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Copyright 0 1994 by the Genetics Society of America

Paternally Inherited Chloroplast Polymorphismin Pinus:Estimation of Diversity and Population Subdivision, and Testsof DisequilibriumWith a Maternally Inherited Mitochondrial Polymorphism

Jinsheng Dong'and David B. Wagner2Department of Forestry, University of Kentucky, Lexington, Kentucky40546-0073

Manuscript received May31, 1993Accepted for publication November 13, 1993ABSTRACT

We have surveyed a chloroplast DNA restriction fragment length polymorphism in745 individuals,distributed rangewide in eight allopatric natural populations ofjack pine(Pin us banksiana Lamb.) andeight allopatric natural populations oflodgepole pine (P inu s contorta Dougl.).The polymorphic regionof the chloroplast genome is located near duplicated psbA genes. Fourteen length variants were foundin the survey, and these variants distinguished the two species qualitatively. Variant diversities werehighin both species ( h , = 0.43 in jack pine; h , = 0.44 in lodgepole pine). Population subdivision was weakwithin and among lodgepole pine subspecies and in jack pine ( i.e . , @valueswere lessthan 0.05).This weaksubdivision iscompatiblewith theoretical predictions for paternally inherited markers in wind-pollinatedoutcrossers, as wellas for polymorphisms with high length mutation rates. If these populations are at adrift-migration equilibrium, the chloroplast DNA restriction fragment data and previous mitochondrialfrequency data from the same individualsare consistent with gene flow that is differential through seedsand pollen. The new data have permitted the first empirical tests of disequilibrium between maternallyand paternally inherited factors. As expected, these tests failed to detect convincing evidenceof non-random association between chloroplast and mitochondrial variants.

AN understanding of the amounts, patterns and as-sociations of genetic variation is a major goal ofpopulation genetics. Such knowledge is fundamentalno t only for tests ofevolutionary hypotheses, but also foreffective germplasm improvement and conservationstrategies.

Plants, unlike animals, have three interdependentge-nomes which reside in nuclei, chloroplasts and mito-chondria. Thus, plant population geneticists face thecomplexity that genetic variation occurs in as many asthree, differently inherited, compartments.

Theoretical analyses have anticipated that genetic s u bdivision among populations is sensitive to mode of inher-itance. For example, matemally inherited cytoplasmicvariation in plants is expected to exhibit greater popula-tional differentiation at equilibrium than nuclear genes,asa consequence of (i) migration of maternally inheritedorganelles through seeds, but notpollen, and (ii) the d i ploid nuclear but haploid organellar composition of seeds(BIRKY1988;PETITet al. 1993a). In fact, maternallyinher-ited chloroplast polymorphisms often do involve differ-ences among populations [SOLTISet al. (1992) and refer-ences therein]. Similarly,maternally inherited plantmitochondrial polymorphisms (DONGand WAGNER1993;STRAUSSet al.1993) havepopulation subdivision statisticsashigh as 0.96.

' Permanentaddress:JiangxiAgriculturalUniversity, Nanchang, Jiangxi* To whom correspondence should be addressed.Province, People's Republic of China.

Genetics 136: 1187-1194 (March, 1994)

Chloroplast DNA (cpDNA) in conifers and someother plants is paternally (o r atleast predominantly pa-ternally) inherited ( e . g . ,SCHUMANNand HANCOCK1989;BOBLENZet al. 1990; WAGNER1992). In contrast to ma-ternally inherited loci, paternally inherited loci can mi-grate through both seeds and pollen [considerPROUT(198 l) l. Consequently, population subdivision of neu-tral, paternally inher ited factors is expected to be weakerthan that of maternally inherited factors in outcrossingplants, when the mutation rateis lower than the migra-tion rate, especially when pollen migrates more effec-tively than seeds (PETITet a l. 1993a). This expectationdoes not require that paternal inheritance bestrict, butholds true even with considerable maternal leakage(PETITet al. 1993a). Empirical population subdivisionestimates arerarefor paternally inherited polymor-phisms, but subdivision can be substantial when rnigra-tion is infrequent or absent (HONGet al. 1993;WANGandSZMIDT1993).

Like population subdivision,genotypicassociationsamong loci (disequilibria) may hinge on modes of inher-itance. For example, nonrandom associations between pa-ternally inherited and maternally inherited cytoplasmic ge-nomes should disappear rapidlyinoutcrossingpopulations (SCHNABELand ASMUSSEN 1989). Cytonuclearpopulation genetic data, though uncommon in plants,have begun toaddressmitochondrial-nuclear andchloroplast-nuclear associations(PAIGEet al. 1991; SAGHAIMAROOF et al. 1992). However, the prediction of random


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1188 J. Dong and D. B. WagnerTABLE 1

Sample site locations (abbreviationsin parentheses),taxonomic classificationsand sample sizes

Taxonomic SampleLocation a classification size

Doaktown, New Brunswick (NB) P .b . 50Lac Mathieu, Quebec (PQ P .b. 50Chalk River, Ontario (ON-E) P. b. 49Wellston, Michigan (MI) P . b. 47Raith, Ontario (ON-W) P .b. 43Hadashville, Manitoba (MB) P . b. 46Canwood, Saskatchewan (SA) P .b. 47Bellis, Alberta (AB) P .6 . 48Mackenzie, British Columbia (BGN) P .c. 1. 44Prince George, British Columbia (BGC) P .c .1. 43Lumby, British Columbia (BGS) P .c. 1. 43Ward, Colorado (CO) P . c. 1. 49Prince Rupert, British Columbia (BC-W) P .c. c. 43Waconda Beach, Oregon (OR-W) P .c. c. 46Santiam Pass, Oregon (OR-C) P .c .m. 47Wrights Lake, California (CA) P .c .m. 50Most locations are in Canada, exceptMI, CO, OR-W, OR-C, andC A , which are in the UnitedStates. Map locations are shown inDONGand WAGNER(1993).P. banks iana .P . contorta var. latijolia.P . contorta var. contorta.P . contorta var. murrayana [for a discussion of taxonomic classi-fication of OR-C popula tion, see WHEELERand CURIES(1982)l.association between paternally and maternally inheritedfactors has not been tested.

Here we study natural populations ofjack pine(Pinusbanksiana Lamb.) and lodgepole pine(Pinus c o n t o r t aDougl.) (i ) to estimate population subdivision param-eters of a paternally inherited cpDNA polymorphismand (ii) to test statistical associations of chloroplast andmitochondrial DNA variants. These two much studiedNorth American pines (PinusL.) are widely distributed,closely related, wind-pollinated outcrossers, and they hy-bridize naturally in sympatric regions of western Canada(CRITCHFIELD1985). They comprise an unusually valu-able genetic system because of their paternal chloro-plast, yet predominantly maternal mitochondrial, inher-itance (WAGNERet a l. 1987,1989,1991;DONGet a l . 1992;DONGand WAGNER1993). Because isoenzyme(i. e . , Men-delian) and mitochondrial surveys have already beenreported in jack and lodgepole pines (WHEELERandGURIES1982, 1987; DONGand WAGNER1993), our newdata allow immediate comparisons of population struc-ture among three,differently inheri ted, plantgenomes.

MATERIALSANDMETHODSPlant materials:The germplasm collections have been de-scribed in detail elsewhere (DONGand WAGNER1993). Briefly,745 individuals were sampled, representing eight allopatricnatural populations of each species (Table 1).Sampled popu-lations were distributed rangewide in both species and in-cluded three of the four lodgepole pine subspecies. The avail-able samples provided approximately 95% power to detect

variants that were present ( i ) with frequency 20.07 within agiven population and ( i i ) with overall frequency 20.004.

Laboratory methods:We elected to examine a single highlyvariable chloroplast polymorphism, rather than several mark-ers of lower variability.This choice maximized the numbersofindividuals and populations that could be surveyed, given theavailable resources. After preliminary surveys, the particularpolymorphism chosen for this study was selected because(i ) it was the only cpDNA polymorphism known to vary in-traspecifically in both study species and( i i ) its paternal in-heritance had been demonstrated (WAGNERet al. 1987,1989;GOVINDARAJUet al . 1989; DONGet al. 1992).Each sampled individual was classified by it s variant of anSstI restriction fragment length polymorphism (RFLP), as de-scribed previously (WAGNERet al . 1987; DONGet al . 1992). Inthepresent study we found thata 7.4kilobase-pair (kbp)Hind111 fragment and a 700-base pair (bp) BamHI-SmaI frag-ment from the lodgepole pine chloroplast genome (LIDHOLMand GUSTAFSSON1991) could beused interchangeably asprobes in molecular hybridizations. The psbA gene is dupli-cated in jack and lodgepole pines (LIDHOLMet al . 1991), andeither of these probes reveals insert ion/deletion polymor-phismassociatedwith the psbAZ-PsbAZZ genomic region(GOVINDARAJU et al . 1989;J. DONGand D. B. WAGNER,unpub-lished results). Although our focus here is not the moleculardetails of this polymorphism,it is relevant that atleast someof its variability is due to copy-number variation of shorttandem repeats(LIDHOLM and GUSTAFSSON1991). Thispolymorphism is clearly a hot spot of chloroplast leng thvariants in jack and lodgepole pines (WAGNERet al. 1987;GOVINDARAJUet al. 1989).Data analysis: Frequency data from the 16 populations(Table 2) were used to estimate: numbers ofvariants in species( A s )and populations ( A , ) (HAMRICKand GODT 1990), unbi-ased variant diversities in species( h , ) and populations (he,)(NEI1978), and population subdivision (WRIGHT1951). Popu-lation subdivision was estimated as 8 by the method describedby WEIR(1990, p. 150),and the statistical significance of dif-ferentiation among sampled populations was evaluated by chi-square tests (WEIR 1990, p. 137).Mitochondrial data from a COXZZ-associated length poly-morphism were availablefor 740 of the same individuals stud-ied here (DONGand WAGNER1993). Therefore, we used chi-square analyses oftwo-factor contingency tables to teststatistical associationsbetween chloroplast and mitochondrialvariants. These tests were performed( i ) within each of theseven populations ( P Q ON-E, SA, BC-N, BGC, OR-W, OR-C)that were variablefor both chloroplast and mitochondrial poly-morphisms [see Table 1 of DONGand WAGNER(1993); Table2 of this study], and (ii) at the species and subspecies levels bypooling data from populations within species and withinlodgepole pine subspecies.

RESULTSDiversity: By any standard, levels of variation were

high in both species (Tables2 and 3).Fourteen variantswere found in the total survey, eight in jack pineand sixin lodgepole pine. The number of variants per popu-lation ranged from 2 to 6 ,averaging 4.5 injack pine and4.0 in lodgepole pine.

Variant diversities at the species level(hes)were simi-lar in jack and lodgepole pines (0.43 and 0.44, respec-tively). Within-population diversities ( hep) alsowerecomparable in the two species, ranging over all p o p -lations from 0.22 to 0.66. Notably, no population wasfixed for a single cpDNA variant (Tables 2 and 3).


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cpDNA PopulationGenetics in Pinus 1189TABLE 2

Chloroplastvariant frequencies in 16 populations of P. banksiana and P. contortaP. contorta populations

var. Var. V U .P. banks iana populations latifoliacontortamurrayana

Variant" NB PQ ON-EMION-WMB SA AB BGN BGC B G S CO BGWOR-W ORGb CA4 .4 / 5 . 74 . 7 / 5 . 74 .8 / 5 . 75 . 0 / 5 . 74 .3 / 4 . 8 / 5 . 75 . 0 / 5 . 5 / 6 . 25 . 5 / 6 . 2 / 6 . 74 . 3 / 5 . 04 . 4 / 5 . 04 . 5 / 5 . 04 . 7 / 5 . 04 . 3 / 4 . 5 / 5 . 04 . 3 / 4 . 7 / 5 . 0

4 .7 / 4 . 9 / 5 . 7

0.02 0.10 0.020.10 0.14 0.160.170.76 0.62 0.710.660.04 0.150.06 0.10 0.060.020.06 0.020.02

0.020.020.06 0.070.260.09 0.130.880.70 0.81 0.770.02 0.04 0.06 0.040.02

0.070.120.040.190.110.020.02 0.090.140.16 0.08 0.09 0.13 0.090.040.73 0.65 0.84 0.86 0.53 0.610.79 0.860.110.090.140.130.11 0.080.05 0.020.02

Location abbreviations are defined in Table 1 [see also DONGand WAGNER(1993)l.'Variants are denoted by restriction fragment sizes (in kilobase pairs); only the variable fragments are listed, separated by slashes withineach* See WHEELERand GUNES(1982) for discussion of subspecies taxonomic classification in this geographic region.variant.

TABLE 3Population genetic statistics for a chloroplast polymorphismin P.banksiana and P . contorta

P . contorta populationsvar. V W . var.P. banks iana populations latifolia contortamurrayana

Statistic" NB PQ ON-E MION-WMB SA AB BGN BGC BGS CO BGWOR-W OR-Cb CAA, 55 3 5 4h ,

44 2 4 5 5 440.41 0.590.470.520.220.460.340.390.460.55 0.28 0.260.660.600.370.26Mean A,Mean h,A,h,e

4.500.4280.430.02; P < 0.01

4.000.4360.440.04 (among subspecies); P < 0.0010.02 (withinvar. latifolia); P < 0.05'0.00 (withinvar. contorta): NS '0.00 (within var. murrayana ) ; N S ~, I

Populations as described in Table 1.'Abbreviations for population genetic statistics are defined in the text.b A s in Table 2.Chi-square probabilities.Differentiation: Chloroplast DNA variantsunam-biguously distinguishedjack pine from lodgepc'e pine

(Table 2), as in previous work(WAGNERet a l. 1987).However, the earlier work sampled few individuals perpopulation, precluding formal analysis of populationsubdivision.

Seved of the chiquare tests indicate statistically signifi-cant (P


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1190 J. Dong and D. B. WagnerTABLE 4

Tests of association between chloroplast and mitochondrialvaliants

Population(s)PQON-ESABGNBGCOR-CP . b a n k s i a n a bP. contortabP. contorta var. lat i jol iabP. contorta var. contortabP. contorta var. m u r r a y a n a b

OR-W

Chi-squarevalue13.560.415.001.310.557.082.6714.3334.9011.025.792.36

d.f.45833832120883

Probability0.010.990.760.730.910.530.450.850.020.200.670.50

This table includes populations that were polymorphic for chloro-plast and mitochondrial markers. Location abbreviations are definedin Table 1.a This chi-square value was reduced to2.53 (with one degree offreedom (d.f.), P = O.ll), when a cell with expected frequency lessthan one was removed from the contingency table by pooling rarecpDNAvariants into a synthetic variant.* Data were pooled within species or subspecies prior to tests indi-

cated by this superscript.This chi-square value was reduced to21.76 (with 12 degrees offreedom, P = 0.04), when cells with expected frequencies less thanone were removed from the contingency table by pooling rare c pDNA variants in to a synthetic variant.expected frequenciesless than one. Theselow expectedfrequencies were removed by pooling cells withrare vari-ants, which increased the chi-square probability to 0.04.

DISCUSSIONDiversity: Two of the cpDNA variants found in this

survey (5.0/5.5/6.2 and 5.5/6.2/6.7) have not beenreported previously. These bring the total number ofpsbA-associated variants now known in jack and lodge-pole pines to 36, in a total sample size of nearly 2300individuals (WAGNERet al. 1987;GOVINDARAJU et al. 1988;GOVINDARAJU et al. 1989;WAGNERet al. 1989;DONGet al.1992). This is clearly a minimum estimate of the totalnumber of variants, because small differences (of about50 bp or less) in restriction fragment sizes would havebeen unresolved on autoradiograms.

Many of the psbA-associated variants are individuallyrare and are concentrated in or near a geographic re-gion of sympatry between thetwo species. A previousreport discussed several possible causes for these rarevariants, including natural hybridization an d evolutionin marginal populations (GOVINDARAJUet al. 1989).Three rare variants of the present study(4.3/4.5/5.0;4.3/4.7/5.0;4.7/4.9/5.7) werepreviously detectedonly in or near regions of natural hybridization. Butthese three variants, as well as the two newly discoveredvariants, occurred hereonly in marginal allopatric popu-lations (NB, ON-E, CO, BC-W,OR-W) thatare far-removed from regions of sympatry.Thus, although natu-ral hybridization may be involved in the production of

certain rarecpDNAvariants, it cannot be theonly cause.Thorough understanding of mechanisms responsiblefor generatingall these variants will require detailed in-vestigation at the molecular level.

Th e psbA-associated cpDNA variability in jack andlodgepole pines, whether measured in termsof variantnumber or diversity (Table 3), appears remarkable.Nonetheless, the high level of variabilitydoes not con-tradict the generally slow rate of chloroplast sequenceevolution (WOLFEet al. 1987; CLEGGet a l. 1991), for atleast two reasons.

First, although we have not elucidated the molecularbasisof all the variants, it is known from several lines of evidencethat the psbA-associated polymorphism results primarily frominsertion/deletionmutation (G~VINDARAJUet al. 1989;LJDHOLM and GUS~AFS~ON1991). Short tandem repeatshavebeen implicatedhere and inother systems in generating highlevels of cpDNAlength variation (PALMERet aL 1987;h ~ metd 1988 ;B ~ ~ oe ta l .1988;OGIHARAetaL 1988;hetal.1991;LIDHOLMand GUS~AFS~ON1991).Clearly,data from polymor-phisms that arise through length mutation are unrelatedtogeneral conclusionsabout chloroplast base pairsubstitutionrates.

Second, recall that we chose to study a single hot spotof cpDNA polymorphism, precisely because ofa prioriknowledge of it s intraspecific variability (WAGNERet al.1987). Thus, thediversity of this polymorphism shouldnot be viewed as typical. Several but not all other in-vestigators of cpDNA diversity,including those who haveexamined point mutations, have also emphasized poly-morphic regions of the chloroplast genome in their sur-veys ( e . g . , compare methodologies of WHITTEMOREandScm 1991; HONGet al. 1993; WANGand SZMIDT 1993;PETIT et al. 199313). Consequently, the cpDNA populationdata that is accumulating inthe literature must be treatedcautiously and appropriately when inferring generalitiesregarding diversity in the chloroplast genome.

Despite these caveats, intraspecific cpDNA hot spotscarry useful information. Their high diversities, com-bined with uniparental inheritance (usually maternal inangiosperms but usually paternal in conifers), empowernew fields of inquiry, such as cytonuclear populationgenetics (ASMUSSEN et al. 1987).In this regard, it is prom-ising that the high diversities we report here are notunique; examples of intraspecific cpDNA diversityexisteven for site mutations ( e . g . ,SOLTISet al. 1992 and ref-erences therein; WANGand SZMIDT1993; PETITet al.1993b).

Differentiation: At the species level, it is not surpris-ing that cpDNA polymorphism distinguishes jack fromlodgepole pine. Chloroplast variation occurs commonlyamong plant species, even among closely related ones,and has been much-used in phylogenetic analyses(PALMER 1987; SOLTISet al. 1992).Although intraspecificcpDNA variation and introgression can potentially con-found phylogenetic investigations (DOYLE 1992; SOLTIS


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cpDNAPopulationGenetics in Pinus 1191et a l. 1992;RIESEBERG and BRUNSFELD1992), itis encour-aging for biosystematists that the psbA-associated c pDNA variants of jack and lodgepole pines show no spe-cies ambiguity (despite substantial intraspecificvariability). However, note that some individual restric-tion fragmentsizes ( e . g . ,the 4.4kbpsize class)do occurin both species, which indicates theimportance ofscreening alarge number of restriction fragments whenseeking cpDNA species markers.

Consistent with drift-migration equilibrium predic-tions for paternally inherited neutralpolymorphisms inoutcrossers (PETITet al. 1993a), psbA-associated differ-entiation among conspecific jack and lodgepole pinepopulations is weak and roughly similar to nuclear sub-division in these species. For example, psbA-associated 8is 0.04 amonglodgepolepine subspecies (Table 3 ),while a corresponding isoenzyme statistic(GJ is 0.03(WHEELERand GURIES1982).In contrast, population subdivision of maternally in-herited mitochondrial DNA length variants,estimatedfrom the same D N A samp les that we usedfor the chlo-roplast analyses , is much higher( e . g . ,8 = 0.31 amonglodgepolepine subspecies, an d 8 isas high as0.82amongpopulations within subspecies; DONG andWAGNER1993). Recall that, given sufficient intraspecificvariability, maternally inheri ted polymorphisms in otherplants also generally exhibit considerable subdivisionamong populations (SOLTISet a l . 1992; STRAUSSet al.1993; PETITet a l . 1993b).

As in jack and lodgepole pines, population subdivi-sion may be weak for paternally inherited slash pine( P inusel l io t t i i Engelm.) cpDNA length variants(WAGNERet al. 1992). However, WANGand SZMIDT(1993)recently found that population subdivision of cpDNAhaplotypic diversity in P inus de nsa ta (G, , = 0.181) isrelatively high in comparison with psbA-associated sub-division in jack an d lodgepole pines. This result forP. de nsa ta appears to contrast with neutral equilibriumpredictions under drift and migration (PETITet al.1993a), possibly due to the hybrid origin of this species(WANGand SZMIDT1990).

Again in apparent contrast to drift-migration predic-tions an d our results in jack and lodgepole pines, sub-division of paternally inherited cpDNA site mutationhaplotypes in bishop pine ( P i n u s m u r i c a t aD. Don) isstrong (G,, = 0.842) among geographic regions (HONGet al. 1993). There are atleast two, possibly interacting,potential causes of the discrepancy.

First,jack and lodgepole pines occupy vast, frequentlycontinuous, geographical ranges in North America, withample opportunities for gene flow (CRITCHFIELD1985;GOVINDARAJU1988).Bishop pine populationscan be geo-graphically and reproductively isolated (CRITCHFIELDand LITTLE1966;MILLARand CRITCHFIELD1988), andge-netic exchanges among populations from differentgeo-graphic groups may be exceedingly rare even through

pollen. Indeed, the proportion of isoenzyme variationthat is attributed to population differences in bishoppine (22%) (MILLARet al. 1988) is much greater than istypical for other conifers including jackand lodgepolepines. For these an d other reasons HONGet al. (1993)consider thesouthernand north-intermediate geo-graphic groups of bishop pine populations to be sepa-rate species. In this connection, it is important to notethat populationsubdivision of cpDNAsite mutation h a plotypes in bishop pine is lower withingeographic groupsthan among geographic groups. For example, subdivi-sion among populationsof the southern group does nodiffer significantly from zero.

Second, cpDNA mutational mechanisms may influ-ence the apportionmentof variation within and amongpopulations. Equation (21) of BIRKYet a l. (1989) indi-cates that population subdivision at equilibrium is in-versely related to mutation rate. Chloroplast site muta-tion rates may be considerably lower than rates of lengthmutation (CLEGGet a l. 1991;AL I et al. 1991). Hence,inthe absence of migration, site mutations might be ex-pected to exhibit greater population subdivision thaninsertion/deletion polymorphisms.

Indeed, there may be a relationship between subdi-vision and mutational mechanism in the species com-plex that includes bishop pine (HONGet a l . 1993). Therelationship is unclear, however, because populationsubdivision of a cpDNA length polymorphism variedfrom G,, = 0.073 in Monterey pine ( P i n u s r a d i a t aD.Don) to G,, = 0.682 in knobcone pine( P i n u s a t t e n u a t aLemm.).

Since the psbA-associated polymorphism of jack andlodgepole pines is due primarily to length mutation, thelow 8 values within each of these two species could bedue to a high length mutation rate. If population sub-division is at a muta tiondrift equilibrium, we can esti-mate the number of new mutants( N , u ) each genera-tion. For example, assuming a neutral equilibrium, nomigration, a large number of demes, and substitutingour P. contorta var. Zatifolia 8estimate (0.02) as GS fintoEquation 21 ofBIruwet a l. (1989),we obtain N,,u = 24.5.Twenty-four newmutants each generationimplies a veryhigh mutation rate, even with large population sizes.In fact, the psbA-associated length mutation ratemustbe greater than the migration rate if mutation is pre-dominantly responsible for the low population subdivi-sion of this polymorphism. This is because mutation andmigration enter in exactly the same way into the equi-librium formula for organellar population subdivision[Equation 21 ofBIRKYet al. (1989)l.

But migration is a potent evolutionary force in jackand lodgepole pines ( e .g . , N ,mbased on isoenzymes av-erages 6.23 in P. contor ta var. l a t i f o l i a ) (GOVINDARAJU1988), andmigration can virtually eliminate populationsubdivision for paternally inheritedplantgenomes(PETITet a l. 1993a). Thus,it seems likely that differential


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1192 J. Dongand D. B. Wagnermigration through seed and pollen is at least partly re-sponsible (probably in concert with a high cpDNAinsertion/deletionrate) for the simultaneous occur-rence in jack and lodgepole pines of(i )weak popula-tion subdivision of psbA-associated cpDNA length vari-ants (Table3) and (ii)strong populationsubdivision ofmitochondrial variants (DONGand WAGNER1993).

Quantitative assessment of the relative importance ofmutation and migration for homogenizing cpDNA vari-ant frequencies among jackand lodgepole pine popu-lations must await surveys of cpDNA point mutationsand estimation of psbA-associatedlength mutationratesin these two species. Unfortunately at present, cpDNApoint mutations are unknown to us within either speciesand in vivo estimation of intraspecific cpDNA lengthmutation rates is a formidable, if not impossible, task.

Interestingly, all but one individual in the CO popu-lation had cpDNA variants typical of lodgepole pine(Table 2 ) . Yet this same population is fixed for a pri-vate (SLATKIN1985) mitochondrial variant (DONGandWagner 1993). A Coloradopopulation also differedfrom more central populations in an isoenzyme study(WHEELERand GURIES1982). If migration and drift areresponsible for these patterns, this information is consistent with a dearth of seed migrationbut more frequent ormore recent pollen migration involving Colorado popu-lations, whichare at the periphery of lodgepole pines cur-rent distributional range. Similarly, the high frequency oftwo private mitochondrial variants inthe OR-W population(DONGand WAGNER1993) contrastswith the cpDNA data(Table2), which againmay be consistent with differentialgene flow through pollen and seeds.

Chloroplast-mitochondrial associations:Statistical as-sociations (disequilibria) between two organellar locidecay rapidly within populations when one locus is pa-ternally inherited while the otherlocus is maternally in-herited (SCHNABELan d ASMUSSEN 1989).Furthermore, asufficiently high cpDNA insertion/deletion rate intu-itively should lead to low or zero chloroplast-mitochondrial disequilibrium (but we are unaware ofany formal reports regarding the effects of mutationrates on disequilibria among cytoplasmic genomes;M.A. ASMUSSEN,personal communication). For thesereasons, a general lack of significant associations be-tween chloroplast and mitochondrial variants was to beexpected in most jack and lodgepole pine populations.

Despite these general expectations, the random as-sociations observed in the SA jack pine populationmaybe a bit surprising because of the high proportionoflodgepole pine mitochondrialgenotypes that remaininthis unusual population after past introgressive hybrid-ization (DONGand WAGNER1993). The decoupled na-ture of chloroplast and mitochondrialinheritance,and/or a high cpDNA insertion/deletion rate, appearsufficient in this population to obscure epistatic fitnesseffects (if such effects exist) of interspecific physiologi-

cal interactions between the chloroplast and mitochon-drial genomes (HUSKet al. 1987).

We note, however, thatthe available sample sizeswould be too small to detect weak associations withinpopulations [ e . g . ,BROWN(1975)l.In this connection, itis interesting that associations were also nonsignificantin the larger sample sizes ofthe species-level testin jackpine (with N = 378) and the subspecies-level tests inlodgepole pine(Table 4) .The significance of the lodge-pole pine species-level association( P= 0.04) may be astochastic consequence of performing 14 statistical testsof association (Table 4) or of pooling data from popu-lations and subspecies with statistically heterogeneousvariant frequencies (PROUT1973).

Conclusions: Pines represent an unusual model sys-tem for population and evolutionary genetic investiga-tions because of their opposite chloroplast and mito-chondrialinheritances. Inthe caseof jackandlodgepole pines, patterns of population subdivision ofvariants in thethree major eukaryotic genomes, to-gether with predominantly random associations be-tween chloroplast and mitochondrial variants, conformwith theoretical predictions for outcrossers. Specifically,a maternally inheritedmitochondrial polymorphismfeatures abundant population subdivision (DONGandWAGNER1993),while Mendelian allozymes and a pater-nally inherited cpDNA insertion/deletion polymor-phism display relativelylittle differentiation among con-specific populations (WHEELERand GURIES1982) (thisstudy, Table 3) . Plant biologists, by considering themode of inheritance of genetic markers, would appearto have the luxury of selecting characters with appro-priate levels and patterns of variation for investigation ofa wide array of unresolved population and evolutionarygenetic questions.

We thank J. LIDHOLMfor his lodgepole pine cpDNAlibrary;V, ASHLEY, M. CARLSON, G. CROOK,N. DHIR,J. DOJACK, D.HEBB,K KELLY,P. KNOWLES, L. LAI, P.MACDONALD,R. MACDONALD,S. MAGNUSSEN,J. MITTON,R. MULLER,D. NEALE,D. PALAMAREK,R.PETIT,W. RANDALL,M. SANDS,J. SCHILF,D. SIMPSON,P. STOVER,R. STUTTS,L. USISKIN,N . WHEELER andD . YMGUCHI for authorizations, accommodationsand other invaluable assistance duringfield collections; H. HA M I L T ON ,T. LI , R. PATEL andD. TALBOT for laboratory assistance;Y.-P. HONG,V. D. HIPKINSand S. H. STRAUSSfor exchanging chloroplast surveydata and manuscriptsprior to publication; and C.W. BIRKY,JR . ,K. KRUTOVSKII,R. PETIT,B. SCHAAL, S. STRAUSS,A. SZMIDT,X.-R. WANG,B. S. WEIR and ananonymous reviewer for suggestions on an earlierversion of this paper.This research (Kentucky Agricultural Experi-ment Station Paper No. 93-8-11) was supported in part by the U.S.Department of Agriculture(grants90-37290-5681 and KYO0640 toD.B.W.), a University of Kentucky Doctoral ResearchAward (toJ.D.),KentuckyAgriculturalExperimentStation funds, and theBritishColumbia Ministry of Forests.

LITERATURE CITEDA L D R I C H, J. , B. W. CHERNEY,E. MERLINand L. CHRISTOPHERSON,1988 The role of insertions/deletions in the evolutionof the

intergenic region between p s b A and trnH in the chloroplast ge-nome. Curr. Genet. 14: 137-146.


7/8

cpDNA Population Genetics in Pinus 1193A L I , I. F., D.B. NEALE andK. A. MARSHALL,1991 Chloroplast DNA

restriction fragment length polymorphism in S e q u o i a s e m p m i -rens D. Don Endl., Pseudotsuga m enziesi i(Mirb.) Franco, Calo-cedrus decurrens(Torr.), andPinus taedaL. Theor. Appl. Genet.81: 83-89.

ASMUSSEN,M. A.,J. ARNOLDandJ. C. AVISE,1987 Definition and p ro perties of disequilibrium statistics for associationsbetween nuclearand cytoplasmic genotypes. Genetics 115: 755-768.BIRKY,C. W.,JR., 1988 Evolution and variation in plant chloroplast andmitochondrial genomes, pp. 23-53 in Plant Evolutionary Bi ob a, ed-ited by L. D.GcyrruEB and S.K. JAIN.Chapman & Hall, London.BIN, C. W., JR., P. FUERST an d T.MARUYAMA,1989 Organelle genediversity under migration, mutation, and drift: equilibrium ex-pectations, approach to equilibrium, effectsof heteroplasmiccells, and comparison to nuclear genes. Genetics 121: 613-627.BIASKO,IC, S. A. KAPLAN, K. G . HIGGINS,R. WOLFSONand B. B. SEARS,1988 Variation in copy number of a 24base pair tandem repeatin the chloroplast DNA of Oenothera hookeri strain Johansen.Curr. Genet. 14 287-292.BOBLENZ,K, T. NOTHNACELand M. METZIAFF,1990 Paternal inher-itance of plastids in the genusD a u c u s . Mol. Gen. Genet. 220:

BROWN,A. H. D., 1975 Sample sizes required to detect linkage disequi-librium betweentwo or three loci. Theor. Popul. Biol. 8 184-201.CLEGG,M. T., G. H. LEARNand E. M. GOLENBERG,1991 Molecularevolution of chloroplast DNA, pp. 135-149 in Evolu t i on at theMolecular Level ,edited by R. K. SELANDER,A. G. CLARK andT. S.WHITTAM.Sinauer Assoc., Sunderland, Mass.CRITCHFIELD,W.B., 1985 The late Quaternary history of lodgepoleand jack pines. Can. J. For. Res. 15: 749-772.CRITCHFIELD, W. B.,and E. L. LITTLE,JR., 1966 Geographic Distribu-t i on of the Pinesof the World.U.S.D.A. Forest Sewice Miscell.Publ. 991, Washington, DC.DONG,J., and D.B. WAGNER,1993 Taxomonic and population dif-ferentiation of mitochondrial diversity in Pinus banks ianaandPinus contor ta .Theor. Appl. Genet. 8 6 573-578.DONG,J., D. B. WAGNER,A. D.YANCHUK,M. R CUUSON,S. MACNUSSENe t a l . , 1992 Paternal chloroplast DNA inheritance inPinus con-torta and Pinus banks iana:independence of parental species orcross direction. J. Hered. 8 3 419-422.

DO=, J.J., 1992 Gene trees and species trees: molecular systematicsas onecharacter taxonomy. Syst. Bot.17: 144-163.GOVINDARAJU,D. R., 1988 Relationship between dispersal ability andlevels of gene flow in plants . Oikos52: 31-35.~ V I N D A R A J U ,D.R.,D.B. WAGNER,G. P. SMITHand B.P. DANCIK,1988 Chloroplast DNA variation withinindividual trees of aPinus banksiana-Pinus contortasympatric region. Can. J. For.Res. 18 1347-1350.GOVINDARAJU,D. R., B. P. DANCIKand D. B. WAGNER,1989 Novel c h broplast DNA polymorphism in a sympatric region of two pines.J.Evol. Biol.2 49-59.

HAMRICK, J. L., and M. J. W. GODT,1990 Allozyme diversity in plantspecies, pp. 43-63 in Plant Populat ion Genet ics, Breeding, a ndGenetic Resources,edi ted by A. H. D. BROWN,M. T. CLEW,A. L.KAHLER and B. S. WEIR.Sinauer Assoc., Sunderland, Mass.HONG,Y.-P., V. D. HIPKINSand S. H. STRAUSS,1993 Chloroplast DNAdiversity among trees, populations and species in the Californiaclosed-conepines ( P i n u s r a d i a t a , P . m u r i c a t aand P . a t t e n u a t a ) .Genetics 135: 1187-1196.HUSIC,D.W., H. D.Husrc and N.E. TOLBERT,1987 The oxidativephotosynthetic carbon cycle or C, cycle. CRC Crit. Rev. Plant Sci.5: 45-100.LIDHOLM,J., and P. GUSTAFSSON,1991 The chloroplast genome of thegymnosperm Pinus contorta:a physical map an d a complete col-lection of overlapping clones. Cum. Genet. 20: 161-166.LINDHOLM,J., A. SZMIDTand P. GUSTAFSSON,1991 Duplication of thePsbA gene in thechloroplast genome of two P i n u s species. Mol.Gen. Genet. 226: 345-352.MILLAR,C. I., an d W. B. CRITCHFIELD,1988 Crossability and relation-ships of Pinus murica ta(Pinaceae). Madrono 35: 39-53.M I ~ ,C. I., S. H. STRAUSS,M. T. CONKLEand R D. W ~ A L L ,1988 Al -lozyme differentiation and biosystematicsof the Californian closed-cone pines (Pinus subsect Oomqae).Syst. Bot 13: 351-370.

NEI,M., 1978 Estimation of average heterozygosity an d genetic di etance from a small number of individuals.Genetics89: 583-590.

489-491.

OGIHARA,Y., T. TERACHIand T. SASAKUMA,1988 Intramolecular re-combination of chloroplast genome mediated by short direct-repeat sequences in wheat species. Proc. Natl. Acad. Sci.USA 8 58573-8577.PAIGE,K. N., W. C.CAPMAN and P. JENNEI?EN, 1991 Mitochondrial inherit-ance patternsacross a cottonwood hybrid zone: cytonuclear disequi-libria and hybrid zonedynamics.Evolution& 1360-1369.

PALMER,J. D., 1987 Chloroplast DNA evolution and biosystematicuses of chloroplast DNA variation.Am. Nat. 13 0 S6-S29.PALMER,J. D.,J. M. NUGENTand L. A. HERBON,1987 Unusual structureof geranium chloroplast DNA a triple-sized inverted repeat, ex-tensive gene duplications, multiple inversions, and two repeatfamilies. Proc. Natl. Acad. Sci. USA84: 769-773.PETIT,R. J., A. K E R and D. B. WAGNER,1993a Finite island modelfor organelle and nuclear genes in plants. Heredity 71: 630-641.PETIT,R.J.,A. KREMERand D. B. WAGNER,1993b Geographic structureof chloroplast DNA polymorphisms in European oaks. Theor.Appl. Genet. 87: 122-128.

PROUT, T., 1973 Appendix, pp 493-496 in Populat ionGenet ics ofMarinePelecypods. Vol. III . Epistasis betweenFunctionally Re -lated Isoenzym esof Myti lus edul is,authored by J. B. MITTONandR. K. KOEHN.Genetics 7 3 487-496.PROUT,T., 1981 A note on the island model with sex dependentmigration. Theor. Appl. Genet. 5 9 327-332.RIESEBERG,L. H., and S. J. BRUNSFELD,1992 Molecular evidence andplant introgression, pp. 151-176 in MolecularSystematics ofPlant s , edited by P. S. SOLTIS,D. E. SOLTISand J. J. DOXE.Chapman & Hall, New York.SAGHAIMAROOF, M. A,, Q. ZHANG,D.B.NEALE and R.W. A L ~ ,1992 Associations between nuclear loci and chloroplast DNAgenotypes in wild barley. Genetics131: 225-231.

SCHNABEL,A, , and M. A. ASMUSSEN,1989 Definition and properties ofdisequilibria within nuclear-mitochondrial-chloroplastand othernucleardicytoplasmic systems. Genetics 123: 199-215.SCHUMANN,C. M., and J. F. HANCOCK, 1989 Paternal inheritance ofplastids in Medicago sat i va .Theor. Appl. Genet. 78: 863-866.SLATKIN,M., 1985 Rare alleles as indicators of gene flow. Evolution3 9 53-65.SOLTIS,D.E., P. S. SOLTISand B. G.MILLIGAN,1992 Intraspecific chlo-roplast DNA variation: systematic and phylogenetic implications,pp. 117-150 in MolecularSystematics of Plant s , edited byP. S. SOLTIS,D. E. SOLTISand J. J. DOYLE.Chapman & Hall,New York.STRAUSS,S. H., Y.-P. HONCand V.D. HIPKINS,1993 Highlevelsofpopulation differentiation for mitochondrial DNA haplotypes inPinus radia ta , murica ta ,and at t enuata . Theor. Appl. Genet. 86:

WAGNER,D. B., 1992 Nuclear, chloroplast, and mitochondrial DNApolymorphisms as biochemical markers in population geneticanalyses of forest trees. New For.6 373-390.WAGNER, D. B.,G.R. FURNIER,M. A. SAGHAI-MAROOF,S. M. WILLIAMS,B.P. DANCrKet a l . , 1987 Chloroplast DNApolymorphisms in lodge-pole and jack pines and their hybrids. Proc. Natl. Acad. Sci.USA

WAGNER,D.B.,D. R. GOVINDARAJU, C. W. YEATMANand J. A. PITEL,1989 Paternal chloroplast DNA inheritance in a diallel cross ofjack pine ( P i n u s b a n k s i a n a L a m b . ) .J. Hered. 80: 483-485.WAGNER,D. B.,J. DONG,M.R. CARLSON and A. D.YANCHUK,1991 Pa-Genet. 82: 510-514.ternal leakage of mitochondrial DNA in Pinus . Theor. Appl.WAGNER,D. B., W. L. NANCE,C. D. NELSON, T. LI,R. N. PATELet al . ,1992 Taxonomic patterns and inheritance of chloroplast DNAvariation in a survey ofPinus echinata , P inus el l i o t t i i , Pinus pa-lustris , and Pinus taeda .Can.J. For. Res. 22: 683-689.WANG,X-R,and A E. S m , 1990 Evolutionaryan- of Pinw densata(Masters), a putative Tertiary hybrid.2. A study using speaes-spedficchloroplast DNA markers. Theor. Appl. Genet 80: 641-647.W ~ G ,X.-R., and A. E. SZMIDT,1993 Hybridization and chloroplastDNA variation in a P i n u s species complex from Asia. Evolution(in press).WEIR,B. S., 1990 Genet ic Data Ana lysis: Methods for Discre te Popu-lat ion Genet ic Data.Sinauer Assoc., Sunderland, Mass.WHEELER,N. C., and R.P. GURIES,1982 Population structure, genicdiversity, and morphological variation in Pinus contortaDougl.Can. J. For. Res. 12: 595-606.

605-611.

84: 2097-2100.


8/8

1194 J. Dongand D. B. WagnerWHEELER,N . C.,and R.P. GURIES,1987 Aquantitativemeasure of substitutionvarygreatly among plant mitochondrial,chloroplast,introgression between lodgepole and jack pines. Can.J. Bot. 6 5 and nuclear DNAs. Proc.Natl.Acad. Sci. USA 84: 9054-9058.

1876-1885. WRIGHT,S. , 1951 The genetical structure of populations. Ann.WHITTEMORE,A.T., and B. A. S~HAAL,1991 Interspecific geneflow in Eugen. 15: 323-354.WOLFE,K. H ., W.-H. LI and P. M.SHARP, 1987 Rates of nucleotide Communicating editor: B. S. WEIRsympatric oaks. Proc. Natl. Acad. Sci. USA88: 2540-2544.

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