Phenotypic and genetic structure of interbreeding populations of the diatomTabularia fasciculata(Bacillariophyta)

Kaczmarska I., Ehrman J.M., Moniz M.B.J. and Davidovich N. 2009. Phenotypic and genetic structure of interbreeding populations of the diatom Tabularia fasciculata (Bacillariophyta). Phycologia 48: 391–403. DOI: 10.2216/08-74.1.Diatom alpha-taxonomy heavily relies on the discontinuity in variation of species-specific structures in siliceous components of the cell wall. However, considerable intraspecific variability of valve morphology is to be expected because of the peculiar mode of diatom valve genesis during the tenure of the asexual part of the diatom life cycle. Here we evaluated variation in valve morphology among 66 Canadian and three Ukrainian clones of the diatom Tabularia fasciculata. Valve length, width, number of striae in 10 µm and number of rimoportulae per valve were enumerated for all clones. Forty-five Canadian and three Ukrainian clones were crossed and their sexual identity determined. Nuclear internal transcribed spacer 2 and 5.8S rDNA gene sequences were used to evaluate genetic variability of the clones. Our data show consistent phenotypic (at least two phenodemes ‘n’ and ‘w’) and genetic (two genodemes, ‘A’ and ‘B’) differentiation within one gamodeme (sexually compatible clones) in Canadian populations of T. fasciculata. The distribution of phenogenodemes is not continuous, even or random; a specific morphology strongly correlates a specific genotype, A and B, both members of the same gamodeme, with just a few exceptions. Specifically, width, striae density and rimoportulae number conform well (though not perfectly) to a specific genotype; only four mismatches were found among clones examined. Crimean members of the n phenodeme were morphologically and genetically very similar to those in Canada despite separation by thousands of kilometers. This is the first documented relationship between pheno- and genotype for an araphid species for which morphological, molecular and breeding data are also provided.