A molecular investigation of polymorphism in the North Atlantic red alga Chondrus crispus (Gigartinales)

SUMMARY Seven samples of Chondrus crispus Stackhouse, representing widely contrasting forms from both sides of the North Atlantic, were compared by restriction digestion of their plastid DNA. The similar banding patterns confirmed that the seven forms were conspecific and distinct from Chondrus ocellatus Holmes f. ocellatus from Japan, used as an outgroup. Nucleotide sequences of the internal transcribed spacers (ITS1 and ITS21 and the intervening 5.8S rRNA gene of the nuclear rRNA operon were investigated as a potential indicator of genetic divergence among morphological variants of C. crispus. The combined ITS regions were relatively short in Chondrus (between 719 and 731 base pairs [bp] in C. crispus and 724 bp in C. ocellatus f. ocellatus), and the sequence of the 5.8s rDNA fragment (152 bp) was identical in both species. In the aligned ITS regions, there were 0–18 base pair differences (0–2.18% divergence) in pairwise comparisons of the seven forms of C. crispus but no consistent pattern of variation according to gross morphology or geographic origin. However, the ITS sequence differed at 41–54 sites (6.22-7.56%) between C. crispus and C. ocellatus f. ocellatus, again illustrating the genetic distinctiveness of the latter species.