POPULATION GENETICS OF PHORMIDIUM RETZII (CYANOBACTERIA) MATS IN A HEADWATER STREAM USING RAPD ANALYSIS

Abstract

Casamatta, D. A. & Vis, M. L.Department of Environmental and Plant Biology, Ohio University, Athens, OH 45701 USA.Unidirectional flow of water in lotic ecosystems greatly impacts the gene flow of species, especially non‐motile organisms. This research addresses the genetic variation of the cosmopolitan cyanobacterium Phormidium retzii on a spatial and temporal scale in a headwater stream. Ten permanent plots were demarcated, with the first five spaced 1m apart and the second five 20m from the first set. Individual mats of P. retzii were collected from each plot throughout the growing season (3 sample trips). Random amplified polymorphic DNA (RAPD) markers were employed to examine genetic similarity. The eight primers utilized yielded 87 bands among 29 samples. Distance analysis revealed five groupings, which were not necessarily correlated with sample date or by stream location (upstream vs. downstream). Eight of the 10 samples from the final collection date did group together, to the exclusion of all others. Principle Coordinate Analysis (PCO) revealed two clusters, one of which included all of the samples from the last collecting date to the exclusion of others. Analysis of Molecular Variance (AMOVA) did not show any significant differences between upstream vs. downstream sites, but detected significant (p<0.05) differences in genetic variation between the three sample dates. The genetic variance among dates was 86% and within a given date 14%. We speculate that the genetic similarity of mats on the final date may be from a dominant population upstream with a greater growth rate and samples from the first two dates represent cryptic populations from the previous year.