Tenerife), as well as S. gymnomaschala of the southern part of the Moroccan west coast. 3. S. divaricata on the eastern islands (La Graciosa and. Lanzarote).
East meets West Geographic groups of Salsola divaricata (Chenopodiaceae) on the Canary Islands and closely related species in Morocco Delphine Tefarikis1, Helmut Freitag2 & Gudrun Kadereit1 1
Institute für Allgemeine und Spezielle Botanik, Johannes Gutenberg-Universität Mainz, 55099 Mainz, Germany 2 Institut für Biologie - Fachgebiet Botanik, Universität Kassel, 34132 Kassel, Germany
The Canary Islands This volcanic archipelago is located off the coast of North-West Africa and their subtropical climate is influenced by atmospheric and oceanic circulation systems in combination with the islands’ relief [1]. The eastern islands are more arid with higher temperatures in summer and low precipitation compared to the western islands. The wide variety of climatic conditions lead to a high diversity of ecosystems and the characteristic biodiversity with a high level of endemism and radiation [2]. The supposedly endemic shrub Salsola divaricata Moq. (Salsoleae, Chenopodiaceae) is common in coastal and inland habitats on five of the seven main islands and some of the islets. The closest relatives of S. divaricata are Salsola verticillata Schousb., S. deschaseauxiana Litard. & Maire and S. gymnomaschala Maire which can be found along the Atlantic coast of Morocco. These four species are difficult to distinguish by morphology and standard nuclear ribosomal (ITS/ETS) and non-coding chloroplast markers.
A
B Fig. 1: Population structure by Structure v.2.3.4. [3]. A) Structure-plot of the complete data set without outgroup, two clusters. B) Structure-plot of a subset of the data set: Salsola divaricata and S. gymnomaschala, three clusters. Population number above the bars. Geographic origin see Fig. 2.
Does the genetic differentiation of several populations of Salsola divaricata and the three closely related species reflect the geographic origin? Analysis regarding geographic groups To resolve the relationship among 21 populations of the four species of interest a Genotyping-by-Sequencing approach was used. We gained 3463 markers and 12812 SNPs which were then analyzed with Structure v.2.3.4. [3]. This revealed a strong geographic clustering and a number of admixed populations (Fig. 1 and 2). Further analysis with RAxML [4] excluding admixed individuals resulted in a mostly wellsupported tree and three well resolved geographic groups could be identified: Populations of 1. S. verticillata and S. deschaseauxiana of the northern part of the Moroccan west coast 2. S. divaricata on the western islands (La Gomera and Tenerife), as well as S. gymnomaschala of the southern part of the Moroccan west coast 3. S. divaricata on the eastern islands (La Graciosa and Lanzarote). The tree (Fig. 3) also indicates the successive colonization of the Canary Islands from Southwest Morocco. Since especially those populations and individuals located in areas between these groups are admixed, gene flow seems likely. All four species are anemogamous and their winged fruits could be easily dispersed by the trade winds and Saharan sand storms. The results also suggest a re-evaluation of the species concept in this group. Further studies are needed to clarify if the genetic differentiation is due to the different environmental conditions on the eastern and western islands or due to the physical distance. Other traits such as anatomy and biochemistry are currently investigated.
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Fig. 2: Studied populations (written in blue letters = Salsola verticillata (Sv) and S. deschaseauxiana (Sx); green letters = S. gymnomaschala (Sg), orange = S. divaricata (Sd)) and geographic groups according to Structure-analysis (circle colours similar to colours in Fig. 1, asterisks denote admixture, yellow asterisk = admixture between clusters of Fig. 1 A; white asterisk = admixture between clusters of Fig. 1 B). Top left corner: Fruit of S. divaricata (Photo by D. Tefarikis). Morocco west coast North Morocco west coast South
La Gomera & Tenerife Gran Canaria Fuerteventura
La Graciosa & Lanzarote
Fig. 3: RAxML-tree excluding admixed individuals. First indication of colonization from Southwest Morocco. Abbreviations of populations and species as in Fig. 2. Sources: 1. Yanes, Y. et al. (2008) Chemical Geology 249(3-4) ; 377–392, 2. Fernández-Palacios, J. M. & Whittaker, R. J. (2008) J. Biogeogr. 35, 379–387; 3. Pritchard, J. K., Stephens, M. & Donnelly, P. (2000) Genetics 155: 945–959; 4. Stamatakis, A., Hoover, P., Rougemont, J. (2008) Systematic Biology 75: 758–771
