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Genetic Diversity and Population Structure of Sickleweed (Falcaria Vulgaris; Apiaceae) in the Upper Midwest USA

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Genetic Diversity and Population Structure of Sickleweed (Falcaria Vulgaris; Apiaceae) in the Upper Midwest USA Biol Invasions DOI 10.1007/s10530-014-0651-z ORIGINAL PAPER Genetic diversity and population structure of sickleweed (Falcaria vulgaris; Apiaceae) in the upper Midwest USA Sarbottam Piya • Madhav P. Nepal • Jack L. Butler • Gary E. Larson • Achal Neupane Received: 31 May 2013 / Accepted: 3 February 2014 Ó Springer International Publishing Switzerland 2014 Abstract Sickleweed (Falcaria vulgaris), an intro- sickleweed in the upper Midwest. Some individuals duced species native to Europe and Asia, grows as an exhibited more than two alleles at several microsatel- aggressive weed in some areas of the upper Midwest in lite loci suggesting occurrence of polyploidy, which the United States. We are reporting genetic diversity could be a post-introduction development to mitigate and population structure of sickleweed populations the inbreeding effects. High genetic variation in the using microsatellite markers and nuclear and chloro- introduced range attributable to multiple introductions plast DNA sequences. Populations showed high and polyploidy may be inducing the evolution of genetic differentiation but did not show significant invasiveness in sickleweed. Results of this study geographic structure, suggesting random establish- provide valuable insights into the evolution of sickle- ment of different genotypes at different sites was likely weed and baseline data for designing proper manage- due to human mediated multiple introductions. Three ment practices for controlling sickleweed in the United genetic clusters revealed by microsatellite data and States. presence of six chlorotypes supported our hypothesis of multiple introductions. Chloroplast DNA sequence Keywords Chlorotypes Á Falcaria vulgaris Á data revealed six chlorotypes nested into two main Microsatellite Á Polyploidy Á trnL-trnF Á trnQ- lineages suggesting at least two introductions of rps16 Electronic supplementary material The online version of Introduction this article (doi:10.1007/s10530-014-0651-z) contains supple- mentary material, which is available to authorized users. Introduced species can have severe repercussions on S. Piya Á M. P. Nepal (&) Á A. Neupane global biodiversity (Sala et al. 2000; Lee 2002; Provan Department of Biology and Microbiology, South Dakota et al. 2005; Lachmuth et al. 2010; Alyokhin 2011); State University, Brookings, SD 57007, USA therefore, it is necessary to be vigilant about every e-mail: [email protected] plant species introduced outside of its range (Simberl- J. L. Butler off et al. 2011). Increasing international commerce has Rocky Mountain Research Station, USDA Forest Service, facilitated tremendous exchange of biotas (Mooney Rapid City, SD 57702, USA and Cleland 2001), a phenomenon expected to facil- itate the spread of introduced species (Frankham G. E. Larson Department of Natural Resource Management, South 2005). Control of an introduced plant species can be a Dakota State University, Brookings, SD 57007, USA daunting task when the species is already invasive, but 123 S. Piya et al. timely identification can ward off major ecological Most studies are focused on the invasive plants with and economic impacts. It is thus essential to identify severe impacts (Pysek et al. 2008), and our knowledge introduced plants that can become invasive as early as of potentially invasive naturalized plants in the lag possible (Kolar and Lodge 2001) so that proper phase of establishment is very limited (Kowarik management can be instituted prior to their establish- 2005). Recently naturalized plants need to be studied ment and spread. Knowledge of the genetic structure to determine their potential for invasion and to and gene flow between founding populations is develop management strategies (Wilson et al. 2011). important to assess the long term persistence of an In this study, we report on the population genetic invading species (Nater et al. 2013). structure of sickleweed (Falcaria vulgaris Bernh.; Conservation biology theory suggests that a popu- Apiaceae) of the upper Midwest in the United States. lation with low genetic diversity tends to undergo Sickleweed is native to southern and central Europe extinction due to genetic drift and inbreeding depres- and extends eastward through Central Asia and the sion (Ellstrand and Elam 1993; Young et al. 1996); Middle East. It is introduced in Africa, northern however, there exists a genetic paradox for invasive Europe, and North and South America (DAISIE 2008; species (Allendorf and Lundquist 2003). Introduced Larina 2008). It has been reported in sixteen states in species that represent a subset of their source popula- the USA (USDA, NRCS 2011) and exhibits disjunct tions usually have reduced genetic diversity compared distribution in the Midwestern, Southern and Eastern to the source population, but they may be capable of regions. It has been reported to occur abundantly in expanding their range in the novel habitat by outcom- three states in the upper Midwest that include Iowa, peting and replacing locally adapted native species Nebraska and South Dakota (Piya et al. 2012). In (Allendorf and Lundquist 2003). A major obstacle for South Dakota, Fort Pierre National Grassland (FPNG) establishment of introduced species in the new range is and Buffalo Gap National Grassland (BGNG) are the to overcome negative effects of small population size two grasslands where this plant has expanded in and low genetic diversity (Leung et al. 2004; Taylor distribution and abundance (Korman 2011). A recent and Hastings 2005). Multiple introductions (Lavergne study by Butler and Wacker (2013) indicates that and Molofsky 2007), a large number of founder human disturbances created gaps in ground cover and individuals (Allendorf and Lundquist 2003), gene flow altered competitive relationships among native spe- among populations (Slatkin 1987) and polyploidy cies, which facilitated the spread of sickleweed at (Comai 2005) are some mechanisms whereby invasive FPNG. We also observed several large populations of species can offset the negative consequences of small sickleweed along roadsides in Nebraska where the population size and reduced genetic diversity. Nebraska Invasive Species Council has listed it as a High genetic diversity and gene flow among popula- potentially invasive plant (NISC 2011). The plant also tions may promote successful spread of an established occurs as much smaller populations in Onawa, Iowa population (Sakai et al. 2001). Higher intra-specific and Brookings, South Dakota. genetic diversity provides greater opportunities for the While sickleweed is abundantly found in some creation of adapted genotypes through genetic reshuffling states of the Midwest, there are no recent reports of the and recombination, and also more options for natural species in the eastern USA (Piya et al. 2012). Several selection of genotypes better suited for the environment introduced populations may fail at different stages of thus producing a population better able to exploit the invasion and may disappear (Richardson et al. 2000). novel conditions of the introduced range (Lavergne and This may have been the fate of sickleweed introduced Molofsky 2007). Therefore, investigation of genetic in the eastern USA. It is also plausible that the plant diversity and population structure and determination of may occur in this region but its frequency is so low that number of introductions in the novel range can provide a the plant has become inconspicuous. In Iowa, strong framework for assessing invasiveness (Sakai et al. Nebraska and South Dakota, however, some popula- 2001; Valliant et al. 2007). At the same time, such studies tions have naturalized and are expanding. Therefore, may identify source populations (Novak and Mack 2001; in this study, we have included populations from these Genton et al. 2005;Provanetal.2005; Valliant et al. three states. Butler and Wacker (2013) reviewed that 2007) and help design effective control measures for an many naturalized associates of sickleweed from invasive species (Sakai et al. 2001). Eurasia have successfully established in similar 123 Genetic diversity and population structure Fig. 1 Chlorotype variation in F. vulgaris. a Distribution map of chlorotypes in Iowa, Nebraska and South Dakota and b Chlorotype network. Each chlorotype is represented by a circle size proportional to the relative frequency of the chlorotype habitats in North America and indicated that sickle- both chloroplast and nuclear DNA markers to achieve weed might therefore be pre-adapted to the environ- the following objectives: (1) study the genetic diver- mental conditions of Great Plains. The current sity and structure of upper Midwest populations of sickleweed distribution pattern perhaps signifies the sickleweed in the United States, and (2) determine importance of species introductions at multiple sites whether sickleweed populations in the United States with different conditions, whereby some populations were established from a single introduction or resulted overcome all barriers in the introduction-naturaliza- from multiple introductions. tion-invasion continuum (Lockwood et al. 2005; Simberloff 2009; Blackburn et al. 2011). Sickleweed is described as annual, biennial or Methods perennial (Clapham et al. 1987; Korman 2011). It produces protandrous andromonoecious flowers Sample collection (Knuth 1908) and large numbers of seeds. The plant exhibits a characteristic seed dispersal mechanism: A total of 96 samples from eight populations were when the plant senesces, the stems break at the nodes collected
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