Molecular ecology of marine protistan assemblages.

摘要

Protistan assemblages are mixtures of single-celled eukaryotes, e.g. algae and protozoa, whose members perform vital functions in the marine environment. Protistan diversity revealed by molecular techniques may rival that of bacterial and archaeal assemblages. However, molecular surveys of protistan diversity remain relatively scarce. This dissertation investigated the breadth and meaning of marine protistan diversity through comparative ecological analyses. More than 5,000 18S rDNA sequences were generated, revealing substantial protistan diversity (hundreds of phylotypes) at several locations. These results confirmed the widespread distribution of recently discovered novel protistan lineages, and substantiated claims that many protists appear to be globally distributed. An incubation experiment indicated similar levels of protistan diversity across several time points, but also revealed substantial restructuring of community composition. Quantitative PCR analysis of an ecologically important alga, Ostreococcus sp., demonstrated its month-to-month variability in abundance within the upper euphotic zone. Cluster analysis and non-metric multidimensional scaling identified similarities between protistan assemblages from 5 m and the DCM in the eastern N. Pacific. However, these shallow water protistan assemblages were significantly different from assemblages recovered from the same depths but in different seasons. In addition, all 5 m and DCM assemblages were generally more diverse and composed of significantly different members compared to assemblages collected from 150 and 500 m at the same site. Molecular comparison of protistan assemblages from euphotic and bathypelagic zones in the western N. Atlantic also revealed higher diversity in shallow-water samples. Assemblages from the euphotic zone and the bathypelagic were largely composed of distinct protistan taxa; only 28 of the 324 taxa were found in surface waters and at depth (2500 m). Protistan assemblages from both euphotic and bathypelagic zones were the most diverse at a Gulf Stream station compared to assemblages from two stations in the Sargasso Sea. Molecular surveys are beginning to reveal the dynamic nature of protistan assemblages which my lead to better predictions of ecosystem function and response to environmental change.