MULTIPLE POPULATION BOTTLENECKS AND DNA DIVERSITY IN POPULATIONS OF WILD STRIPED BASS, MORONE-SAXATILIS

Striped bass, Morone saxatilis, in the Coos River, Oregon, are derived from natural colonists from San Francisco Bay, which in turn were int entionally transplanted from the Hudson River. Because of founder effe cts, this unusually well-documented colonization sequence should have resulted in diminished genetic variability in the penultimate and ulti mate populations, which may have been further compounded in the Coos R iver population by subsequent drastic reductions in its abundance. To test whether these sequential bottlenecks reduced genetic diversity we surveyed both nuclear DNA (nDNA) and mitochondrial DNA (mtDNA) variat ion in the Coos River population and in both populations along the his torical pathway that led to its founding. There was no evidence of red uced nDNA diversity among these populations at the three loci examined . However, the number of mtDNA haplotypes revealed decreased from 8 in the original Hudson River population, to 5 in the San Francisco Bay p opulation, to only 1 in the Coos River population. This pattern of con served nDNA diversity and reduced mtDNA diversity is consistent with a recent population bottleneck. Coos River striped bass have shown incr easing levels of pathological hermaphroditism. We speculate that the r educed genetic diversity of the Coos River striped bass population may have led to a depensatory cascade involving hermaphroditism that inhi bited reproduction and recruitment, followed by in creased levels of i nbreeding as the population declined.