SPECIATION IN THE ARTEMIA GENUS - MITOCHONDRIAL-DNA ANALYSIS OF BISEXUAL AND PARTHENOGENETIC BRINE SHRIMPS

From the cloned mitochondrial DNAs (mtDNAs) isolated from two bisexual species, one Mediterranean, Artemia salina, and one American, Artemia franciscana, and two parthenogenetic (diploid and tetraploid) strains of Artemia parthenogenetica collected in Spain, physical maps have be en constructed and compared. They are extremely different among themse lves, much more than the differences between Drosophila melanogaster a nd D. yakuba and in the same range of different mammalian species such as mouse/rat or man/cow. The nucleotide sequences of two regions of m tDNA encoding parts of the cytochrome c oxidase subunit I (COI) and cy tochrome b (Cytb) genes have been determined in the two bisexual speci es and the two parthenogenetic strains. Comparisons of these sequences have revealed a high degree of divergence at the nucleotide level, av eraging more than 15%, in agreement with the differences found in the physical maps. The majority of the nucleotide changes are silent and t here is a strong bias toward transitions, with the C <-> T substitutio ns being highly predominant. The evolutionary distance between the two Artemia parthenogenetica is high and there is no clear relationship w ith any of the bisexual species, including the one present nowadays in Spain. Using a combination of molecular (mtDNA) and morphological mar kers it is possible to conclude that all of these Artemia isolates sho uld be actually considered as belonging to different species, even the two Artemia parthenogenetica diploidica and tetraploidica.