Intraspecific sterility barrier confirms that introduction of Sphaerotrichia divaricata (Phaeophyceae, Chordariales) into the Mediterranean was from Japan

Crossing studies revealed an intraspecific sterility barrier on the level of zygote formation between Japanese Sphaerotrichia divaricata and isolates of the same species from the Northeast Pacific and the North Atlantic. Because no consistent morphological differences exist between sporophytes from Japan and other areas, the authors propose not to distinguish the intersterile populations as different species. Japanese Sphaerotrichia and isolates from a recently detected population in the Etang de Thau, French Mediterranean coast, are interfertile. The crossing studies support the assumption that this Mediterranean population is a recent introduction from Japan.