TEMPORAL PATTERNS IN POPULATION GENETIC DIVERSITY OF PROROCENTRUM MICANS (DINOPHYCEAE)1

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Abstract
We describe temporal changes in the genetic structure of populations of the dinoflagellate Prorocentrum micans Ehrenberg over a period of 2 years at Scripps Pier (La Jolla, CA, USA). We collected 12 water samples over the course of two blooms and analyzed 166 single‐cell isolates using randomly amplified polymorphic DNA analysis. Six PCR primers uncovered 27 polymorphic markers, allowing the identification of 40 unique haplotypes. Analysis of molecular variance demonstrated that >92% of the genetic variance was partitioned within water samples, providing evidence of high levels of genetic diversity and possibly sexual reproduction. Although the level of genetic diversity remained fairly stable over the sampled time interval, several populations (sampled in June 1998 and March 1999) exhibited significantly different genetic composition, demonstrating differences among bloom and nonbloom periods. About 40% of the isolates in each sample were identified as one haplotype, suggesting that a genetically distinct subgroup was a common member of the populations during the sampled periods. The composition of the remaining isolates was genetically diverse and changed over time, indicating rapid responses (days) to changing environmental conditions or extensive genetic spatial patchiness (kilometers). Within the limitations of our sampling, these two genetically distinct groups appear to exhibit different population dynamics (one stable and the other variable), suggesting that genetic diversity may be closely linked to the change in abundance of phytoplankton on ecological time scales.