Phylogeny, Phylogeography and Population Connectivity of Lessonia (Phaeophyceae)
The brown algal genus Lessonia is distributed in the Southern Hemisphere where it can form dominant kelp beds on the exposed rocky shores of New Zealand, South America and Tasmania. Its disjunct distribution within the West Wind Drift contrasts with the view that it is a poor disperser. Apart from studies in Chile, where it is an economically important genus, little is known about Lessonia and in some areas even the number of species is unknown. Using different genetic markers I examined the phylogeny, phylogeography, and the connectivity of populations in Lessonia. Using the literature, species affiliations and nomenclatural problems have been investigated. Combining the sequences of three mitochondrial, one chloroplast and two nuclear markers, a supermatrix approach was used to investigate the phylogenetic relationship and the timing of speciation for all known Lessonia species. The Australasian Lessonia species form a clade within a paraphyletic grouping of South American species. Radiation in Lessonia occurred about 5 Mya at the beginning of the Pliocene and rapid radiation took place in Australasia 3.5 Mya. The data also revealed cryptic species within a L. variegata species complex. Further analysis within the Australasian clade, using mitochondrial (atp8-sp) and chloroplast (rbc-sp) markers and wider sampling (469 individuals from 57 sample sites) supported four cryptic species and revealed localized distribution for all Australasian lineages. Genetic breaks between Lessonia lineages corresponded well to known biogeographic regions and could be correlated to the geographic structure of New Zealand at the end of the Pliocene. The Cook Strait region was analysed more closely with newly developed microsatellite markers to test the influence of geographic breaks (Cook Strait and Palliser Bay) on the connectivity of populations. The results suggested that connectivity depends on the width of unsuitable habitat, and within inner Cook Strait it is facilitated by sometimes strong tidal flows that create turbulences and unique current patterns. The results implied that rafting is an important mean of dispersal. The study of the early literature on Lessonia supported the new lectotypification of L. flavicans but revealed that L. frutescens and possibly L. ovata (supported by images of rediscovered herbarium material) are synonymous to L. searlesiana and as the older epithets they should have priority. Suggestions have been made for the lectotypification of L. fuscescens and L. ovata. In general Lessonia shows non-overlapping distribution in Australasia but overlapping distribution in South America. Despite being a poor disperser, indicated by fine scale genetic structure, Lessonia is also able to connect populations over wide areas of unsuitable habitats.