Nuclear DNA and karyotype variation in species of Codium (Codiales, Chlorophyta) from the North Atlantic

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Abstract
Chromosome numbers for three species of Codium from Bermuda are presented. C. decorticatum (Woodward) Howe, C. intertextum Collins and Hervey, and C. taylori Silva were found to have chromosome complements of 2N - 20 and similar karyotype patterns. Two DNA-localizing fluorochromes with epi (incident) UV illumination were used to determine relative nuclear DNA in the Bermuda specimens as well as in C. decorticatum, C. isthmocladium Vickers, and C. fragile subsp. tomentosoides (van Goor) silva from coastal North Carolina. Results from microspectrophotometry with mythramycin and hydroethidine, and estimates of nuclear and genome volume demonstrate a wide variation in DNA content among the five species examined. C. fragile subsp. tomentosoides, which is haploid with 1N = 10, has relatively large chromosomes and the largest nuclear DNA content. Interspecific DNA variation is discussed in terms of cryptopolyploidy by lengthwise amplification of the basic genome, differential polynemy and somatic endoreduplication. In addition to revealing wide interspecific variation among Codium species, microspectrophotometric data were obtained for DNA content fluctuations associated with DNA synthesis, meiosis, and endoreduplication.