Declining Genetic Diversity and Increasing Genetic Isolation toward the Range Periphery of Stipa pennata, a Eurasian Feather Grass Author(s): Viktoria Wagner, Jan Treiber, Jiři Danihelka, Eszter Ruprecht, Karsten Wesche, and Isabell Hensen Reviewed work(s): Source: International Journal of Plant Sciences, Vol. 173, No. 7 (September 2012), pp. 802-811 Published by: The University of Chicago Press Stable URL: http://www.jstor.org/stable/10.1086/666663 . Accessed: 19/09/2012 15:37 Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at . http://www.jstor.org/page/info/about/policies/terms.jsp . JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact [email protected]. The University of Chicago Press is collaborating with JSTOR to digitize, preserve and extend access to International Journal of Plant Sciences. http://www.jstor.org Int. J. Plant Sci. 173(7):802–811. 2012. Ó 2012 by The University of Chicago. All rights reserved. 1058-5893/2012/17307-0006$15.00 DOI: 10.1086/666663 DECLINING GENETIC DIVERSITY AND INCREASING GENETIC ISOLATION TOWARD THE RANGE PERIPHERY OF STIPA PENNATA, A EURASIAN FEATHER GRASS Viktoria Wagner,1,* Jan Treiber,y Jirˇi Danihelka,z Eszter Ruprecht,§ Karsten Wesche,y and Isabell Hensen* *Institute of Biology/Geobotany and Botanical Garden, Martin Luther University Halle-Wittenberg, Am Kirchtor 1, D-06108 Halle, Germany; ySenckenberg Museum of Natural History, Go¨rlitz, P.O. Box 300 154, D-02806 Go¨rlitz, Germany; zDepartment of Vegetation Ecology, Institute of Botany, Academy of Sciences of the Czech Republic, Lidicka´ 25/27, CZ-60200 Brno, Czech Republic, and Department of Botany and Zoology, Faculty of Science, Masaryk University, Kotla´rˇska´ 2, CZ-61137 Brno, Czech Republic; and §Hungarian Department of Biology and Ecology, Babesx-Bolyai University, Str. Republicii 42, RO-400015 Cluj Napoca, Romania A common assumption in ecology and evolutionary biology is that genetic diversity declines and differentiation increases toward the edge of a species’ geographic range, where populations tend to be smaller and more isolated. We tested these predictions in a characteristic Eurasian steppe plant, Stipa pennata,by inspecting 230 AFLP bands in 26 populations (345 individuals) along a 3300-km longitudinal gradient from the range core, in Russia, to the range periphery, in central Europe. Overall, our study species showed low genetic diversity within populations (mean proportion of polymorphic bands ¼ 21:2%) and moderately high genetic differentiation among them (mean FST ¼ 0:29). As predicted, genetic diversity declined significantly from the range core to the periphery but was not correlated with population size. Pairwise genetic dif- ferentiation was significantly higher among peripheral populations than central populations but did not show a pronounced relationship with geographic distance. Our results indicate that peripheral populations may experience higher genetic drift and lower gene flow than their central counterparts, possibly because of smaller population sizes, spatial isolation, and a more complex landscape structure. In addition, historic range fluctuations and the mixed breeding system could have enhanced the observed patterns in our study species. Keywords: abundant-center model, AFLP, fragmentation, geographic distribution range, range center. Online enhancements: appendix tables. Introduction at the range edge could lead to bottleneck events and, conse- quently, to decreased genetic diversity and increased genetic Genetic variation forms the basis for evolutionary pro- differentiation (Hewitt 1996; Hampe and Petit 2005). cesses and shapes a species’ adaptive potential and popula- Although the hypothesis of lower genetic diversity and tion viability (Reed and Frankham 2003; Boulding 2008). It higher genetic differentiation at the range edge has been sup- is commonly assumed that genetic variation is not evenly ported by theoretical considerations, it has received only distributed across a species’ geographic distribution range: mixed empirical support in the past (Eckert et al. 2008; Har- at the range edge, genetic diversity is expected to be smaller die and Hutchings 2010). Results that diverge from expecta- and genetic differentiation higher than in the range core tions have been explained by the fact that species do not (Hoffmann and Blows 1994; Eckert et al. 2008; Hardie and show an abundant-center distribution to begin with (Yaki- Hutchings 2010). Such a pattern could arise as a consequence mowski and Eckert 2008). Indeed, it has been pointed out of an abundant-center distribution, in which population size that the abundant-center model does not apply to a variety and abundance decline toward the range periphery because of organisms (Sagarin and Gaines 2002). However, even if of unfavorable environmental conditions and/or interactions species naturally show an abundant-center distribution, an- with new competitors, pathogens, or parasites at the range thropogenic fragmentation in the range core could increase edge (Brown 1984; Lawton 1993; Gaston 2009). The decline genetic drift, inbreeding, and genetic isolation among popula- in population size and stronger spatial isolation should in tions and distort the expected pattern. Meanwhile, biological turn lead to inbreeding, high genetic drift, and hampered traits, such as a species’ longevity and ability for long-distance gene flow (Ellstrand and Elam 1993; Vucetich and Waite dispersal, could counteract diversity loss and dampen genetic 2003). Furthermore, repeating expansions and contractions differentiation. We tested the hypothesis of decreasing genetic diversity 1 Author for correspondence; current address: College of Forestry and increasing genetic differentiation toward the range edge and Conservation, University of Montana, Missoula, Montana 59812, in Stipa pennata, one of the most characteristic plants of the U.S.A.; e-mail: [email protected]. western Eurasian steppes (Lavrenko 1970; Nosova 1973). Manuscript received December 2011; revised manuscript received April 2012. Dry grassland plants have received considerable attention by 802 WAGNER ET AL.—GENETIC DIVERSITY AND ISOLATION IN STIPA PENNATA 803 population geneticists in the past, given that many of these is not known. Caryopses are enclosed in the lemma and are plants are red-listed in Europe, including Anthericum liliago dispersed by wind or in animal fur. (Peterson et al. 2008), Astragalus exscapus (Becker 2003), Stipa pennata is native to the temperate zone of Europe and Iris aphylla (Wro´ blewska and Brzosko 2006), Silene chloran- Asia (fig. 1). In its geographic range core, at ;50°–55° latitude tha (Lauterbach et al. 2011), Silene otites (Lauterbach et al. in Russia (fig. 1), it grows in steppes, meadow steppes, and 2012), and Stipa capillata (Hensen et al. 2010). However, forest steppes (Nosova 1973). Steppes occur naturally in this few studies covered large areas across the species’ distribu- region (Adams and Faure 1997), but nomadic tribes have ex- tion range (but see Bylebyl et al. 2008; Wro´ blewska 2008). tended the steppe area since the Eneolithic Age by logging ad- Many dry grassland plants occur at the edge of their distribu- jacent forests, mowing, and livestock grazing (Chibilyov 2002; tion in central Europe but are more frequent in the steppes of Sarychev 2003). In the Middle Ages, when Slavic settlers intro- eastern Europe and Asia. Only one study has used a Eurasian duced agriculture in the region, steppes still covered vast areas dry grassland plant to directly compare genetic variation in (Sarychev 2003). It is only since the eighteenth century that the range core and periphery (Wagner et al. 2011, for S. ploughing resulted in a massive decline of steppe vegetation capillata). The categorical sampling scheme of this study has (Chibilyov 2002; Boonman and Mikhalev 2005). Given the been favored by the majority of other population genetic dramatic habitat loss, S. pennata and many other steppe spe- studies because of its cost-effectiveness and logistic feasibility cies are today red-listed even in their distribution core in Rus- (Eckert et al. 2008). However, it did not allow for broader sia (Golovanov 1988). generalizations beyond the two regions that were compared. At its western geographic periphery, in central Europe, S. To obtain more comprehensive results, we used a continuous pennata is confined to small dry grassland fragments that are sampling scheme across the distribution range of S. pennata, embedded in a matrix of forests, arable fields, and settlements. spanning a 3300-km longitudinal gradient from the geographic Steppe communities used to be naturally distributed during the range core in Russia to the range periphery in central Europe. late Pleistocene in Slovakia and the Czech Republic (Jankov- We expected genetic diversity to be higher and genetic differen- ska´ and Pokorny´ 2008). Macrofossils of S. pennata s. lat. have tiation lower toward the range core in Russia, where the spe- been found as early as from the Holocene, but populations cies has historically been widely distributed. However, recent may have been subject to oscillations in the following millen- transformation of steppe habitats in Russia has resulted in in- nia