Distribution of Ciliates in Intertidal Sediments across Geographic Distances: A Molecular View

The estimation of the diversity and geographic distribution of protists in particular ciliates has long been an ongoing debate. We estimated the distribution of ciliates in intertidal sediments with geographic distance ranging from 10cm to 1,000km, using high-throughput DNA sequencing. Higher community similarity, in particular that of rare ciliate taxa, occurred between replicates than between sites. Statistical analyses showed that the community dissimilarities of both abundant and moderately abundant ciliates had correlations with geographic distance at the scales of 50m, 200km and 1000km, indicating a distance-decay relationship. No significant correlation was observed for rare taxa. The analysis of Bray-Curtis similarity showed a higher pairwise community similarity in abundant taxa than in moderately abundant taxa, and that in rare taxa was the lowest. Abundant taxa usually can disperse in a wider range than rare taxa, though their distribution is restricted by distance to some extent. Rare taxa are potentially more sensitive to changing environments, but no distance-decay relationship could be observed. The data indicate contrasting patterns of geographic distribution of the abundant and rare ciliate taxa and a weak distance-decay relationship for relatively abundant taxa at a scale over 50m.