全 文 ：生物多样性　第 8 卷 ,第 1 期 , 2000 年 2 月
CHINESE BIODIVERSITY　8(1):95～ 102 , February , 2000
Gene frequency distributions of Anthoxanthum alpinum
along the altitudinal gradients in Swiss Alps

ZHAO Gui_Fang 　　Francois Felber　　Philippe Kuepfer
Botanical I nstitute , University of Neuchatel , Chantemerle 18 , CH-2007 , Neuchatel , Switzerland.
Abstract:Anthoxanthum alpinum has a continuous distribution from the treeline(1700 m)to the summit ridges
(2830 m)in A rpette and Belalp of Valais , Swiss A lps.The highest and low est sites o f the transect differ by almost
1000 m in elevation , but only an average of 1.4 km apart.A significant clinal varia tion w as observed at three al-
lozyme loci(Px_1 , Got_2 and Mdh_1)on all three transects.I t suggests that gene flow among sub_popula tions may
be too weak to overcome the effects of natural selection in favor of adaptations to local conditions , and that tempera-
ture v ariables may function as major selective force in this case.
Key words:Anthoxanthum alpinum , clinal variation , enzyme polymorphism , altitudinal gradient , alpine plant
Introduction
Numerous descript ions of genetic polymorphism illust rate that the patterns of genetic diversi ty are
at least in part not random.Allele frequency clines at enzyme loci along ecogeog raphical g radients
have been regularly found (Clegg and Allard , 1972;Hamrick and Allard , 1972;Bergmann ,
1978;Bergmann and Gregorius , 1993;Nevo et al., 1979;Mit ton et al., 1980;Kahler et al.,
1980;Millar , 1983;Lumaret , 1984;Breitenbach_Dorfer et al., 1992).Allele f requency clines
w ere considered to be impo rtant in speciation (Endler , 1977), and w ere explained by historical
factors as postg lacial mig ration in Abies alba (Breitenbach_Dorfer et al., 1992)and recent con-
tact of formerly isolated populations of Pinus muricata (Millar , 1983).Allozymic variation in
Fagus sy lvat ica show ed to be related ei ther to climate or to geog raphy depending on the markers
used(Felber and Thiebaut , 1984;Cuguen et al., 1985).Action of selection w as also considered
to be probable for explaining genetic differentiation among the populations of Pinus ponderosa a-
long an altitude transect(M it ton et al., 1980)and Picea abies along similar climatic g radients
(Bergmann , 1978).
We are involved , since 1993 , in the project “ Environmental Changes and Modification in
the Sub_alpine_alpine Ecocline ” launched by Sw iss Priority Prog ram ENV IRONMENT .The ob-
jective of the project is to follow the evolut ion of the transition zone between upper limi t of the
sub_alpine forest and treeless alpine zone , with the help of ”phyto_indicator” of the modif ication
and the genetics of indicative species.
Anthoxanthum alpinum Löve &Löve(Poaceae)is a w idespread , perennial g rass species in
alpine regions , ex tending throughout the sub_alpine_alpine bel ts , ranging approximately from
1700 m to the highest ridgetops at our study sites in Swiss Alps in Valais.At lower altitude , A .
alpinum is replaced by a closely related species , A .odoratum (Felber , 1986).This broad dis-
tribution provides ideal opportuni ties to study genetic response of plant sub_populations to environ-
mental changes , because some important environmental conditions change rapidly w ith altitude.
Paper submit ted:August 27 , 1998;Received:August 27 , 1999
Present address:Department of Biology , Northw est Universi ty , Xi an　710069 , China
These conditions of ten inf luence opportunities for gene flow and selection (Waser , 1978;Galen
and Kevan ,1980;Galen et al., 1991).
The objective of the study is to investigate the variability of isozyme loci in A .alpinum
populations in the sub_alpine_alpine transi tio ns in order to seek genetic markers co rrelated wi th al-
titudinal gradients(space scale)that can be later used for monitoring genetic response to environ-
ment changes(t ime scale).
Materials and methods
Plant materials
A total of 18 diploid sub_populat ions of A .alpinum (2n=10)were sampled over three transects
on siliceous rocks in tw o different parts of Valais in the Sw iss Alps.The fi rst t ransect w as located
in Val d Arpette , in the ex treme eastern part of the Mont_Blanc massif.It w as a narrow side val-
ley , east_west oriented , located on the left side of the Rhone River , above M artigny.The second
transect w as located at Belalp , in the Aletsch region , in the southern part of the Aar massif.the
region of Belalp is a wide open lateral valley , no rth_south oriented , on the right side of the Rhone
River (Fig .1).
Fig .1　Two sample sites located in Sw iss Alps
Sampling w as alw ay s performed acco rding to an interval altitude of 1700 ～ 1900 m , 1900 ～
2100 m , 2100 ～ 2300 m , 2300 ～ 2500 m , 2500 ～ 2700 m , 2700 ～ 2900 m , depending on the dis-
tribution of the species in the location.In 1993 , nine sub_populations w ere collected on five si tes
on the transect of Arpet te and four on the t ransect of Belalp , respectively.In 1994 , 4 o ther sub_
populations were collected on the both t ransects to cover all altitudinal intervals.In addition , a
secondary t ransect , five sub_populations , was perfomed in Belalp in order to test preliminary re-
sults.Each sub_population consisted of 50 ～ 80 individuals collected at a distance of at least one
meter.The only exception is in Arpet te , 2780 m , where only a few individuals were found.The
plants collected were afterw ard cultivated in the experimental garden of the University of Neucha-
tel.
Electrophoresis
For the ext raction of soluble proteins , f resh leaf tissue of plants cult ivated in the experimental gar-
96 CHINESE BIODIVERS ITY　　　　　　　　　　　　　　　Vol.8
den w as collected and ground at 4℃ in 500 m l ex traction buffer (0.1 M Tris_HCL , pH 7.5 , 0.
1 M thiog lycolate sodium , 0.7%(w/v), polyethyleneglycol 20 000).The crude homogenates
w ere centrifuged at 1200 g fo r 20 minutes at 4℃.The supernatants were collected and then
stored at -80℃.
Electropho resis was carried out on horizontal starch gels (12%)and on vertical polyacry-
lamide gels(9%).Histidine_cit rate buffer sy stem w as used in the starch gels for electrophoresis
separation of malate dehydrogenases(Mdh), phosphog luconate dehydrogenases(Pgd), peroxi-
dases(Px), and alcohol dehydrogenases(Adh)(electrode buf fer:0.065 M L_Histidine/0.007
M Cit ric acid , pH 6.5;gel buf fer:0.0162 M L_Histidine/0.00175 M Cit ric acid , pH 6.5;mi-
g ration:20 min at 25 mA/100V , 4h at 60 mA/300V and 2h at 40 mA/200V).Px migrating to
the anode as well as mig rating to the cathode w as considered.Glycine_Tris buf fer system w as used
for elect rophoresis separation of glutamate oxaloacetate t ransaminases(Got)and tetrazolium oxy-
dases(To)in the vertical polyacry lamide gels(elect rode buffer:0.1 M Glycine /0.007 M Tris ,
pH 8.6;mig ration:3h at 160 mA/600V).
Table 1　Correlation analysis between allelic
frequencies and altitudinal gradients
Alleles N R
Adh_1a 18 -0.200
Adh_1b 18 0.139
Adh_1c 18 -0.035
P x_1 a 18 0.656＊＊
P x_1b 18 -0.656＊＊
CPx_1a 18 0.214
CPx_1b 18 0.214
Got_1a 18 -0.382
Got_1b 18 0.244
Got_1c 18 -0.001
Got_1d 18 0.222
Got_1e 18 -0.055
Got_2a 18 0.174
Got_2b 18 -0.392
Got_2c 18 0.321
Got_2c 15 0.673＊＊
Mdh_1 a 18 -0.203
Mdh_1 b 18 0.738＊＊＊
Mdh_1 c 18 -0.200
Pgd_1a 18 -0.215
Pgd_1b 18 0.347
Pgd_1c 18 -0.198
Pgd_2a 18 0.184
Pgd_2b 18 -0.150
Pgd_2c 18 -0.265
To_1a 18 0.131
To_1b 18 -0.131
To_2a 18 -0.162
To_2b 18 0.162
Note:＊＊=P<0.01;
＊＊＊=P<0.001
　　Enzyme staining for Mdh , Adh and Pgd was per-
formed according to the methods described by Wendel
and Weeden (1989).Px was stained by the use of the
method described by Lumaret(1982).To was stained
with the methods described by Valero (1980).In gen-
eral , subst rate concentrations had to be adjusted in re-
spect to the original methods.
Zymograms were analy sed acco rding to Zeroual_
Humbert_Droz(1985).When one locus coded fo r sever-
al alleles , the slow est_mig rating allele w as designated as
allele a , the others , in turn , were b , c , d up to e , ac-
cording to the number of alleles.
Results
Six enzyme systems including 11 loci were tested in the
study.Pearson correlation analy sis show ed that a signif-
icant co rrelation w as found between allelic frequencies of
Got_2c , Px_1 a and Mdh_1b and alti tudinal g radients
in all three t ransects studied(Table 1).
The Got polymorphism found in A .alpinum was
controlled by tw o gene loci.One of these loci(Got_1),
coding for the slow er mig rating Got zone in zymo-
g rams , exhibited five alleles in our study material , the
other gene locus(Got_2)was found to exhibit three dif-
ferent allelic types.At Got_2 locus , although allele a
and b were statistically heterogeneous , the deg ree of
differences f rom sub_population to sub_population was
small.Allele c increased w ith elevations in frequency
from 0.086 to 0.135 and 0.087 to 0.189 on tw o tran-
sects in Belalp_1 and Belalp_2 , respectively.However ,
the situation was very complicated on the t ransect in Ar-
97No.1　　　　ZHAO Gui_Fang et al:Gene frequency distributions of An thoxa nthum a lpinum in Sw iss Alps
pet te w here f requencies of allele c in the sub_population 2215 m and crest sub_populations , i.e.at
2620 m and 2780 m were very low (Fig.2).In order to verify this preliminary result , a sec-
ondary sub_population(at 2200 m)was sampled in Arpette in 1994 , and a similar result w as ob-
tained(Fig.2).The result indicates that there w as different genetic response to microhabitat con-
di tions at Got_2 locus.Furthermo re , it is w orthy to note that the allelic f requencies of Got_2c
tended to decrease in crest sub_populations in two locali ties.This may be due to environmental
pressure encountered in the crest sub_populations more than in the other ones.When 15 sub_pop-
ulations(except fo r three crest sub_populat ions)were pooled , a signif icant correlation(R =0.67 ,
P =0.006)betw een allele f requencies and altitude w as obtained(Table 1).x2 tests for deviation
from Hardy_Weinberg expectation at Got_2 w ere no t significant except for the sub_populations in
Arpette 2415 m and Belalp_2 2550 m where a significant deficiency of heterozygotes w as found ,
while the low er sub_populations at Arpet te(1830 m , 2015m and 2200 a)and at Belalp_2 (1815
m and 2030 m)and the higher sub_populations at Belalp_1(2575 m and 2830 m)showed no sig-
nif icant ex cess of heterozygotes(Table 2).
Table 2　Fixation indices for each transect
Populations Px_1 Got_2
Arpette
1830 0.518＊ -0.086
2015 0.541 -0.100
2200_a 0.330＊ -0.032
2200_b 0.564 0.112
2415 0.441＊ 0.190＊
2445 0.443＊ 0.164
2620 0.370＊ 0.104
2780 0.249 -0.133
Belalp_1
2020 0.553 0.206
2200 0.593 0.189
2405 0.727 0.046
2575 0.332＊ -0.081
2830 0.161 -0.169
Belalp_2
1815 0.478 -0.100
2030 0.753 -0.098
2230 0.406＊＊ 0.042
2430 0.217＊ 0.033
2550 0.363 0.260＊
＊=P<0.05 , ＊＊=P<0.01.
　　Anode peroxidase (Px_1), coding for the slower
mig rating Px zone in zymog rams , exhibited only tw o
alleles.A gradual allelic f requency changed along alti-
tude gradients w as observed on all three t ransects(R
=0.66 , P =0.003), although some dif ferences ex-
isted in three transects(Fig.3).x2 tests for deviation
f rom Hardy_Weinberg expectation at Px_1 show ed
that almost half of values show ed a signif icant def i-
ciency of heterozygotes(Table 2).This may suggest
that there were directional selection for these tw o al-
leles at Px_1 locus in two locali ties.
Mdh_1 , coding for the slow er migrating Mdh
zone in zymog rams , exhibited three alleles and was
highly polymorphic.Hybrid bands were of ten ex-
pressed ei ther betw een allele a and b , or betw een al-
lele b and c.Based on altitude , gene f requency of al-
lele b increased w ith elevations on the three t ransects
and showed a significant correlation with alti tude (R
=0.74 , P =0.0005)when 18 sub_populations w ere
pooled(Table 1 and Fig.4).
Discussion
Geographical variation of morphological and allozyme
characters in plant populations has been observed in
many species(Clausen et al., 1940;Grant and Hunter , 1962;Ward , 1969;Rochow , 1970;
Hamrick and allard , 1972;Schaal , 1975;Davies and Snaydon , 1976;Snaydon and Davies ,
1976;Waser , 1978;Silander , 1979;Silander and Antonovics , 1979;Chapin and Chapin ,
1981;Linhart et al., 1981;Meinzer et al., 1985;Waser and Price , 1985;Galen et al., 1991).
Allele f requency clines at enzyme loci associated wi th environmental variables suggest that varia-
tion may be maintained by natural selection.Bergmannn(1978)found co rrelation between allele
98 CHINESE BIODIVERS ITY　　　　　　　　　　　　　　　Vol.8
frequencies at acid phospho tase(Acph)locus and climatic pat terns along latitudinal and alti tudinal
g radients in Picea abies.Similar clines w ere also detected at phosphoglucomutase(Pgm)locus a-
long a steep elevational transect in Pinus ponderosa (M itton et al., 1980).Functional dif ferences
between allozymes(Breitenbach_Dorfer et al., 1992)as w ell as a correlat ion between temperature
Fig .2　Dist ribution of allelic f requency of Got-2c along three altitude t ransects
Fig.3　Dist ribution of allelic frequency of Px-1a along three altitude t ransects
Fig.4　Dist ribution of allelic frequency of Mdh-1b along three altitude t ransects
99No.1　　　　ZHAO Gui_Fang et al:Gene frequency distributions of An thoxa nthum a lpinum in Sw iss Alps
g radient and thermostability of allozymes(Bergmannn and Gregorius , 1993)at Idh_2 locus in A-
bies alba populations furtherly indicated the role of selection.In contrast , Baker et al., (1975)
and Schaal and Smith (1980)found no significant variation in allozyme frequencies among sub_
populations of Si lene mari tima and low levels of sub_population heterogeneity in Desmodium
nudi f lorum , respectively.Similarly , Oyama et al., (1993)also reported low levels of genet ic
v ariation at allozyme loci among Arabis serrata sub_populations along an altitudinal g radient in
Fuji Mountain in Japan , despite a g reat variation in mo rphological and ecological t raits under both
natural and controlled condit ions presented in plants of this species.
Elevational sub_populations of A .alpinum in our study sites in Sw iss Alps constitute a con-
tinuously conspecifics band that spans an average of 1.4 km g radient f rom shel tered timberline to
exposed alpine ridgetop.Despite the potential for stepw ise gene movement between these closely
adjacent sub_populations along these g radients , significant differentiation had been observed at
isozyme loci in this study.Moreover , Nei s measures of genetic distance also show ed that the sub_
populations in higher elevations did give higher values on all three transects and a signif icant cor-
relation had been found betw een genetic distance and differences of sub_population elevation(R =
0.54 , P=0.02).
In traditional view , the cline will be maintained by a balance betw een dispersal and selection
(Felsenstein , 1976).Any g radient in these allele f requencies , due to history or to w eak selection ,
w ill generate linkage disequilibrium in the cline , because tw o dissimilar populations are being
mixed(Li and Nei , 1974).This disequilibrium , interacting wi th selection at the primary cline ,
w ill in turn produce a step in allele frequency , and gene f low will be reduced.Furthermore , the
size of this step , at equilibrium , w ill be proportional to the g radient in allele f requency outside the
region of interest (Barton , 1979).Altitude corresponds to environmental gradients.Rapidly
changing environmental condi tions along these gradients could result in asynchronous f low ering ,
rest rict ing gene f low among the sub_populations.Therefore , the population dif ferentiation of A .
alpinum observed along all three alti tudinal t ransects in the study suggests that gene flow among
the sub_populat ions may be too weak to overcome the effects of natural selection in favor of adap-
tations to local conditions , and that temperature variables may function as an at least major selec-
tive force in this case.
The investigation gave insight about geographical variation of A.alpinum populations at
isozyme loci.Further reciprocal t ransplanting experiments and direct estimations of gene f low will
conduct in the same localities in o rder to understand the adaptive significance of genetic dif ferences
found here.
Acknowledgement
This study w as suppo rted by the Sw iss National Foundation for Scientific Research(Grant 50001-
35350)and fo rms a part of a Ph.D.thesis of G.F .Zhao to be presented at the University of
Neuchatel.
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Thesis , University of Neuchatel , Switzerland
阿尔卑斯山黄花茅(Anthoxanthum alpinum)
沿海拔梯度的基因频率分布
赵桂仿 　　F rancois Felber 　　Philippe Kuepfer)
(Botanical Institute , University of Neuchatel , Chantemerle 18 , CH_2007 , Neuchatel , Swi tzerland)
摘　要　在瑞士阿尔卑斯山的 2个定点样地 ,黄花茅从森林线(海拔 1700 m)到山顶(海拔
2830 m)呈连续分布 。在海拔梯度样带的最高和最低定样场所间的垂直距离差不多为 1000
m ,但 2个定样场所间相距仅仅 1.4 km 。在所研究的 3 个海拔梯度样带中 , 3个同工酶位点
(Px_1 , Got_2和 Mdh_1)被观察到有统计意义的倾群变异 。研究结果显示:沿海拔梯度样带
的亚居群间的基因流可能太弱不足以克服自然选择的影响 ,后者促使对局部环境的适应 。在
这种情况下 ,温度因子至少可能作为一种主要的自然选择力起作用。
关键词　阿尔卑斯山黄花茅 ,倾群变异 ,酶多态性 ,海拔梯度
(本文责任编辑:时意专)
102 CHINESE BIODIVERS ITY　　　　　　　　　　　　　　　Vol.8