genetic variation among north american populations ofphragmites australis: implications for...

Estuaries Vol. 26, No. 2B, p. 444-451 April 2003

Genetic Variation among North American Populations of

Phragmites australis: Implications for Management

KRISTIN SALTONSTALL*

D@artme~zt of Ecolog 7 and Evoh~dona U Bioiow, }~de UtdversiO~, P.O. Box 208106, Ne~ Havete, Co~t~tecticut~ 06520-8106

ABSTRACT: Over the past century, the distribution and abundance o f Phragmites augtralis ( common reed) has dramatically increased in both freshwater and brackish wetlands throughout North America. It has been hypothesized that the increased competitive ability of Phragmites could be the result of an introduction of a more aggressive genotype. Sequence data from 2 noncoding regions of the dlloroplast genome show that, historically, 11 native haplotypes were fmmd across North America and population-structuring distinguishing samples from the Atlantic Coast, Midwest, West, and Gulf Coast regions of the continent was evident. Today a single genetically-distinct haplotype dominates the Atlantic Coast and is also found across the continent in lower frequencies; this type is common in Europe and Asia and has most likely been introduced to North America. Comparisons of modern populations with historic samples show that, along the Atlantic Coast, this cosmopol i tan type has replaced native haplotypes and it is invading new sites throughout the rest of tile country, hi the Mklwest and West, native populations are still co lnmon but introduced populat ions are found along roadsides throughout the area. Gulf Coast populations are dominated by" another populatiml type that is genetically distinct from all other North American population types.

In t roduc t ion

The Nor th Amer ican distr ibution and abundance of 1)h~¢~mites a,~st~dis (Car.) Trin cx Steudcl (hereaf ter P/~raKmi~es ) has increased dramatically over the past 150 years. While the historical record indicates quite clearly that Phre~mi~es is natiw~ to the con t inen t (Niering et al. 1977; I I ansen 1978; Orson 1999; G o m a n and Wells 2000), this spread has been a t t r ibuted to a variety of causes that in- c lude both h u m a n dis turbance of die landscape (Roman et al. 1984; Marks et al. 1994; Bermess et al. 2002) and in t roduct ion of novel genet ic lineages (Saltonstall 2002). ~Allile the impacts of this invasion arc the subject o f m u c h research and discussion, it is clear that the es tabl i shment of I)hrag - mites m o n o c u l t n r e decreases the biodiversity of Nor th ~4anerican wetlands (Chambers et al. 19{)9; Meycrson et al. 2000) and, once present , it is nearly impossible to eradicate (Marks et al. 1994).

Use of DNA sequence data in popu la t ion genet ic studies of plants has been h a m p e r e d b v a lack of variable genetic markers . A n u m b e r of n o n c o d i n g chloroplas t DNA regions that show intraspecific variability have r e c e n @ been identif ied (Taberle t et al. 1991; Hami l ton 1999; Saltonstall 2001), and their use in analyzing popu la t ion level processes is b e c o m i n g m o r e widespread (McCaulcy 1995; P o w -

* Current address: ttorn Point Laboratory, Universib, of Maryland Center for Environmental Science, RO. Box 775, Cambridge, Maryland 21613; tele: 410/221-8478; fax: 410/22]- 8490; e-mail: kristin'salt°nstall@aya'yale'edu"

ell et al. 1995; Dumol in -Lapeque et al. 1997). Chlo- roplast DNA is maternal ly inher i ted in angio- sperms and disperses in seeds but not pollen. It is highly conserved and has been shown to displav spatial s t ructur ing within species, such that the ma- jority of genet ic variat ion is dis t r ibuted a m o n g geographic popula t ions r a the r than within them (Sol- tis et al. 1997; Ohsako and Ohnishi 2000). Each chloroplas t haplo type represen ts a l ineage that is inher i ted maternal ly and is ma in ta ined in a populat ion b v dispersal of seed or vegetative fl'ag- Inents.

A n m n b e r of studies have suggested that levels of genet ic variat ion in Phrag~zites are high. Karyo- typic studies have shown a wide range of ploidy levels within the species t h r o u g h o u t the world with mixed cytotype popula t ions found in several places (reviewed in Clevering and Lissner 1999; Cham- bers et al. 1999). Polvmerase chain react ion (PCR)- based studies have also ffonnd high levels of diversity at the popu la t ion level in bo th Europe and Nor th kaner ica (Djebromli 19{}2; Zcidler et al. 1994; Koppitz et al. 1997; Koppitz 1999; Keller 2000). Pellegrin and H a u b e r (1999) found high levels of variat ion in Midwestern and Atlantic Coast popula t ions of Phragmites in the Uni ted States using isozvmes. Al though the molecu la r techniques used in these studies typically reveal m o r e r andom- ly amplif ied po lymorph ic DNAs ( ~ ) D s ) or less r e s t r i c t i o n ti~aglnent l e n g t h p o l y m o r p h i s m s (RFLPs, i sozymes) gene t i c diversity, Sal tonsta l l (2002) also found that genet ic l ineages were geo-

© 2003 Estuanne Research Federation 444

graphically structured worldwide based on se- quenc ing of' chloroplast DNA. Haplotypes, or lineages, t ound in Europe were distinct fl~om those native to Nor th America and strong evidence for the in t roduct ion of a Eurasian lineage was presented to explain tile rapid spread of tile species in Nor th America.

Today, Phmgmites is typically regarded as an un- desirable species in Nor th America and manage- m c n t actions against it have been widespread. Con- trol techniques commonly used include applica, tion of herbicide, control led burns, water flow ma- nipulations, and mowing (Roman et al. 1984; Marks et al. 1994). Since little has been known re- garding the native status of difIerent Phragmil, es populat ions such actions have been indiscriminate and may, in some cases, have targeted native populations. This analysis presents a detailed picture of file genetic diversity ffmnd in Nor th American Phra~nites populat ions both today and historicMly and assesses tile extent to which in t roduced ge- notypes have become regionally important . Such informat ion is of' great impor tance when deciding an a p p r o p r i a t e m a n a g e m e n t s t ra tegy for sites where PhraKmites is present, particularly in cases where preserw~tion of natiw~ biodiversity is a management goal.

Materials and M e t h o d s

I~eaf tissue samples were obtained fl'om Ph~Y(g'- mites clones t h roughou t its present day and historic ranges across Nor th America. Modern samples were dried in silica gel and frozen upon receipt in the laboratory: Herbar ium specimens, dating back to the 1850s, were kept dry at room temperature. M1 DNA extractions were done using a hexadecyl- t r imethylammonium bromide (CTAJg) extraction protocol (Doyle and Dickson 1987). A total of 206 samples collected f rom m o d e r n populat ions and 141 herbar imn samples, dating fl 'om 1852 to 1974, were analyzed. Two noncod ing chloroplast gene regions, tr**T(UGU)-tr~d~(U~%¢)5' (Taberlet et al. 1991) and ,bcI@sd (SMtonstall 2001) were PCR- amplified and sequenced on an ABI 07 t automatic sequence~; as described in Saltonstall (2002).

Sequences were aligned by eye using Sequench- er 4.21 (GencCodes) and inser t ion /de le t ion (in- del) mutat ions were coded as single base characters to treat them as units ra ther than as mtfitiple character changes. Gaps were treated as a fifth character state. Data t-ore the 2-gene regions were combined to assign haplotype designations and a network was constructed using the statistical par- simony algorithm of Templeton and colleagues (Templeton et al. 1992; Clement et al. 2000). When till sequences were not obtained, samples were assigned to tile most likely haplotype based

Genetic Variation in North American Phragmites 445

~ j ~ ~ Haplotype <> A +=B e=C ~ =A =E =D

, *=F o=G ~]=H [] =1 o=S #=Z • =AA

Fig. 1. Distr ibut ion of all native and GuK Coast Phrag~mi&s haplotypes across Nor th America. Samples inc lude both historic and m o d e r n popula t ion s (1852-2001 ). Mode rn popula t ions dis- playing native haplotypes are p r e s u m e d to have ei ther been present tbr long per iods of" t ime or to r ep resen t recent ly established native popula t ions tha t have dispersed into new sites (Lynch and SaltonstaH 2002).

on the available sequence and geographic location. Calculations of pairwise Fsr values, gene diversity, Analysis of Molecular Variance (AMOVA) analysis, and an exact test of popula t ion dift)rentiat ion (Raymond and Rousset 1995) were pe r fo rmed using Arlequin 2.000 (Schneider et al. 2000). ~M1 sta, tistical analyses were pe r fo rmed on the combined data set.

Resul t s

The data presented here are analyzed under 2 scenarios: a discussion of tile distribution of all native and Gulf Coast lineages found historically across Nor th America, regardless of tile year in Milch samples were collected, and a discussion of tile m o d e r n distribution of these and other nonnative lineages that describes the North American _[)]lF(g~rl?lit~s c o l n l r l u n i t y i n i t s present-day form.

NATIVE AND GUI ,F COAST POPUI,ATIONS

Eleven haplotypes (haplotypes A-H, S, Z, iL"\) were ffmnd in Nor th America that are mfique to the c o n t i n e n t and c o n s i d e r e d to be nat ive (Gcngank Accession Nos. AY016325, AY016327, AY016328, AY016332-AY016335, AF457384, AF457391, AF457392, AF457395-99 , AF457402; Saltonstall 2002). These 11 are distinguished f rom all o ther haplotypes found worldwide by 5 unique mutat ions shared by all. Figure I shows tile distribution of all native haplotypes found ill this stud}, both historically and at present, and depicts the geographic diversity of native Nor th American Phra~dte.s. Haplotype E is the most c o m m o n native type and has a widespread distribution across the

446 K. SaRonstall

B

Fig. 2. Statistical pa rs imony network of 14 Pbragmite.~ hap]o- types t o tmd in Nor th America. Each l ink be /ween haploTypes represents one muta t iona l difference, fl~llowing coding o f inde l s as single characters. Un]abel led nodes indicate in fe r red steps no t foun('l ill the samp]ed popu]ations. Loops in the network are the restflt of homoplas ies in the n u m b e r of repeats in some indels. The ancestral haplotype, or root of the network, is in- d icated by a square. The size of th e oval or square cor responds with the f requency of native haplotypes. Haplotypes are coded accord ing to the geograph ic reg ion in which they are tbund: = Atlant ic Coast, ~ = Midwest-Southern Canada, ~ = West, = Gulf Coast, [ ] = n(mnative.

n o r t h e r n U.S. a nd s o u t h e r n Canada ; it was also c o m m o n historically in New England .

T h e 11 natiw~" hap lo types display s t rong gene t i c s t ruc tu r ing be tween 3 b road ly -de f ined g e o g r a p h i c regions: the Atlantic Coast (Cape C o d s o m h to Georg ia ) , Midwest (Grea t I ,akes reg ion a nd south- e rn Canada ) , a nd ~West (Pacific N o r t h w e s t a n d Sou thwes te rn U.S.; Fig. 2). Pairwise c o m p a r i s o n s o f Fs r values be tween tl~ese reg ions r a n g e d f rom 0.11-0.26, ind ica t ing m o d e r a t e to h igh s t ruc tu r ing be tween p o p u l a t i o n s (Table 1). G e n e diversity (Nci 1987) in these areas was 0.54 _+ 0.05, 0.47 _+ 0.08, and 0.82 _+ 0.03, respectively, wittl the h ighes t levels f o u n d in the West. T h e exact: test o f p o p u - la t ion d i f fe ren t ia t ion also showed signif icant dif- f e ren t i a t ion (p < 0.001) be tween these g e o g r a p h i c regions .

Historically, 4 native hap lo types were f o u n d in the Atlant ic Coast r eg ion o f the U.S., o f wh ich haplotypes E and F were tl~e m o s t c o m m o n regional ly (88% o f samples co l lec ted be fo re 1910). Hap lo - b~pe :'D\ was res t r ic ted to s o u t h e r n New E n g l a n d

'tABLE 1. Pairwise Fs~ values by geographic region of all native and Gulf Coast popl.dations (below diagonal) and all Modern populations, including native, normative, and Gulf Coast populations (above diagonal)..MI populations are significantly dit: fErent at p < 0.05.

Atlantic GuN Coast MidwesL West Coast

Atlantic Coast 0 0.41 0.49 0.78 Midwest 0.1 I 0 0. I B 0.38 West 0.96 0.96 0 0.94 Gulf Coast 0.67 0.70 0.50 0

( C o n n e c t i c u t s h o r e l i n e ) a n d h a p l o t y p e Z was t b n n d in a single m o d e r n sample f l 'om Mary land . These 2 hap lo types share b o t h a single basepa i r (bp) subst i tu t ion and an inde l m u t a t i o n in the tr~tT-t,rnL r eg ion with h a p l o t y p e F (Fig. 2), a n d to- g e t h e r the 3 f o r m a g r o u p whose d is t r ibu t ion appears to be res t r ic ted to the Atlantic Coast reg ion .

I I a p l o ~ p e E is the m o s t c o m m o n ~ p e t h r o u g h - ou t the Midwest a n d s o u t h e r n C a n a d a a n d was f o u n d across the r eg ion (Fig. 1). ~adso p r e s e n t in lower f l-equencies were hap lo types S and G tha t were n o t f o u n d in the Atlant ic Coas t o r West g r o u p s bu t were f o u n d in Nova Scotia and New Brunswick. These 3 hap lo types are also closely re- la ted bu t do n o t share any u n i q u e m u t a t i o n s (Fig. 2).

H a p l o ~ p e s A, C, D, a n d H are res t r ic ted to west- e rn N o r t h Amer i ca ( 'Washington, O r e g o n , Idaho , M o n t a n a , \ ; ~ o m i n g , California, Nevada, Utah, Ar- izona, New Mexico) . H a p l o ~ p e B is also p reva len t in this area bu t its d i s t r ibu t ion ex tends east to Kan- sas and O k l a h o m a . These 5 hap lo types are closely re la ted (Fig. 2) a n d hap lo types A - D share a 31 bp inde l in the rbcL-psM r eg ion tha t is n o t f o u n d in h a p l o t y p e H or any o f the o t h e r native haplo types . H a p l o t y p e E was also f b u n d in W a s h i n g t o n , O r e g o n , Wyoming , and s o u t h e r n British Colum- bia, bu t does n o t a p p e a r to e x t e n d its r a n g e in to the Southwest .

A single ~ p e , h a p l o ~ p e I, is d o m i n a n t across the Gul f Coast a n d in to Mexico (Fig. 1 ). I t also ex t ends west in to the Gul f o f Cal i fornia and sou th to nor f l> e rn par ts o f Sou th Amer ica . t I a p l o ~ p e I is qui te dist inct f>om the 11 native N o r t h A m e r i c a n types and shares n o n e o f the m u t a t i o n s tha t l ink t h e m (Fig. 2). Pairwise c o m p a r i s o n s o f FsT values between the Gul f Coas t and o t h e r g e o g r a p h i c r eg ions r a n g e d fl~om 0 .50-0 .70 ind ica t ing tha t the Gul f Coast r eg ion is s t rongly d i f fe ren t ia ted fl-om all other m'eas o f N o r t h Amer i ca (Table 1).

MODERN POPULATIONS

While native haplob~pes are still p r e sen t today across m u c h o f N o r d l Amer ica , an i n t r o d u c e d lineage, haplob~pe M, has es tabl ished a n d b e c o m e

Haplotype o = A + = B 8 = C x = D / " = E >k=F 0=G I~=H 13=1 o = S "o=Z O = M @=L

Fig. 3. Distribution of all modern l°k~ztg'mites haplotypes collected since 1960 across North America. Black dots indicate tile nonnative haplotype M. Gray shapes indicate native and Gulf Coast haplotypes (see legend).

w i d e s p r e a d (Fig. 3). Th i s h a p l o t y p e is also com- m o n across E u r o p e a n d c o n t i n e n t a l Asia a n d is m o s t c losely r e l a t e d to haploD~pes f o u n d in t hese p a r t s o f t h e wor ld . I t sha r e s n o n e o f t he m u t a t i o n s t ha t l ink the 11 N o r t h A m e r i c a n h a p l o t y p e s a n d is g e n e t i c a l l y q u i t e d i s t i nc t f i ' om t h e m (Fig. 2; Sa l tonstall 2002) .

Us ing the s a m e 4 g e o g r a p h i c r e g i o n s d e f i n e d abowb s ign i f i can t d i f f e r e n U a t i o n was also o b s e r v e d b e t w e e n m o d e r n p o p u l a t i o n s (p < 0.001). G e n e t i c s t r u c t u r i n g b e t w e e n t h e A t l an t i c Coast , Midwest , \'Vest, a n d G u l f Coas t r e g i o n s was aga in h i g h (Fsw = 0.l 5 -0 .78 ) . G e n e d ive r s i~ ~ was low a l o n g t h e At- l an t i c Coas t (0.09 _+ 0.04) a n d h i g h in t h e Midwes t a n d Wes t (0.(50 _+ 0.03 a n d 0.84 _+ 0.04, r espec t ive - ly).

T h e d o m i n a n t h a p l o t y p e a l o n g t l le At lan t i c Coas t t o d a y is h a p l o t y p e M, wh ich has v i r tua l ly e l i m i n a t e d naUve h a p l o t y p e s fi~om m u c h o f t he a r ea (Tab le 2). H a p l o t y p e ~ , wh ich was r e s t r i c t e d to t h e C o n n e c t i c u t s h o r e l i n e in t he 1800s, was n o t f o u n d in any m o d e r n s p e c i m e n s . H a p l o t y p e F was f o u n d in severa l s a m p l e s a l o n g t h e R a p p a h a n n o c k River in V i r g i n i a a n d h a p l o t y p e Z was f o u n d a l o n g


W i c o m i c o C r e e k in Al len , M a r y l a n d , b u t all o t h e r A t l an t i c Coas t p o p u l a t i o n s s a m p l e d in this s tudy posses sed h a p l o t y p e M.

A l t h o u g h all na t ive h a p l o t y p e s ( h a p l o t y p e s E, G, S) f o u n d h i s to r i ca l ly a r e still p r e s e n t t h r o u g h o u t t he Midwes t a n d s o u t h e r n C a n a d a , h a p l o t y p e M n o w d o m i n a t e s a r o u n d the G r e a t L a k e s a r e a (Fig. 3) a n d is b e c o m i n g c o m m o n a l o n g r o a d s i d e s t h r o u g h o u t t l le r e g i o n . In fact, 84% o f hap lob~pe M s a m p l e s in t he Midwes t were c o l l e c t e d a l o n g r o a d s i d e s o r f i ' om m a r s h e s a l o n g t h e G r e a t L a k e s (Tab le 2).

Na t ive h a p l o t y p e s still d o m i n a t e t h r o u g h o u t t h e S o u t h w e s t ( h a p l o t y p e s A, B, H) a n d m u c h o f t h e Pacif ic N o r t h w e s t ( h a p l o t y p e s A, C, D, E). Few sam- p les o f h a p l o ~ p e M were f o u n d in W e s t e r n p a r t s o f N o r t h A m e r i c a a n d all we re in u r b a n a reas (Ta- b le 2). O n e o t h e r hap lob~pe ( h a p l o ~ p e L) t ha t is n o t c losely r e l a t e d to o t h e r na t ive ~ p e s was f o u n d in a m o d e r n s a m p l e f i 'om Moses L a k e in e a s t e r n \ '~Mshington. Th i s h a p l o ~ - p e is c losely r e l a t e d to f i a p l o t y p e M. H a p l o t y p e I was f b u n d in 2 s a m p l e s a l o n g t h e C o l o r a d o River in Aaizona .

M o d e r n s a m p l e s fYom the G u l f Coas t r e m a i n d o m i n a t e d by h a p l o t y p e I. H a p l o t y p e M a p p e a r s to n o t have b e c o m e w i d e s p r e a d ill this r e g i o n , e x c e p t in t he Miss i ss ipp i River De l t a w h e r e 4 d i f f e r e n t samples , p r ev ious ly f o u n d to possess d i f f e r e n t isozyme p ro f i l e s ( H a u b e r et al. 1991; t I a u b e r p e r s o n - al c o m m u n i c a t i o n ) , d i s p l a y e d h a p l o ~ p e M.

D i s c u s s i o n

T h e h i g h levels o f c h l o r o p l a s t D N A s e q u e n c e v a r i a t i o n d e t e c t e d in this s tudy p r o v i d e a too l f r o m w h i c h to i n t e r p r e t t h e g e n e t i c s t r u c t u r e o f na t ive p o p u l a t i o n s o f Phr~mites in N o r t h A m e r i c a a n d the invas ion p r o c e s s o f n o n n a t i v e l ineages . T h e r e a r e 4 m a i n conc lus ions : t he 11 na t ive N o r t h ~ancr- i can f i ap lo types a r e ge og ra p f i i c a l l y s t r u c t u r e d , with A t l an t i c Coast:, Midwest:, a n d Wes t r e g i o n s all show- i n g s ign i f i can t levels o f d i f lL ' r en t i a t ion fl~om e a c h o the r ; G u l f Coas t p o p u l a t i o n s a r e u n i q u e a n d n o t c losely r e l a t e d to o t h e r Nor f l l A m e r i c a n h a p l o -

TABLE 2. Distribution of haplotype M samples by habitat type found in all modern populations across North America. Roadsides relier to highways, coun/y roads, and railroads. Natural areas include all sites not adjacent to roads, many of which are managed as parks~ wildlife refl~ges, etc. Uudescribed habitat iudicates that insufficiem iuformation was available to assign samples to a habitat (;lass.

[ [aplotype M

I Jndescribed Geographic Region Total Samples HaploTpe M Roadsides Natural A~-eas Habitat

Adantic Coast 105 101 26 57 92 MidwesT-Southern Canada 74 32 97 4* 1 West 37 9 7 1 * ] Gulf Coast t 8 4 0 4 0

Additional information indicates that these sites were historically subject to human disturbance i n the past (e.g., agriculture, mining, deforestation) despite being currently managed as natural areas.

448 K. SaRonstall

types; inw~sive nonnat ive populat ions share a single haplotype (haplotype M) that has overrun the At, lantic Coast and is present t h roughou t the rest of Nor th America; and normative populat ions in the Midwest and West occur along roadsides and wa- terways, support ing the hypothesis that dispersal of Pkrag~nites is facilitated by humans.

NATIVE 'AND (;ULF CC)AST PC)PULATIONS

Eleven native haplotypes were once widely dis- tributed across Nor th iMnerica (Fig. 1; Saltonstall 2002). High lewAs of genetic dift 'erentiation seen between different geographic regions (Fig. 2) sup- por t historical evidence that Pkragmites has been present across the cont inent for thousands of years (Niering et al. 1977; I lansen 1978; Orson 1999; Goman and Wells 2000), allowing it to dift)rentiate at the genetic level across the landscape. Most hap- loD~pes occur in a limited geographic area (Fig. 1 ), and only with o ther closely related hap lo~pes (Fig. 2). It is not known if this relatedness reflects ecological adaptat ion to ditlkwent habitats or simply limited gene flow between different regions of the cont inent (e.g., Athmtic Coast, Midwest, West). Of the 11, only haplotype E was fbund to range ficom the East to West Coasts but its distribution did no t extend into the Southwest U.S. It is most closely related to Atlantic Coast and Midwest hap lo~pes and shares several mutat ions with each of them. Based on the predictions of coalescent theory (Castelloe and Temple ton 1994), this h a p l o ~ p e is the likely ancestor of all native Nor th American Pkrag~nites lineages.

Gulf Coast: populat ions remain dominated by haplotype I, which ranges along the coast fi~om Florida to the Gulf of Califbrnia. It was also tound along the lower Colorado River in Arizona; how- ever Pk~gmites has been planted extensiwAy along the river to stabilize its banks (Yuma Park Service Ranger personal communica t ion) and it is possible that these clones do not represent a natural occur rence of this haplotype in Arizona. The haplo- D~pe most closely related to haplotype I worldwide is h a p l o ~ p e U, which is f ound in Asia (Saltonstall 2002). It is not possible to definitively say whether or no t haplotype I is native to Nor th America based on the data presented here because its distribution remains the same between populat ions sampled in the 1800s versus the 1990s and it is also tbnnd in South America and Asia (Saltonstall 2002).

MODFRN POPULXI'IONS

H a p l o ~ p e M was probably first in t roduced to the Atlantic Coast of Nor th America in the late 1700s or early 1800s (Saltonstall 2002). Today it has spread t h roughou t this region and was found at nearly all sites sampled in this s tu@ These in-

elude brackish and fl~eshwater tidal marshes, non- tidal freshwater sites, river banks and lake shores, and r a i l road and r o a d s i d e p o p u l a t i o n s . This spread, which occur red very rapidly, has replaced native haplotypes that were historically present at many of these sites and appear to have been elim- inated (Saltonstall 2002). It is possible that some of these l ineages--such as haploD~pe AA, which was found in historical samples collected before 1910 in southern Connect icut but was no t found in any m o d e r n samples--have gone extinct as a result of this fiwasion. Haplotype F was quite c o m m o n in historical samples but was restricted to one site in Virginia in the m o d e r n sample. This haplotype, along with haplotype Z that was found at one site in Maryland, persists but its distribution has been greatly reduced. HaploD,pe M has spread south into sites that previously did no t ha rbor Pkrag~nites (Stalter 1975). Haplob,pe M today dominates the Atlantic Coast of Nor th America and has outcom- peted all lineages native to the region.

The Midwest and southern Canada historically conta ined S haplotypes that persist today in wetlands t h roughou t the region. Haplotype E remains the most c o m m o n native type and is widespread. Haplotype M is becoming more prew~lent a round the Great Lakes, particularly along roadsides and lake shores; it has also been found to coexist with native haploD~pes in the same marsh, such as at Montezuma National Wildlife Refi~ge in Seneca Falls, New York. Roadside and lake shore habitats may provide corridors for dispersal of haplotype M Pk~%(mdtes and appear to be facilitating its spread into the Midwest. \;Vhile native populat ions are still c o m m o n in the area, the in t roduct ion and estab- l ishment of haplotype M to the area may pose a threat to them, and m a n a g e m e n t action against newly established populat ions may be warranted where concerns over loss of" native Phragmiles populations exist.

Such actions may be complicated by the ob- served spread of native lineages in the Midwest. A recent paleoecological analysis at Bark Bay Slough, \'Visconsin, along the shores of Lake Superior iden- tiffed several recently established Pk'ra~mites populations. Genetic analysis of 2 of these populat ions fbund them to be haplotype E (Lynch and Salton- stall 2002). Furthel; o ther populat ions exist in Min- nesota that are considered to be spreading and in- w~sive (Eggers personal communica t ion) but were also tbund to be haplotype E.

There are 3 possible explanations fin" this ob- served spread in native populations: native populations are dispersing and establishing in new sites, m u c h as they have for thousands of years; environmental condit ions may have changed such that native vm'ieties m'e now more competitive over o ther

Genetic Variation in North American Phragmites 4 4 9

native marsh vegetation at certain sites, thus facilitating their spread; or while it is not: known when haplotype M first arrived in this region, it is possible that it is breeding with native O'pes and cre- ating a hybrid that possesses a greater competitive abiliD. ~Aqfile none of these scenarios can be addressed directly fl'om the data presented in this analysis, it is clear that major changes in land use and associated changes in hydrology have occur red in many wetlands throughout: the Great Lakes area (Lynch and Saltonstall 2002) and that normative Phragmites is now present in the region (Saltonstall 2002). Tile question of' whether or no t native and haplotype M PhraKmites lineages are crossing is currently being addressed using nuclear microsatellite analysis (SaltonstM1 unpubl ished data).

Based on the analysis presented here, it is clear that most West populations, particularly those in the Southwest, are genetically distinct from Mid- west and Atlantic Coast populations. Five haplo- ~-pes (A-D, H) are restricted to this region and form a distinct g roup (Fig. 2). Haplotype M is rare and fo tmd only in urban areas (e.g., Seattle, Wash- ington, and Salt: Lake City, Utah). In this part of' the country, native Phragmites is typically found along rivers and at desert springs. Few roadside poptfiations are seen, and if' so, only where water is clearly present. The hot, dry condit ions of this region may effectively prevent the spread of haplob,pe M through the area given that appropria te habitat is not common. Haplotype L, which was found in one sample from eastern ~:Vashington, is also found in Europe where it is the second most c o m m o n Phrag~dtes haplotype (Saltonstall 2002). This haplotype may represent a secondary intro- duct ion of' a nonnat ivc genetic type to Nor th ~anerica or it may be the result of a mutat ion in haplotype M that has not: spread beyond the pop- ulafion in which the mutat ion occurred.

At this point, the Gulf Coast region also appears to be largely unaffected by the spread of h a p l o ~ p e M. I Iaplob,pe I dominates f rom Florida west to the Gulf of California, and haplob,pe M was found only along the Mississippi River Delta. Previous studies have Mso shown the Gulf region to be dominated by a single multi locus pheno type with pheno typ ica l ly d is t inc t p o p u l a t i o n s in tile Del ta (Hauber et al. 1991; Pellegrin and Hauber 1999). The normative samples in the Delta may have established fi~om vegetative fl 'agments or seeds wash- ing downriver fl~om upstream rather than fl 'om a local source. Although product ion of viable seed is thought to be low in the region (Fournier et al. 1995), haploO~pe M Ph'ra~mites now covers vast areas of the Delta and its spread to o ther areas of the Gulf Coast via dispersal of seeds or rhizome fi 'agments is clearly possible.

C o n c l u s i o n s

In the absence of ecological information com- paring native and nonnat ive lineages of' Phragmi~es in Nor th Axnerica, it is not: possible to say how haplotype M outcompetes native w~rieties or why it is so aggressiw~'. It is clear that haplotype M has been genetically isolated fl-om the 11 native varieties identified in this study for quite some time and that its arrival in Nor th America is changing the popula t ion structure of the species across the continent. While only 2 states (New Hampshire and South Carolina) presently list Phr~mites as a noxious weed (U.S. Depar tmen t of Agriculture 2002), the rapid expansion of the species has p r o m p t e d widespread eflbrt:s to cont:rol and eradicate Phrag- mil~es populat ions with no regard to their native sta, tns. Now that snch identifications can be conclu- sively made (Saltonstall 2002), m a n a g e m e n t actions can be better targeted toward controll ing nonnat ive populat ions and preserving native ones. I lowever , m a n a g e m e n t s t ra tegies mus t be ap- p roached with caution and an unders tand ing that environmental factors (e.g., changes in hydrologT, tam' lent enr ichment , human development) may also be playing an impor tan t role in the expansion of Phmgmites. As native populat ions are apparently spreading in some sites (Lynch and Saltonstall 2002; Salt:onstall p e r s o n a l observat : ion) , care should be taken to identif}' the origins of popula, tions subject to management . This is particularly impor tan t in the Midwest and Western parts of Nor th ~ n e r i c a , where nat:ire populat ions persist and thrive in many sites.

It is clear that the aggressive nature of haplo~ 'pe M Phmgmites has fundamental ly changed mm'sh communit ies across the Atlantic Coast region and its presence is now being felt in the Midwest and other regions of the country. It is likely that its spread has been facilitated by h u m a n dispersal and will cont inue to do so unless appropria te measures are taken to prevent fur ther spread. Al though eradication of this lineage is unlikely given its widespread distribution, control of its spread to additional sites may be possible and warrant:ed in sites where preservation of native biodiversity is a goal.

ACKNOWLEDGMENTS

Thanks to.]. R. Powell, G. Caccone, M. Donoghue, and.]. S. Hall and 2 anonymous reviewers for comments and discnssions. Jeffrey R. Powell kindly provided the laboratory space and Pa- cilities for this work. I thank those who have provided me with samples. I also thank the U.S. National tierbarinm, ttarvard Universi V Herbaria, New England Botanical Societ?; George Safford Torrey Herbarium at the University of Connecticut, Connecticut Botanical Socie/y, and ~¢ale Universi/y Herbarium for providing herbarium samples. This research was flmded by an Envh:onmental Protection Agency STAR graduate fellowship, The Nature Conservancy Connecticut chapter, The Long Island

4~0 K. SaRonstall

Sound F u n d admin i s te red by the Connec t icu t D e p a r t m e n t of Env i ronmenta l Protect ion t h r o u g h the sale of L ong Is land Sound license plates and contr ibut ions , the New Jersey Public Service Electric aud Gas Company, and the U.S. Fish and Wild- life Service t h r o u g h the Biological Control o f Non- Ind igenous Plant Species Program at Cornell UniversiD; and the National Oceanic and Atrnospher ic Adminis t ra t ion Office of Sea Grant and Exu 'amura l Programs, U.S. D e p a r t m e n t of" C ommerce , under g ran t no. ME R P / S G 99-21. T he U.S. G o v e r n m e n t is .autho- rized to p roduce and distr ibute repr ints for governmenta l put~ pose no twi ths tand ing any copyright no ta t ion tha t may appear hereon . NJSG-02474.

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YUMA PARK SERVICE RANGER. Personal Communicat ion. "Alma Crossing National Heritage Area, 180 West First Street, Yuma, Arizon 85364.

l~ceived jbr co~'tside~t~or~, l'ebrua~ 7 19. 2002 R~,i,sec~ October 2, 2002

Ae~Jted ['or pub~ication, October 30~ 2002

genetic variation among north american populations ofphragmites australis: implications for...

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