DNA fingerprinting reveals extensive genetic diversity in a field population of the centric diatom Ditylum brightwellii

Microsatellite markers were developed to examine the genetic diversity of field populations of the centric diatom Ditylum brightwellii. Polymerase chain reaction amplification of two dinucleotide microsatellite loci using DNA extracted from single cell isolates was sensitive enough to identify genetically distinct clones. Each of four culture collection isolates was genetically distinct. Moreover, 23 of 24 isolates obtained from the Hood Canal Basin in Puget Sound, Washington, displayed unique genotypes. The gene diversity of the field isolates is 0.88, indicating that the D. brightwellii population was composed predominantly of unrelated individuals. Maximum growth rates were measured for eight genetically distinct field isolates that were maintained at three light intensities. The growth rates of the isolates differed significantly, indicating that high levels of physiological variability also existed within the population. The results of this study indicate that both extensive genetic and physiological diversity can exist within diatom populations isolated from a single geographical locale at a single time. The observed high levels of diversity are hypothesized to result from the exposure of individual diatom cells to a constantly changing environ-ment and thus to changing selection pressures. The extensive physiological and genetic diversity documented here may help explain how diatoms are able to bloom under a wide range of environmental conditions. Diatoms are a remarkably versatile group of organisms