Meeting Abstract

S3.9  Tuesday, Jan. 4  Speciation in red algae: current challenges MAGGS, Christine A*; MINEUR , Frederic; Queen’s University Belfast; Queen’s University Belfast c.maggs@qub.ac.uk

Despite recent tantalizing glimpses of speciation processes in red algae we still have little understanding of how red algal populations have diverged following vicariant events. Molecular clocks are still poorly developed and putting approximate dates on the radiation of deep clades is difficult, let alone those of recent divergences. Only recently have microsatellite studies begun to reveal some patterns of restricted gene flow that may indicate the potential for speciation. We will present some case studies of red algae for which we have molecular data and, where possible, have investigated interfertility. The emerging pattern is increasingly one of reticulate relationships among lineages and recently diverged species. For example, the cave-dwelling species Rhodochorton purpureum, in which sexual reproduction is rarely observed, has divergent lineages with different temperature optima (incipient allopatric speciation) but some populations have hybrid ITS2 profiles, a signal of past or recent interfertility. At a deeper level of divergence, in the Caulacanthus ustulatus complex, nuclear, plastid and mitochondrial markers show three well-supported clades (two tropical and one temperate) with divergences between them (e.g. 5% rbcL) similar to genetic distances between species of rhodophytes. However, mitochondrial markers show one tropical species sister to the temperate species, incongruent with tree topology of nuclear and plastid markers (the other tropical species is sister to the temperate species). Moreover, the two tropical species, which have an overlapping distribution, have been shown to be interfertile in laboratory conditions, which suggests that the speciation event was followed by introgression.