Inter- and intraspecific genetic variation in twelve Prymnesium (Haptophyceae) clones

The haptophytes Prymnesium parvum Carter and Prymnesium patelliferum Green, Hibberd, and Pienaar are two closely related species, which can only be distinguished by minor differences in the morphology of their organic body scales. The two Prymnesium species are reported to coexist at several locations, including the Sandsfjord system in southwestern, Norway. Comparisons of physiology and toxicity within the two species have failed to reveal differences that can add to the small morphological distinctions used to separate them. To investigate the genetic relationship between the two species, we compared the sequence of the first internal transcribed spacer region (ITSI) and length variation in one intron separating calmodulin genes for four P. parvum strains and eight P. patelliferum strains. Both the ITSI sequence and the banding patterns obtained by PCR amplification of one intron in the calmodulin genes indicated that the Prymnesium isolates are related by their geographic origin instead of by their species affiliation. The results indicate that P. parvum and P. patelliferum are so closely related that they could be considered one species. Alternatively, we discuss the possibility that the two species might be joined in a heteromorphic haploid-diploid life cycle, as is now widely reported for other haptophycean algae.