全 文 ：动物学报　52(2):250-255 , 2006
Acta Zoologica Sinica　　　　　 　
　 Received Aug.28 , 2005;accepted Nov.25 , 2005
　＊ This study w as funded by the gran ts from Nanjing Normal University and the local government of Zhejiang Province for the Key Discipline of
Zoology
＊＊Corresponding author.　E-mail:xji@mail.hz.zj.cn
　 2006动物学报 Acta Zoologica S inica
Sexual dimorphism and female reproduction in the multi-ocellated
racerunner Eremias multiocellata (Lacertidae)＊
LI Hong1 , JI Xiang1 , 2＊＊, QU Yan-Fu1 , GAO Jian-Fang1 , ZHANG Ling2
1.College of Life Sciences , Nanjing Normal University , Nanjing　210097 , Jiangsu , China
2.School of Life Sciences , Hangzhou No rmal College , Hangzhou　310036 , Zhejiang , China
Abstract　Reproductive success and morphological traits are intimately linked in lizards.We collected adult multi-ocellated
racerunners Eremias multiocellata from a population in Inner Mongolia(northern China)to quantify sexual dimorphism
and female reproductive characteristics of this poorly studied viviparous , lacertid lizard , testing fo r the prediction that the
evolution of sexual dimorphism is promoted by between-sex differences in reproductive success relating to adult mo rpho log-
ical traits.Adults are sexually dimorphic in head size but not in body size, with males having longer and wider heads than
do females of the same body leng th.Females ovulate from May to June and , under labora tory conditions , they giv e birth
to young from la te June to late July.Litter size ranges from two to four y oung.Litter mass is positively correlated with fe-
male SVL , but female SVL only explains a small portion(approxima tely 19%)of variation in litter mass.Both litter size
and neonate mass are not correlated with female SVL.Neonate mass is negatively correlated with relative fecundity(litter
size relative to female SVL), suggesting a trade-off between size and number of offspring in E.multiocellata.Overall ,
selective pressures towards large male and large females are bo th relatively w eak in E.multiocellata , and the evolution of
sexual dimorphism in head size results mainly from between-sex differences in reproductive success relating to adult head
size [ Acta Zoologica S inica 52 (2):250-255 , 2006] .
Key words　Reptilia , Lacer tid , Multi-ocellated racerunner , Eremias multiocellata , Sexual dimorphism , Female repro-
duction , Size-number trade-off
密点麻蜥的两性异形和雌性繁殖＊
李　宏1　计　翔1 , 2＊＊　屈彦福1　高建芳1　章　玲2
1.南京师范大学生命科学学院 , 南京 210097
2.杭州师范学院生命科学学院 , 杭州 310036
摘　要　蜥蜴繁殖成功率与其形态特征有密切的关系。作者在内蒙古乌拉特后旗采集密点麻蜥 (Eremias multio-
cellata), 定量研究该种形态特征的两性异形和雌体繁殖特征 , 检验与成体形态特征相关的两性繁殖成功率差异
是否能促进两性异形的进化。密点麻蜥成体个体大小无显著的两性差异 , 但头部大小两性差异显著;雄性个体
的头长和头宽均大于体长相同的雌性成体。繁殖雌体于五 、 六月份排卵;在实验室条件下 , 雌体在六月下旬至
七月下旬之间产仔。该种雌体年产单窝仔 , 每窝 2-4 仔。窝仔重与雌体体长呈正相关 , 但雌体体长仅能解释很
少一部分 (约 19%)窝仔重的变异。窝仔数和幼仔重均与雌体体长无关 。幼仔重与相对生育力 (相对于雌体体
长的窝仔数)呈显著的负相关 , 表明该种蜥蜴存在后代数量-大小之间的权衡。密点麻蜥雄体和雌体向较大体
型方向进化的选择压力均相对较弱 , 与成体头部大小相关的两性繁殖成功率的差异是导致该种蜥蜴头部大小两
性异形进化的主要原因 [ 动物学报 52 (2):250-255 , 2006] 。
关键词　爬行纲　蜥蜴科　密点麻蜥　两性异形　雌性繁殖　卵数量-大小权衡
　　The multi-ocellated racerunner Eremias mul tio-
cellata is a viviparous , lacertid lizard.The lizard
show s a preference for arid or semi-arid dist ricts cov-
ered by sparse vegetation , and its dist ributional range
covers Xinjiang , Qinghai , Inner Mongolia and w est-
ern Liaoning in no rthern China , Mongolia , eastern
Kirgizstan as w ell as southern Tuvin District in
Siberian Russia (Zhao and Adler , 1993;Zhao ,
1999).The food consists mainly of insects , their lar-
vae and spiders , and lizards are part icularly fond of
v arious beetles and these of ten form a large part of
their diet in the w ild(Zhao , 1999).
Although there is much anecdotal information on
diet , lit ter size , male reproductive cycle and morphol-
ogy of the species(Liu and Geng , 1995;Liu and Li ,
1995;Liu et al., 2005;Zhao , 1999), there is lit tle
quantitative data , especially on topics such as sexual
dimorphism and female reproduct ion.To date , there
has been no statistical analysis of sexual dimorphism
of E.multiocellata , although some empirical data on
morphological trait s are available (Zhao , 1999).
There has been no detailed examination of the repro-
ductive ecology of E.multiocellata , although inci-
dental information indicates that this viviparous lizard
produces a single lit ter of 1-4 young per breeding
season between June and August , with mating occur-
ring just prio r to ovulation in M ay (Zhao , 1999;Liu
et al., 2005).
To obtain more detailed info rmation , we study a
population of E.mult iocel lata in Wulatehouqi
(41°27′N , 106°59′E), Inner Mongolia , northern
China.Based on morphological measurements taken
for adult lizards collected f rom the field and females
g iving birth to young under the laboratory conditions ,
we present data on sexual dimorphism and female re-
production fo r the population , and make compar-
isons , where possible , w ith other species of lacertid
lizards to test fo r the prediction that the evolution of
sexual dimorphism is promoted by betw een-sex differ-
ences in reproduct ive success relating to adult mor-
phological traits (Cooper and Vit t , 1989;Hew s ,
1990;Mouton and Van Wyk , 1993).
1　Materials and methods
A total of 83 adult lizards [ SVL (snout-vent
leng th)>51 mm;Liu et al., 2005] were collected
by hand o r noose in mid-May 2005.All of these were
used for the collection of morphological data.Mea-
surements(to the nearest 0.01 mm)taken fo r each
lizard include SV L , tail leng th (TL), head length(HL , f rom the snout to the anterior edge of the tym-
panum), and head w idth(HW , taken at the posteri-
or end of the mandible).These measurements were
taken simply because comparable data on mo re than
ten species of other lizards have been available to us
(e.g., Ji et al., 1998 , 2002a , 2002b;Ji and Du ,
2000;Lin and Ji , 2000;Du and Ji , 2001).
After measurements w ere taken , tw enty-six
lizards w ere released to the site originally collected ,
and the remaining 60 lizards w ere transported to
Hangzhou , where females w ere individually palpated
to assess thei r reproductive conditions and w ere
marked by toe-clipping in a unique combination for
future identification.Ten males and 10 females w ith
yolking o r recently ovulated follicles w ere housed indi-
vidually 100×60×40 (leng th×w idth×height)cm3
plastic cages , the bo ttom of w hich was filled wi th 20
cm of fine sand and pieces of clay tiles.Mealw orms
(larvae of Tenebrio moli tor)and w ater enriched w ith
vitamins and minerals (Nekton-Rep , Nekton-prod-
uct)were provided ad libitum .These cages w ere
placed in a room where ambient temperatures w ere
never higher than 28℃and the room lights w ere pro-
grammed to create a 12 light∶12 dark cycle.A 250-W
light bulb , suspended at one end of each cage (20 cm
above the cage floo r), created a thermal gradient
f rom room temperatures to 55℃ for 12 h daily.
Lizards w ere exposed to a natural light cycle and some
direct sunlight , and w ere able to regulate body tem-
perature behavio rally during the pho tophase.
We checked the cages at least tw ice daily for
newborns , and immediately measured and weighed
them af ter bi rth.Females giving birth during the
same period were isolated from each other using 30×
20×20 cm3 cages so that new borns could be allocated
accurately to the mother.Postpartum females w ere
individually measured for SVL and weighed.We cal-
culated relat ive litter mass(RLM)by dividing li tter
mass by the postpartum female mass(Shine , 1992),
and relative fecundi ty by using the residuals derived
f rom the reg ression of lit ter size on maternal SVL(Olsson and Shine , 1997).
Five females producing abnormal lit ters w ith
various numbers of fully developed dead young , still-
borns , or unfert ilized egg s were excluded from statis-
tical analy ses.All data were tested fo r normality
(Kolmogorov-Smirnov test)and homogeneity of vari-
ances (Bart let t test), and loge-transformation was
performed when necessary to satisfy conditions for
parametric tests.Throughout this paper , values are
presented as mean ±1 standard error , and the signif-
icance level is set atα=0.05.
2　Results
The largest male and female w e recorded w ere
70.5 and 66.4 mm SV L , respect ively , but mean val-
ues for adul t SV L did not show sexual size dimor-
phism (unpaired tw o-tailed t-test , t =0.27 , df =
81 , P =0.79).ANCOVA with SVL as the covariate
revealed that the rates at w hich head length(F 1 , 79=
26.56 , P<0.0001)and head width (F 1 , 79 =9.46 ,
P<0.003)increased with increasing SVL were both
g reater in males than in females (Fig.1).ANOVA
analyses on residuals derived f rom the regressions of
2512 期 L I Hong et al.:Female reproduction of a lizard　　
HL and HW on SVL revealed that the sexes differed
in both head leng th (F 1 , 81=538.68 , P <0.0001)
and width (F 1 , 81 =309.73 , P <0.0001).Males
had longer and w ider heads than did females of the
same body leng th(Fig.1).
Fig.1 　Linear regressions of head length and head width
on SVL in adult E.multiocellata
S olid dots:males.Open dots:f emales.T he regression equations
are indicated in the figure.S ee text for statisti cal analyses.
　
Females larger than 55 mm SV L produced a sin-
g le lit ter per breeding season.Of the 30 females main-
tained in the laboratory , fourteen(approximately 47%)
had ovulated w hen they were collected , and the re-
maining 16 ovulated in the laboratory f rom mid-May
to early June.Females under the laborato ry condi-
tions g ave birth to young from late June to late July.
Lit ter size determined for 25 lit ters ranged from two
to four young (Table 1).Litter mass was positively
correlated with female SVL (r =0.44 , F1 , 23 =5.43 ,
P<0.03;Fig.2), whereas litter size(r=0.23 , F1 , 23
Table 1　Descriptive statistics of reproductive traits of female
E.multiocellata (n=25)
M ean Standard error Range
Snout-vent length(mm) 59.9 0.6 55.3-66.4
Pos tpartum body mass(g) 4.5 0.1 3.4-6.1
Lit ter size 3.0 0.2 2-4
Lit ter mass(g) 1.4 0.1 0.9-2.3
Neonate mass(g) 0.49 0.02 0.36-0.63
Relat ive lit ter mass 0.36 0.02 0.22-0.54
Fig.2 　Linear regression of litter mass on female SVL in
E.multiocellata
T he regression equation is indicated in the f igure.See text for sta-
ti stical analyses.
　
Fig.3 　The trade-off between size and number of off-
spring in E.multiocellata
Each data point represents one li tt er.T he regression equation is in-
dicated in the f igu re.See text for the definiti on of relat ive fecundity
and statist ical analyses.　
252 动　　物　　学　　报 52 卷　　　
=1.33 , P=0.26)and neonate mass(r=0.21 , F1 , 23=1.08 , P=0.31)were not.Neonate mass was nega-
tively correlated with relative fecundity (r =-0.50 ,
F1 , 23=7.63 , P <0.02;Fig.3).
3　Discussion
Adults of E.mult iocellata are sexually dimor-
phic in head size but not in body size (SVL).Head
size is larger in males than in females of the same
body size in E.mult iocel lata , which is consistent
w ith the results reported for numerous other species
of lacertid lizards w orldw ide (e.g., Braña , 1996;
Huang , 1998;Ji et al., 1998;Zhang and Ji , 2000;
Xu and Ji , 2003).Within lacertid lizards , however ,
the w ays through which sexual dimorphism in head
size arises seem to vary among species.For example ,
female Takydromus septentrionalis (northern grass
lizard)increasingly sacrifice head g row th for rapid
g row th in SVL to realize the g reater potential repro-
ductive output f rom a larger body size , whereas males
exhibit an increasingly rapid grow th of the head(Zhang and Ji , 2000).On the contrary , sexual di-
morphism in head size arises mainly because of the in-
creasingly rapid grow th of the head in males in
Eremias brenchleyi (upland racerunner;Xu and Ji ,
2003).The detailed w ay through which sexual di-
morphism in head size arises in E.multiocel lata is
currently unknown , because of the lack of morpho-
logical data on juveniles.However , as in other species
of lacertid lizards (Braña , 1996;Huang , 1998;
Zhang and Ji , 2000;Xu and Ji , 2003), adult males
do exhibi t an increasingly rapid grow th of head size in
E.mult iocel lata.
Fighting among st males for the possession of fe-
males never takes place in E.multiocellata .A male
w ishing to mate seizes a reproducing female in his
jaws by some part of her body and then maneuvers
until he has got hold of her by the f lank , usually near
the g roin.Clearly , the head size is important for male
E.mult iocel lata to increase their reproductive suc-
cess by subjugating females but not males.
Within the tw o species of Erem ias lizards we
have studied , female E.brenchleyi (mean RCM =
0.38;Ji et al., unpubl.data) produce heavier
clutches than do female E.mult iocellata (RLM =
0.36;Table 1)of the same body size (both length
and mass).Interestingly , adult females of the former
species have shorter and narrower heads than do adult
females of the latter species w hen variation in SVL is
removed using ANCOVA(P<0.01 for both HL and
HW).What can be inferred f rom this comparison is
that females w ith smaller heads have an increased po-
tential to produce larger clutches o r lit ters.Thus , our
data provide a support for the prediction that repro-
ductive output and morphological trait s are intimately
associated in female lizards (Vit t and Congdon ,
1978;Cooper and Vit t , 1989;Shine , 1992;Braña ,
1996).
Body size of E.mult iocellata shows no signif i-
cant SVL dimorphism , which is consistent w ith the
results reported fo r other lacertid lizards such as
T.septentrionalis (Ji et al., 1998;Zhang and Ji ,
2000), T.hsuehshanensis (Hsuehshan g rass lizard;
Huang , 1998)and E.brenchleyi (Xu and Ji , 2003)
w ithout field observations of male-male combat be-
havio r.Sexual size dimo rphism (SSD)is assumed to
evolve in lizards mainly because of betw een-sex differ-
ences in reproductive success relating to adult body
size (Cooper and Vitt , 1989;Hew s , 1990;Mouton
and Van Wyk , 1993).Theoretically , fecundity se-
lect ion favors large females and sexual selection favors
large males.The tw o selective pressures could cancel
each other out and , consequently , result in a lack of
SSD between males and females. In
E.multiocellata , how ever , selective pressure to-
wards increased male size is relatively low , because
the species lacks significant male-male combat behav-
io r.Moreover , E.mult iocel lata is unlike numerous
other lacertid lizards in that litter size (fecundity)is
no t co rrelated w ith female SVL (Liu et al., 2005)
and that female size(SV L)explains only a very small
portion(19%)of variation in li tter mass(reproduc-
tive output)in the species.These f indings suggest
that selective pressure tow ards increased female size is
also relatively low in E.mult iocel lata.Most proba-
bly , less pronounced male-male combat behavior as
well as less pronounced phy sical constraints f rom fe-
male size on fecundity and reproductive output are the
main reasons that explain w hy adult E.multiocellata
lack SSD.
Female E.multiocellata exhibit some flexibility
in timing of reproductive events but , in the field ,
most give birth in the w armest months(July and Au-
gust;Zhao , 1999;Liu et al., 2005).Females in
this study , how ever , gave birth from late June to late
July.Lizards in nature are subject to unpredictable
weather (and thus , basking opportuni ties)and food
availabili ty.However , under laboratory conditions ,
the unlimi ted food availability and the sui table ther-
mal environments allow developing embryos to be free
f rom the negative effects of the po tential const raints
imposed on pregnant females in nature.Thus , the
difference in birth date between offspring produced in
the laboratory and in the field , although no t surpris-
ing , adds evidence that envi ronmental factors may in-
fluence the rate of embryonic development in
viviparous lizards (Robert and Thompson , 2001;
Wapstra et al., 2004).
Our data confirm that female E.multiocellata
produce a sing le lit ter per breeding season (Zhao ,
2532 期 L I Hong et al.:Female reproduction of a lizard　　
1999;Liu et al., 2005).Under the laboratory con-
di tions , most adults can survive for at least two
years , w ith all adult females reproducing annually.
According ly , we conclude that E.multiocellata ex-
hibits i teropari ty.Large female E.multiocel lata on
average allocate more resources to reproduction than
do small females , although female SVL only explains
a small po rt ion of variation in litter mass.Females
w ith larger li tters produced smaller off spring , so
there must be is a trade-off between size and number
of offspring in E.mult iocellata.Based on available
data , such a trade-of f can be detected in some species
[ e.g., Lacerta agi lis (sand lizard);Olsson and
Shine , 1997;T.septentrionalis;Du et al., 2005b]
but no t in o thers [ e.g., Podarcis muralis (com-
mon w all lizard);Ji and Braña , 2000 ] .As in
T.septentrional is (Ji et al., 1998;Du et al.,
2005a)and P.muralis(Ji and Braña , 2000), varia-
tion in offspring size as a function of female SV L w as
not found in E.multiocellata.This result coupled
w ith the size-number trade-of f presumably add evi-
dence fo r the prediction f rom the classical model
(Smith and Fretwell , 1974)that the t rade-off be-
tween size and number of of fspring should lead to the
evolution of optimally sized offspring.
Acknowledgements　We are g rateful to DING Guo-
Hua , GUO Li , HAN Jun , LU Hong-Liang and
ZHANG Jian-Long fo r thei r help during the research.
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2552 期 L I Hong et al.:Female reproduction of a lizard