Phylogeography of Asparagopsis taxiformis revisited: Combined mt DNA data provide novel insights into population structure in J apan

SUMMARY Six intraspecific lineages ( L ineages 1–6) of Asparagopsis taxiformis have been previously established based on mitochondrial cox 2‐ cox 3 intergenic spacer and a partial cox 1 sequences. ‘ L ineage 2’ ( L 2) was suggested to be a recent introduction to the M editerranean S ea, but its source population has not yet been identified. In order to clarify the nature of northwestern P acific populations, we performed extensive sampling in J apan (60 individuals from 16 locations) and molecular phylogenetic analyses based on mitochondrial sequences. Sixteen additional individuals, collected from eight locations in the I ndo‐ P acific, C aribbean, and M editerranean regions, were also analyzed. Combined sequence analyses revealed that the J apanese populations only consisted of L 2. Out of 19 combined haplotypes identified within L 2, two are shared between J apan and the M editerranean S ea and the H awaiian I slands, and 12 were identified as endemic to J apan. Genetic analyses of population differentiation suggested that J apanese populations are genetically isolated from the M editerranean and the H awaiian populations. A genetic disjunction appears to separate two subpopulations within J apan: one between T oi and K agoshima and the other between O jikajima I sland and K agoshima in the K yushu area.