A molecular investigation of polymorphism in the North Atlantic red algaChondrus crispus(Gigartinales)*

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Abstract
SUMMARY: Seven samples ofChondrus crispusStackhouse, 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 fromChondrus ocellatusHolmes f.ocellatusfrom 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 ofC. crispus.The combined ITS regions were relatively short inChondrus(between 719 and 731 base pairs [bp] inC. crispusand 724 bp inC. ocellatusf.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 ofC. crispusbut 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%) betweenC. crispusandC. ocellatusf.ocellatus, again illustrating the genetic distinctiveness of the latter species.