Molecular phylogeny, phylogeography and population genetics of the red seaweed genus Asparagopsis
The red seaweed genus Asparagopsis Montagne (Bonnemaisoniales) was studied
with respect to its taxonomy, phylogeny, phylogeography and population genetics. The
representatives of this genus, A. armata Harvey and A. taxiformis (Delile) Trevisan, are
notorious invaders. Both species occur worldwide and show disjunct distribution patterns.
Such patterns may result from recent jump-dispersal or from fragmentation of once panglobally
distributed species. First, a phylogeographic approach was deployed in order to
delineate the taxonomic units in local scale and to assess if European populations of each of
the species originated from a single introduction or multiple cryptic ones. Results showed
that the two species recognized A. armata and A. taxiformis are also genetically distinct.
Asparagopsis armata was found to consist of a single species worldwide, whereas A.
taxiformis constituted three and probably four morphologically cryptic but genetically
distinct lineages. At times, lineages were encountered in sympatry and two of them were
detected in the Mediterranean Sea.
In order to confirm distinction between lineages and to assess invasive potential and
colonization mechanisms of the species along the western Italian coast, eight nuclear
micro satellite markers were identified against the invasive lineage 2 of A. taxiformis. The
markers cross-hybridised only with lineages I and 2. Moreover, it was demonstrated that
carpogonia present on many female thalli can affect microsatellite reading patterns because
of external (male) allelic contribution. Even after removal of the carpogonia, gametophyte
thalli exhibited multiple allelic patterns, which is indicative for polyploidy. The markers
were then used to assess genetic structure and diversity within and among Mediterranean
populations of A. taxiformis lineages 1 and 2. Analyses based on statistics developed for
polyploid species showed that the lineage l-population (HAW) was distinct from
Mediterranean lineage 2 populations. A geographically distant Californian lineage 2·
population was genetically distinct from the Mediterranean ones as well. The
Mediterranean lineage 2-samples showed panmixia. High genotypic diversity, high gene
flow, and low differentiation encountered amongst these populations probably are due to a
recent invasion of this lineage into the basin.