A molecular re-examination of speciation in the intertidal red algamastocarpus stellatus(gigartinales, rhodophyta) in Europe

Mastocarpus stellatus is a common intertidal red alga in the north Atlantic. Previous work showed that the species was divided into at least two breeding groups in the northeastern Atlantic, a northern one ( absent in Spain and Portugal) and a southern one, which were almost completely inter-sterile. It also showed that, in laboratory culture, at least two types of life history were evident in this species ( a sexual one and a 'direct' one). The distribution of these life histories appeared to have a north - south distribution. We have used molecular markers to confirm these results and expand the sampling in certain populations. Organellar markers showed that the breeding groups have different plastid and mitochondria haplotypes and appear to be distributed along a north - south gradient. Populations in southern England and northern France ( Brittany) have mixed northern and southern breeding groups, except for the Rade du Brest, as was shown previously from culture studies. Results also show that most asexual plants have a plastid haplotype corresponding to the northern breeding group and a mitochondrial haplotype corresponding to the southern breeding group, a possible case of differential organellar inheritance and hybrid formation of an asexual life history. These results using molecular markers support previous conclusions and again emphasize the high levels of genetic variation in marine algae in Brittany.