Protist diversity assessment: Comparing microscopy, cytometry and molecular approaches

Abstract

Microscopic eukaryotes (protist) are an essential component of microbial food webs and have a key role in the functioning of planktonic systems. Protists have a high degree of structural and metabolic diversity. During the last years, the advent of cultivationindependent molecular methods has deeply influenced the assessment of aquatic microeukaryotic diversity formerly based exclusively on morphological taxonomy. However, comparative studies between molecular and morphological approaches in natural environments remain rare. Here, we evaluated the planktonic protists biodiversity in a set of 10 high mountain lakes of the Pyrenees using three approaches: morphological diversity, obtained by microscopic analysis; genetic diversity, based on cloning and sequencing of the 18S rRNA gene; and cytometric group diversity estimated from flow-cytometer data. Species richness and inverse Simpson index were compared using a range of similarity values to stablish phylotypes (OTUS) and several taxonomic classification levels to stablish morphotypes. Agreements and discrepancies between the three approaches for measuring protist diversity are discussed