The silica cell wall of diatoms (i.e., frustule) is readily preserved in the sediments of most fresh and saltwater ecosystems. These records provide an ecological and evolutionary history of species lineages including both intra- and interspecific morphological variation. Morphological variation in the Stephanodiscus niagarae species complex is well documented. One example of morphological variation in this group is the evolution of Stephanodiscus yellowstonensis from a Stephanodiscus niagarae-type progenitor that is documented from the sediments of Yellowstone Lake. The two species differ in width and number of spines as well as width of ribs. The question here is not “How morphologically different do species need to be?”, but “What portion of morphological variability is attributable to non-genetic versus genetic components?” Here, we test broad sense heritability using quantitative genetics. We subjected clones of three species from the Stephanodiscus niagarae species complex to differing culture conditions (temperature, light, and silica) to determine the proportion of morphological variance that is related to genetic factors, and to explore possible genotype by environmental interactions.
Results/Conclusions
All clones retained normally distributed size, which indicates that no sexual reproduction occurred during our experiment and that our clones are genetically homogenous. All morphological characters tested (number of ribs, width of the ribs, number of spines, width of spines, width of the labiate process, and density of areolae in a striae) showed some proportion of variance related to genetic factors. However, some morphological characters had a large range of intra- and interspecific heritability (e.g. the width of spine had a range of heritability between 0.1644 and 0.8132). However, being that all species and all morphological characters showed some level of heritability indicates that the morphological variance in the Stephanodiscus niagarae species complex is not due to environment alone. Although our analyses are based on estimates of broad sense heritability (which may include effects from dominance and epistasis), our results suggest that the morphological characters in these diatoms may have sufficient genetic variability within and among populations to undergo rapid adaptive evolution in response to changing environments, as S. yellowstonensis apparently did 10,000 years ago.