Botanica Marina 2019; 62(1): 75–82 Petra Nowak* and Hendrik Schubert Genetic variability of charophyte algae in the Baltic Sea area https://doi.org/10.1515/bot-2018-0021 Received 1 March, 2018; accepted 13 December, 2018; online first 7 January, 2019 Abstract: The Baltic Sea, a young habitat in geological terms, is characterised by strong climatic and salinity gradients that determine species distribution and trigger adaptation processes. The aim here was to test the hypoth- esis that Baltic Sea charophytes which originate from large freshwater populations exhibit a higher genetic vari- ability than euryhaline charophyte species, restricted to a small number of brackish-marine populations. For this, genetic variability of euryhaline, mesohaline and halotol- erant freshwater charophytes with different distribution patterns and population sizes were analysed. Euryha- line Lamprothamnium papulosum, restricted to a few and small populations in the Baltic Sea, showed a complete lack of genetic variability. Also euryhaline Tolypella with large and widely distributed populations displayed only low genetic variability. On the other hand, mesohaline Chara canescens, one of the most common charophytes in the Baltic Sea, exhibited comparatively high genetic variability, in spite of its parthenogenetic mode of repro- duction. Halotolerant Chara baltica, originating from freshwater ancestors with a huge number of populations all over Europe, showed a rather restricted genetic vari- ability, indicating a habitat filter acting prior to colonisa- tion of brackish habitats. Keywords: Chara; genetic diversity; Lamprothamnium; salinity; Tolypella. Introduction The Baltic Sea is regarded as a young ecosystem, whose post-glacial history included freshwater as well as marine periods as a result of land uplift, subsidence effects and sea level changes (Björck 1995). The recent low-saline “Mya Period” started only approximately 1500 years ago (Schiewer 2008), causing again a shift in environmental conditions leading to considerable changes in species composition. Since speciation is a long-term process most of the recent species inventory entered the Baltic Sea from adjacent areas; the resulting species distribution pattern was reviewed by Telesh et al. (2013), including the results for macroalgae (Schubert et al. 2011). The macroalgal flora of the Baltic Sea is mainly recruited from the North Atlantic, with only few locally evolved taxa (e.g. Reinke 1889, Lakowitz 1929, Lüning 1985). Johannesson and André (2006) convincingly proved that dispersal events from the North Atlantic towards the Baltic Sea result in a loss of genetic diversity of marine organisms. As a result, local Baltic forms or varieties of Atlantic macroalgal species are common (e.g. Ceramium tenuicorne, Gabrielsen et al. 2002), but only few of them are accepted as endemic species such as Fucus radicans (Pereyra et al. 2009). Whereas marine immigrants must pass the Kattegat and Belt Sea, significantly restricting the area of origin, freshwater species can immigrate into the Baltic from different locations along the pronounced climatic gradi- ent of the Baltic Sea. As a result, loss of genetic diversity should be less pronounced, because various genotypes, already adapted to the respective climatic conditions, act as founder populations. For angiosperms, Nies and Reusch (2005) have shown a lower genetic diversity of Stuckenia pectinata populations in the Baltic Sea compared to freshwater lakes. However, having evolved from terrestrial relatives, vascular plants had to develop several adaptation mech- anisms to cope with the challenges of aquatic conditions (Du and Wang 2016). In contrast, charophyte algae are phylogenetically old, primary aquatic plants that have a long history of brackish-water colonisation (Schudack 2016). For Chara baltica, AFLP (Amplified Fragment Length Polymorphism) analyses revealed a genetic continuum towards its freshwater counterpart Chara papillosa (syn. Chara intermedia, see Schubert et al. 2016) along a Euro- pean north-south gradient (Boegle et al. 2010b). Nowak et al. (2016) revealed the existence of haplotypes specific to either freshwater species Chara hispida and C. papillosa or brackish water species C. baltica and Chara horrida, indicating a salinity-specific adaptation. *Corresponding author: Petra Nowak, University of Rostock, Aquatic Ecology, Albert-Einstein Str. 3, Rostock 18051, Germany, e-mail: petra.nowak@uni-rostock.de Hendrik Schubert: University of Rostock, Aquatic Ecology, Albert-Einstein Str. 3, Rostock 18051, Germany Brought to you by | Iowa State University Authenticated Download Date | 2/1/19 3:33 PM