Nuclear DNA content estimates in multicellular green, red and brown algae: phylogenetic considerations

Abstract

Background and aims: Multicellular eukaryotic algae are phylogenetically disparate. Nuclear DNA content estimates have been published for fewer than 1 % of the described species of Chlorophyta, Phaeophyta and Rhodophyta. The present investigation aims to summarize the state of our knowledge and to add substantially to our database of C-values for theses algae.

Methods: The DNA-localizing fluorochrome DAPI (4', 6-diamidino-2-phenylindole) and RBC (chicken erythrocyte) standard were used to estimate 2C values with static microspectrophotometry.

Key results: 2C DNA contents for 85 species of Chlorophyta range from 0.2-6.1 pg, excluding the highly polyploidy Charales and Desmidiales with DNA contents of up to 39.2 and 20.7 pg, respectively. 2C DNA contents for 111 species of Rhodophyta range from 0.1-2.8 pg, and for 44 species of Phaeophyta range from 0.2-1.8 pg.

Conclusions: New availability of consensus higher-level molecular phylogenies provides a framework for viewing C-value data in a phylogenetic context. Both DNA content ranges and mean values are greater in taxa considered to be basal. It is proposed that the basal, ancestral genome in each algal group was quite small. Both mechanistic and ecological processes are discussed that could have produced the observed C-value ranges.

Fig. 1.

Evolutionary tree constructed from a distance matrix of eukaryotic SSU rRNA sequences and based on ‘substitution rate calibration’. Redrawn from Van der Peer et al. (1996).

Fig. 2.

Summary results of combined analysis using morphological, ultrastructural and large and small subunit rRNA gene sequences for the five classes of green algae and four lineages of embryophytes (liverworts, hornworts, mosses and tracheophytes). Redrawn from McCourt (1995).

Fig. 3.

Phylogram of conjugating green algae based on MP analysis of rbcL sequences. Redrawn from McCourt et al. (2000).

Fig. 4.

Comparison of 2n chromosome complements and estimated 2C nuclear DNA contents in Desmids. See Appendix I for data sets.

Fig. 5.

Comparison of 2n chromosome complements and estimated 2C nuclear DNA contents in charophycean and embryophyte lineages. Data for hornworts, liverworts and mosses from Renzaglia et al. (1995). Data for Charales in Appendix I.

Fig. 6.

Phylogenetic tree of the Ulvales and Ulotrichales inferred from 18S rDNA and rbcL sequence analysis. Redrawn from Hayden and Waaland (2002).

Fig. 7.

(A) Consensus phylogeny for the Dasycladales from analyses of rbcL (Zechman, 2003), and (B) 18S rDNA (Berger et al., 2003) gene sequence data.

Fig. 8.

(A) Phylogram based on 18S rRNA gene sequence analysis, and (B) nuclear DNA contents in members of the Cladophorales/Siphonocladales complex. Numbering (1 and 2) indicates major clades. Redrawn from Hanyuda et al. (2002).

Fig. 9.

Comparison of 2n chromosome complements and 2C nuclear DNA contents in members of the Cladophorales/Siphonocladales complex. See Appendix I for data sets.

Fig. 10.

Mean and range of 2C nuclear DNA contents for species representing eight orders of Chlorophyta included in Appendix I.

Fig. 11.

Comparison of 2n chromosome complements and 2C nuclear DNA contents in species of Chlorophyta included in Appendix I.

Fig. 12.

(A) Molecular phylogeny, and (B) range of 2C nuclear DNA contents in the Phaeophyta. Redrawn from Draisma et al. (2001) and Rousseau et al. (2001).

Fig. 13.

(A) Combined analysis phylogenetic tree using morphological, ultrastructural and gene sequence data, and (B) range of 2C nuclear DNA contents in the Rhodohyta. Numbering (1 and 2) indicates major clades in the Florideophycidae. Redrawn from Freshwater et al. (1994), Saunders and Bailey (1997), de Jong et al. (1998), and Harper and Saunders (2001a, b, 2002).

Fig. 14.

(A) Molecular phylogeny, and (B) estimated 2C nuclear DNA contents and of the coralline red algae. Geniculate genera are indicated by open vertical bars. Note that genicula are non-homologous structures that evolved independently in multiple clades. Geniculate taxa are characterized by larger nuclear genomes (>0·6 pg) and crustose taxa are characterized by smaller (<0·6 pg) with the exception of Neogoniolithon and Titanoderma. Phylogeny redrawn from Bailey and Chapman (1998). DNA content data from J. C. Bailey and D. F. Kapraun (unpubl. res.).

Fig. 15.

Phylogeny for some Corallinales based on the fossil record (redrawn from Wray, 1977) and inferred from 18S rRNA gene sequence analysis (Bailey and Chapman, 1998; Bailey, 1999). Nuclear genome size estimates from J. C. Bailey and D. F. Kapraun (unpubl. res.). Proposed polyploidy events are indicated by [P]. Vertical dashed lines indicate 70 my (million year) intervals. Note proposed polyploidy events and subsequent radiation at the K/T boundary.

Fig. 16.

(A) Molecular phylogeny, (B) and range of 2C nuclear DNA contents in the Ceramiales. Redrawn from de Jong et al. (1998), Phillips (2000) and Zuccarello et al. (2002). The figure in square brackets [ ] represents smallest DNA content (pg) observed in each family. n = number of species and isolates represented by data.

Fig. 17.

Comparison of 2C DNA contents and 2n chromosome numbers for seven species and isolates of Polysiphonia (Ceramiales). Data from Kapraun (1979, 1993b) and Kapraun and Dunwoody (2002).

Fig. 18.

Negative correlation of carpospore volume with the number of carpospores per cystocarp for four orders of Florideophycidae. Regression analysis of data for all orders, r² = −0·512. Without data for the Ceramiales, r² = 0·719.

Fig. 19.

Comparison of 2n chromosome complements and 2C nuclear DNA contents in the Rhodophyta. Data taken from Appendix III.