuclear 28SrRNA and mtchondrial DNA sequences in marine and land gastropoda. High evolutionary rates were observed in both 28SrRNA and mtDNA sequences, and thus, colonization of the land follow acceleration in molecular evolution.