Nuclear DNA content variation in the freshwater red algal orders Batrachospermales and Thoreales (Florideophyceae, Nemaliophycidae)

A microspectrophotometric investigation of red algae in the exclusively freshwater orders Batrachospermales and Thoreales was initiated to determine the extent of nuclear DNA content variation and to corroborate the alternation of haploid and diploid nuclear DNA contents in gametophyte and sporophyte life history stages. Partial RuBisCO subunit (rbcL) sequences were generated and included in a larger data set for phylogenetic analyses to explore possible correlations between genome size and evolution. Results of rbcL analyses reflected those of previous studies, including the monophyly of the genus Sirodotia and family Lemaneaceae, and paraphyly of Batrachospermum. Static microspectrophotometry and the DNA-localizing fluorochrome DAPI (4′,6′-diamidodino-2-phenylindole) and red blood cell (chicken erythrocytes) standard were used to estimate nuclear DNA contents for 11 species in 6 genera in the Batrachospermales and the Thoreales. Estimated nuclear DNA content values ranged from 0.23 to 3.20 pg. ...