Although reports of geographical parthenogenesis from land and freshwater are numerous, this occurrence has been rarely reported from the sea.īrown algae (class Phaeophyceae, Stramenopiles) are one of the lineages to have evolved complex multicellularity (Cock et al., 2010) and most of them are exclusively marine. The loss of sex (or success of parthenogens) in these particular environmental settings has been a topic of interest in evolutionary biology, shedding light on the cost and benefit of sex, adaptation to marginal habitats, and the role of hybridization and polyploidy (e.g Bierzychudek, 1985 Hörandl, 2009 Kawecki, 2008 Kearney, 2005 Lynch, 1984). Parthenogens often have a biased distribution towards particular environmental settings (e.g., high latitude, high altitude and deserts) when compared with close sexual relatives (Kearney, 2005). An important ecological pattern is geographical parthenogenesis, a phenomenon where parthenogens and their close sexual relatives occupy distinct geographical areas. This parallel loss of the sexual trait may represent the direct origin of parthenogens, or the regressive evolution of a useless trait under asexuality.Īlthough sexual reproduction is the predominant mode of reproduction in nearly all multicellular organisms, organisms reproducing only by parthenogenesis (obligate parthenogens) are numerous. Interestingly, we found that the production of sex pheromones, which attract male gametes, has been independently lost in the initial two parthenogenetic lineages.

The origin of the initial parthenogens is not clear, except that it would not be interspecies hybridization.

Population genetic and phylogenetic analyses, including those based on genome-wide single nucleotide polymorphism data, indicated that parthenogens have initially evolved at least twice and subsequent hybridizations between the parthenogens and sexuals have generated multiple new parthenogenetic lineages. In the two localities where sexual and parthenogenetic populations were parapatric, parthenogens grew in more wave-exposed areas than sexuals. Sex ratio investigation demonstrated that, in Japan, sexual populations grew in the coast along warm ocean currents, whereas female-dominant parthenogenetic populations grew mainly in the coast along a cold ocean current. Here we report a novel pattern of geographical parthenogenesis in the isogamous brown alga Scytosiphon lomentaria. Brown algae are mostly marine and are thought to include numerous obligate parthenogens still, little is known about the distribution, origin and evolution of parthenogens in this group. Reports of geographical parthenogenesis from land and freshwater are numerous, but this occurrence has been rarely reported from the sea. Geographical parthenogenesis, a phenomenon where parthenogens and their close sexual relatives inhabit distinct geographical areas, has been considered an interesting topic in evolutionary biology.

Geographic distance matrix in genodive