cpDNA-RFLP in Ceramium (Rhodophyta): Intraspecific polymorphism and species-level phylogeny

Restriction fragment length polymorphism (RFLP) analysis of chloroplast (cp ) DNA is a powerful tool for the study of microevolutionary processes in la nd plants, yet has not previously been applied to seaweed populations. We u sed cpDNA-RFLP, detected on Southern blots using labeled total plastid DNA, to search for intraspecific and intrapopulational cpDNA RFLP polymorphism in two species of the common red algal genus Ceramium in Ireland and Britai n. In C. botryocarpum one polymorphism was detected in one individual among 18 from two populations. Twenty-six individuals of C. virgatum from five p opulations at three locations exhibited a total of four haplotypes. One was frequent (80.8% of individuals); the others were rare (7.7, 7.7 and 4.2%) and were private to particular populations. Polymorphism was observed in tw o populations. The corrected mean was 2.26 +/- 0.36 haplotypes per populati on, which was within the typical range determined for higher plants using s imilar techniques. The spatial distribution of haplotypes was heterogeneous , with highly significant population differentiation (P = 0.00018; Fisher's exact test). Intraspecific polymorphism in C. virgatum had no impact on sp ecies-level phylogenetic reconstruction. This is the first unequivocal repo rt of both intraspecific and intrapopulational cpDNA-RFLP polymorphism in a lgae.