Najas Minor (Hydrocharitaceae) in North America: a Reappraisal
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Aquatic Botany 126 (2015) 60–72 Contents lists available at ScienceDirect Aquatic Botany journal homepage: www.elsevier.com/locate/aquabot Najas minor (Hydrocharitaceae) in North America: A reappraisal a,∗ a,1 a,2 a,3 Donald H. Les , Elena L. Peredo , Nicholas P. Tippery , Lori K. Benoit , a a b,4 b c Hamid Razifard , Ursula M. King , Hye Ryun Na , Hong-Keun Choi , Lei Chen , a,5 d Robynn K. Shannon , Sallie P. Sheldon a Department of Ecology and Evolutionary Biology, University of Connecticut, Storrs, CT 06269-3043, USA b Department of Biological Sciences, Ajou University, Suwon 443-749, Republic of Korea c South China Botanical Garden, Chinese Academy of Sciences, Guangzhou 510650, China d Department of Biology, Middlebury College, Middlebury, VT 05753-6151, USA a r t i c l e i n f o a b s t r a c t Article history: Genetic studies of nonindigenous populations can help to determine their geographical origin, whether Received 19 March 2015 single or multiple introductions have occurred, and provide evidence of hybridization. We broadly sur- Received in revised form 16 June 2015 veyed Najas minor populations at several nuclear and chloroplast loci. Sequence data were obtained from Accepted 23 June 2015 nonindigenous N. minor populations in North America and portions of its native range in Europe (Italy) Available online 29 June 2015 and Asia (China, Korea). North American populations were mapped to evaluate the observed patterns of genetic variation geographically. We detected multiple genotypes of N. minor in collections originating Key words: from within Eurasia and North America. In North America, the presence of two, distinct, widespread Aquatic plant genotypes indicated at least two separate introductions. These genotypes shared partial genetic similar- Genetic variation Hybridization ity with accessions from China. Two other genotypes (restricted to Michigan, Ohio, and West Virginia) Invasive represented either additional introductions of hybrid plants, and/or post-introduction hybrid events that Multiple introduction occurred in North America. The existence of several genotypes among nonindigenous North American Najas oguraensis N. minor populations indicates a history of multiple introductions, and raises concerns over the poten- Nonindigenous tial proliferation of novel hybrid genotypes in this region. Because the two main genotypes essentially Weed remain allopatric, management efforts should focus on preventing their contact, which could result in proliferation of hybrid plants with enhanced invasive attributes. © 2015 Elsevier B.V. All rights reserved. 1. Introduction About 5000 nonindigenous plant species have become natural- ized in North America, many as noxious weeds (Morse et al., 1995). Aquatic habitats are particularly susceptible to plant invasions. Wetlands harbor nearly a fourth of the world’s seriously invasive ∗ Corresponding author. Fax: +1 860 486 6364. species (Zedler and Kercher, 2004) and numerous water bodies E-mail addresses: [email protected] have become infested with nuisance hydrophytes (Pieterse and (D.H. Les), [email protected] (E.L. Peredo), [email protected] (N.P. Tippery), Murphy, 1993). Introduced aquatic plants impact native habitats, lori [email protected] (L.K. Benoit), [email protected] (H. Razifard), [email protected] (U.M. King), [email protected] (H.R. Na), [email protected] interfere with navigation and recreation, and infest agricultural sys- (H.-K. Choi), [email protected] (L. Chen), [email protected] tems that cultivate rice and other water plants (Pimentel et al., (R.K. Shannon), [email protected] (S.P. Sheldon). 1 2001). Such introductions are devastating economically, costing the Present address: The Ecosystems Center, Marine Biological Laboratory, 7 MBL United States over $100 million each year for control programs, and Street, Woods Hole, Massachusetts, 02543, USA. 2 Present address: Department of Biological Sciences, University of Wisconsin- an additional $10 million in related economic losses (Pimentel et al., Whitewater, Whitewater, Wisconsin, 53190, USA. 2001; Lovell et al., 2006). Some estimates have ranked these annual 3 Present address: U.S. Fish and Wildlife Service, 50 Bend Road, Charlestown, losses at $1-10 billion (Rockwell, 2003). Rhode Island, 02813, USA. 4 It is necessary to understand nonindigenous species distri- Present address: Northeastern Asia Plant Institute, Seoul, 135-943, Republic of Korea. butions to evaluate source(s) of introduction (Les et al., 2013), 5 Present address: College of Science and Technology, Fairmont State University, potential for spread in natural communities (Les and Mehrhoff, Fairmont, West Virginia, 26554, USA. http://dx.doi.org/10.1016/j.aquabot.2015.06.005 0304-3770/© 2015 Elsevier B.V. All rights reserved. D.H. Les et al. / Aquatic Botany 126 (2015) 60–72 61 Table 1 1999), and ecological factors pertaining to their place of origin, Earliest North American state or provincial* records of Najas minor based on pub- all which may help to elucidate management strategies (Müller- lished accounts or herbarium records (LSU; CONN). Genotypes determined by this Schärer et al., 2004). It also is important to determine whether study are indicated (n/a = material not evaluated; n/a** = region searched but no multiple introductions occur because such events can confer high material located). adaptive potential to invaders by increasing genetic diversity Locality Year Source This study through intraspecific recombination or interspecific hybridization OH 1932 Wentz and Stuckey (1971) USA-1; nrITS-1/pdsG (Genton et al., 2005; Lavergne and Molofsky, 2007; Culley and NY 1934 Clausen (1936) USA-2 Hardiman, 2009; Schierenbeck and Ellstrand, 2009). Genetic stud- AL 1943 Meriläinen (1968) USA-1 ies of invasive species also help to characterize their competitive TN 1944 Meriläinen (1968) n/a potential (Bossdorf et al., 2005), provide evidence of hybridization WV 1947 Meriläinen (1968) USA-1; nrITS-2/pdsR MI 1949 Wentz and Stuckey (1971) USA-1; nrITS-1/pdsG with native species (Moody and Les, 2002), and clarify taxonomic GA 1951 EDDMapS (2014) USA-1 issues pertaining to submersed plants, whose highly reduced mor- PA 1951 EDDMapS (2014) USA-1 phologies render them prone to misidentification (Les et al., 2006). FL 1958 Meriläinen (1968) USA-1 Najas ranks among the roughly three percent of plants compris- IN 1958 Wentz and Stuckey (1971) USA-1 ing major aquatic weeds worldwide (Sidorkewicj et al., 2004). IL 1963 Meriläinen (1968) USA-1 VT 1965 EDDMapS (2014) USA-2 Najas minor All. was introduced to North America in the early 20th SC 1969 EDDMapS (2014) USA-1 century (Meriläinen, 1968; Wentz and Stuckey, 1971). Although KY 1974 This study (LSU) USA-1 generally not problematic in its native range (where it tends to be MA 1974 EDDMapS (2014) USA-2 rare), N. minor has become widespread in North America where AR 1979 EDDMapS (2014) USA-1 MS 1979 EDDMapS (2014) USA-1 it displaces native plants and interferes with recreational activi- OK 1979 Nelson and Couch (1981) USA-1 ties (Fig. S1). It is listed as a noxious weed in several U.S. states LA 1980 Sullivan (1981) n/a** (USDA, 2012). Its method of introduction is unknown, but has MD 1982 EDDMapS (2014) USA-1 been attributed to escapes from cultivation or waterfowl food plant VA 1985 EDDMapS (2014) USA-1 propagation programs (Les and Mehrhoff, 1999). MO 1990 EDDMapS (2014) USA-1 NH 1992 Padgett and Crow (1993) n/a N. minor is a submersed, water-pollinated, freshwater annual CT 1995 This study (CONN) USA-2 whose historical native distribution once extended throughout NC 1964 Radford et al. (1964) n/a** Eurasia and northern Africa (Triest, 1988). This sexual species dis- IA 1998 EDDMapS (2014) USA-2 perses primarily by seeds, given that asexual reproduction (by ON* 1999 Smith (2003) n/a DE <2000 Haynes (2000) n/a** shoot fragmentation) is inefficient and provides no means of over- MN 2001 EDDMapS (2014) USA-1 wintering. Despite its former presence, occurrences have dwindled CA 2003 Les et al. (2012) USA-2 in Western Europe (Casper and Krausch, 1980), with few additional SD 2006 Larson (2010) n/a 20th century records (Triest, 1988). The species also is endangered KS 2007 Morse et al. (2007) USA-1 in Japan (JIBIS, 2012) and rare in Hong Kong (Yip et al., 2010). Col- WI 2007 Skawinski (2010) USA-2 NJ 2008 EDDMapS (2014) USA-2 lections from rice fields in Azerbaijan, China, Italy, Iran, Japan, and TX 2010 Les et al. (2012) USA-1 Turkey (Triest, 1988) indicate alterations to the original distribu- tion of N. minor by human-mediated dispersal. Consequently, it can anomalies prompted us to reevaluate the current distribution of N. be difficult to determine whether records of N. minor, even within minor in North America in order to clarify the geographical origin its original native range, represent indigenous or non-indigenous of the nonindigenous populations. populations. Contaminated planting stocks also have introduced Najas species to rice fields in Australia and California (McIntyre 2. Methods and Barrett, 1985). California introductions include N. gracillima (A. Braun ex Engelm.) Magnus, N. graminea Delile, and N. minor (Les 2.1. Sampling et al., 2012, 2013). N. minor is distinct taxonomically by its laterally striate seed are- All authors participated in surveying more than 1500 potential oles, a generic feature shared only with N. oguraensis Miki (Triest, Najas habitats in North America or Asia during field work con- 1988). These taxa have been distinguished by their unilocular ducted from 2009 to 2012. About a third of American sites surveyed (N. minor) or quadrilocular (N. oguraensis) anthers (Triest, 1988), contained one or more Najas species (Fig. 1a). We also included sev- although otherwise they are virtually impossible to differentiate eral N. minor specimens (from MA, MN, WI) sent by colleagues or morphologically. Vegetative N. minor material requires genetic sampled with permission from herbarium material (CDA, CONN). analysis for confident identification. In North America, N.