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 f ield populations of the centric diatom Ditylum brightwellii. Polymerase cha in reaction amplification of two dinucleotide microsatellite loci using DNA extracted from single cell isolates was sensitive enough to identify genet ically distinct clones. Each of four culture collection isolates was geneti cally distinct. Moreover, 23 of 24 isolates obtained from the Hood Canal Ba sin in Puget Sound, Washington, displayed unique genotypes. The gene divers ity of the field isolates is 0.88, indicating that the D. brightwellii popu lation 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 di ffered significantly, indicating that high levels of physiological variabil ity also existed within the population. The results of this study indicate that both extensive genetic and physiological diversity can exist within di atom populations isolated from a single geographical locale at a single tim e. The observed high levels of diversity are hypothesized to result from th e exposure of individual diatom cells to a constantly changing environment and thus to changing selection pressures. The extensive physiological and g enetic diversity documented here may help explain how diatoms are able to b loom under a wide range of environmental conditions.