Genetic variability and differentiation in niche components of marine phytoplankton species

Abstract

The acclimated asexual reproduction rates of many clones of Emiliania huxleyi (82), Gephrocapsa oceanica (19), Cyclococcolithina leptopora (31), Prorocentrum micans (28), Dissodinium lunula (22), Thoracosphaera heimi (20), and Gonyaulax tamarensis (83) were measured in several light and temperature regimes. The data were used to determine the amount of genetic variability and the spatial patterns of genetic differentiation in these species. None of the species examined exist purely as clones in nature. Statistically significant genetic variability is found even among clones isolated from single water bottles. The amount of genetic variability in asexual reproduction rates in individual phytoplankton populations ranged from 3 t o 13% (coefficients of variation). There is no obvious relationship between the amounts of genetic variability in the populations and the variability or predictability of the environments from which they were collected. No genetic differentiation was found within the Sargasso Sea in any of the oceanic species, but strong genetic differentiation was found between oceanic and neritic populations of the two species (E. huxleyi and G. oceanica) found on both sides of the Gulf Stream. The spatial patterns of genetic differentiation appear to be different in these two species, however. Genetic differentiation was found between populations from the Sargasso Sea and the slope water off New England is G. oceanica. In E. huxleyi the Sargasso Sea and slope water were similar, but different from the Gulf of Maine populations. Of the three species for which populations were collected at different times of the year (E. huxleyi, C. leptopora, and T. heimi), there is evidence of significant seasonal genetic changes in only one (C. leptopora).