Article.Pdf (879.9Kb)
Total Page：16
File Type：pdf, Size：1020Kb
AJB Advance Article published on February 27, 2012, as 10.3732/ajb.1100363. The latest version is at http://www.amjbot.org/cgi/doi/10.3732/ajb.1100363 American Journal of Botany 99(3): 000–000. 2012. F REQUENCY OF LOCAL, REGIONAL, AND LONG-DISTANCE DISPERSAL OF DIPLOID AND TETRAPLOID S AXIFRAGA OPPOSITIFOLIA (SAXIFRAGACEAE) TO 1 ARCTIC GLACIER FORELANDS E IKE M Ü LLER 2,3,5 , PERNILLE BRONKEN E IDESEN 2 , DOROTHEE E HRICH 3 , AND I NGER GREVE A LSOS 2,4 2 The University Centre in Svalbard (UNIS), Post Offi ce Box 156, NO-9171 Longyearbyen, Norway; 3 Department of Arctic and Marine Biology, Faculty of Biosciences, Fisheries and Economics, University of Troms ø , NO-9037 Troms ø , Norway; and 4 Troms ø University Museum, NO-9037 Troms ø , Norway • Premise of the Study: Climate change forces many species to migrate. Empirical small-scale data on migration and colonization in the Arctic are scarce. Retreating glaciers provide new territory for cold-adapted plant species, but the genetic consequences depend on dispersal distances and frequencies. We estimated local, regional, and long-distance dispersal frequencies, as well as their effect on levels of genetic diversity, in diploid and tetraploid individuals of Saxifraga oppositifolia . • Methods: Samples were collected in four aged moraines in each of three glacier forelands, in surrounding areas and reference populations in the Arctic archipelago Svalbard. These samples were analyzed for neutral amplifi ed fragment length polymor- phisms (AFLPs, n = 707) and ploidy levels ( n = 30). • Key Results: Genetic clustering and ploidy analyses revealed two distinct genetic groups representing diploids and tetraploids, with few intermediate triploids. The groups were intermixed in most sampled populations. No differences in genetic diversity were found between tetraploids and diploids, or between established and glacier foreland populations. Seeds were dispersed over local, regional, and long distances, with the highest proportions of seeds originating from close sources. A minimum of 4 – 15 founding individuals from several source populations had initially established in each glacier foreland. • Conclusions: Our data suggest that S. oppositifolia can rapidly colonize new deglaciated areas without losing genetic diversity. Thus, glacier forelands can be alternative habitats for cold-adapted vascular plants tracking their climatic niche. Our data show no difference in colonization success between diploid and tetraploid individuals. Key words: AFLP; Arctic; colonization; dispersal; founder; genetic diversity; glacier forelands; migration; ploidy; Saxifraga oppositifolia . During recent decades, several studies have focused on Arc- evaluate the effect of ongoing climate change on dispersal and tic plant species and their large-scale responses to Pleistocene potential loss of genetic diversity during short-term range shifts range shifts ( Abbott et al., 1995, 2000 ; Eidesen et al., 2007a , b ; in the Arctic. Westergaard et al., 2010 ). These studies clearly show that his- Several colonization models ( Ibrahim et al., 1996 ; Austerlitz torical range shifts have altered the genetic diversity within et al., 1997 ; Bialozyt et al., 2006 ) and empirical studies about several Arctic plant species. Nearly all Arctic species will pre- postglacial colonization ( Hewitt, 1996 ; Sch ö nswetter et al., sumably experience range shifts, or range contractions, in re- 2003 ) suggest that range expansion into formerly glaciated sponse to ongoing climate warming ( Parmesan, 2006). These areas can result in decreased genetic diversity owing to subse- future range shifts may lead to a considerable loss of genetic quent bottlenecks and founder effects. In addition, newly founded diversity over a relatively short period (i.e., centuries; Alsos et al., populations can diverge genetically from source populations unpublished data). Nevertheless, in many Arctic areas, new ter- because of a different selection pressure in the new habitat ritory for colonization is continuously provided in front of re- (McCauley and Wade, 1980). Reduced genetic diversity may treating glaciers. It has been suggested that some Arctic plants have negative effects on factors like adaptation potential, resis- may endure future climate alterations by fi nding adequate habi- tance to disturbance, and stability of a species ( Reusch et al., tats in such formerly glaciated areas ( Crawford, 2008 ). Detailed 2005 ; Hughes et al., 2008 ). Thus, persistence of a species is not studies of small-scale plant migration are therefore needed to guaranteed solely by moving; it also has to have suffi cient ge- netic variation to endure in the long run. However, the modeling studies suggest that genetic diversity in newly founded popula- 1 Manuscript received 23 July 2011; revision accepted 10 January 2012. tions can be high if there is a high proportion of long-distance The authors thank the Troms ø University Museum and K. Bakke dispersal coupled with local diffusion (stratifi ed dispersal) Westergaard for support during the laboratory work. We thank E. J. Cooper, ( Ibrahim et al., 1996 ; Bialozyt et al., 2006 ). This phenomenon S. Lovibond, and two anonymous reviewers for comments that improved has been supported through several large-scale empirical stud- the manuscript. The fi eld work of the project was funded by a personal ies ( Alsos et al., 2005, 2009 ; Skrede et al., 2006 ). Similar pat- stipend to E. M ü ller from the Arctic Field Grant of the Svalbard Science Forum. The remaining costs of the project were funded by the University terns have also been shown in several small-scale colonization Centre in Svalbard. studies, with no founder effects and only minor differences in 5 Author for correspondence (e-mail: [email protected]) genetic diversity between newly founded populations and source populations ( Von Fl ü e et al., 1999 ; Raffl et al., 2006 ; doi:10.3732/ajb.1100363 Yang et al., 2008 ). American Journal of Botany 99(3): 1–13, 2012; http://www.amjbot.org/ © 2012 Botanical Society of America 1 Copyright 2012 by the Botanical Society of America 2 AMERICAN JOURNAL OF BOTANY [Vol. 99 In Svalbard, a High Arctic archipelago, glaciers cover about of local, regional, and long-distance dispersed immigrants; 60% of the land mass; thus, deglaciated areas are continuously and (3) the minimum number of founding individuals con- provided. Several well-documented colonization studies of gla- tributing to the genetic patterns observed in the newly founded cier forelands in Svalbard are already available (Hodkinson populations. et al., 2003 ; Moreau et al., 2005, 2008 ). In addition, this area provides several dated chronosequences ( Dzierzek et al., 1990 ; Sletten et al., 2001 ; Rachlewicz et al., 2007 ). Ecosystems in MATERIALS AND METHODS Svalbard have comparatively simple interactions ( J ó nsd ó ttir, 2005 ) and little anthropogenic disturbance ( Krzyszowska, 1985, 1989 ). Sampling — Leaves of S. oppositifolia were collected in three forelands of Thus, glacier forelands in Svalbard provide an ideal model system the glaciers Midtre Lov è nbreen, Hø rbyebreen, and Renardbreen in Svalbard. Chronosequences of these glacier moraines were reconstructed with aerial im- for investigating genetic effects of ongoing plant colonization. ages from the Norwegian Polar Institute for the years 1936, 1960, and 1990. In Saxifraga oppositifolia L. (Purple Saxifrage) is a long-lived, addition, the chronosequences and the outermost moraine of the “ Little Ice perennial, insect-pollinated, mainly outcrossing herb ( Kevan, Age ” were verifi ed using earlier studies from each of the three moraines 1972 ; Gugerli, 1998 ). This species is an early colonizer, dis- ( Dzierzek et al., 1990 ; Moreau et al., 2005 ; Rachlewicz et al., 2007 ). In each perses via seeds and presumably also via propagules ( Cooper, glacier foreland, one population from each of the four moraine stages as well as 2006 ), and is the fi rst dominant vascular plant in young mo- four populations from surrounding potential sources were collected ( Fig. 1 ) . The four sources in each collection region were chosen with regard to the ease raines after deglaciation ( Hodkinson et al., 2003 ; Raffl et al., of access and to the distance to the glacier foreland. With each successive 2006 ). It has a circumpolar Arctic – Alpine distribution ( Hult é n, source, the distance to the glacier foreland was increased. Therefore, the closest 1986 ) and displays considerable morphological and genetic sources were 0.43 – 1.99 km and the most distant sources 5.25 – 8.42 km away variation throughout its range ( Abbott et al., 2000; Abbott and from the oldest moraine. Leaves were collected from 30 individuals that were Comes, 2004 ; Elven et al., 2011 ). Two subspecies are proposed ≥ 10 m apart. If fewer individuals were present, fewer samples were collected. in the Arctic: the amphi-Beringian subspecies smalliana and To include reference populations, we additionally collected 10 individuals from seven other locations in Svalbard. Thus, in total, 780 samples from 31 popula- the more widely distributed subspecies oppositifolia ( Elven tions were collected in silica gel ( Table 1 ) . One voucher specimen was col- et al., 2011 ). In addition, two distinct morphotypes were de- lected from each collection site ( Table 1 ) and deposited at Tromsø University scribed, one cushion-like type growing mostly in dry, wind- Museum (TROM). exposed ridges, and one prostrate type with long branches and distant leaves mainly found in damp, less exposed