pp.80–84

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Asiatic Herpetological Research, Vol. 11

An Investigation of the Morphometric Characteristics of Eggs of theChinese Alligator (Alligator sinensis)
WEI ZHI MENG1, XIAO BING WU1,* AND LU SHENG WU2
1Anhui Province Key Laboratory for Conservation and Exploitation of Biological Resource, Collegeof Life Science , Anhui Normal University, 1 East Beijing Road, Wuhu 241000, China,
2Division of Science and Technology, Jinan University, 601 Huangpu Avenue, Guangzhou 510632,China.
*Corresponding author E-mail: wuxb@mail.ahnu.edu.cn
Abstract.- In this study we analyzed morphometric intraspacific differences in the eggs of the Chinese alligator,Alligator sinensis, (egg mass, egg width and egg length). Data were collected for 1460 eggs from 40 clutches at theAnhui Research Center for Chinese Alligator Reproduction (ARCCAR). Our results found that the mean clutch size
was 36.5 eggs, mean egg mass per clutch was 41.9 g, and clutch mass was 1519.7 g. We generated three regression
equations relating to relationships among egg width, length and mass. The average of clutch size in 2004 was muchhigher than it was in 1985 as indicated by a two-sample t-test.
Keywords.- Egg shape index, egg length, egg width, egg mass, clutch size.

Introduction
Studies of the reproductive ecology of Alligator sinensis
are important for our understanding of its conservation
biology and status. Several studies about the reproductive ecology of Alligator sinensis are available andinclude information on egg incubation in captivity (Guand Zheng, 1983; Liang and Pan, 1990), nest excavation(Huang and Watanabe, 1986), the relationships between
egg hatching and environmental factors (Wang et al.,2000) and captive breeding (Cheng and Wang, 1984;Wang and Zhang, 2000; Xu et al., 1989). Egg characteristics are important when examining reproductive ecology, as has been illustrated in previous studies (Carielloet al., 2004; Du, 2003; Huang et al., 2003; Reese, 2000),
but little of this research has been devoted to Alligatorsinensis. We herein record data on egg characteristics of
the Chinese alligator in the ARCCAR, and analyze thesecharacteristics to investigate intraspecific differences,providing fundamental information for further study ofthe influence of egg shape on hatching rate and qualityof young alligators.

Materials and methods
Measurements of eggs.- A total 1460 eggs from 40
clutches were collected between 5 and 16 July 2004 at
the artificial breeding area of the ARCCAR. Eggs werecollected within 12 hours of laying and taken to a hatching room where their length and width were measured
with digital calipers (precision 0.01 mm). Egg mass was
taken using a scale (precision 0.1 g).

© 2008 by Asiatic Herpetological Research

Statistical analysis.- We analyzed the morphologicalcharacteristics of the eggs using the statistical software
SPSS (Version 10.0). Data on the distribution of egg
characteristics (including egg length, width, mass, egg
shape index [length/width], clutch size, clutch mass andclutch mean egg mass) were analyzed using descriptivestatistics. The coefficient of variation (SD/Mean) wasused to study variation in egg characteristics. Regression
analyses were used to examine the correlation amongegg width, length and mass. Hoyt (1979) put forward an
empirical formula:
W = KWXY2
where KW is the coefficient of mass, W is egg mass, X isegg length, and Y is egg width.

Results
Descriptive statistics of the morphological characteristics of the eggs of the Chinese alligator.- Table 1 provides descriptive statistics for the morphological characteristics of the eggs examined. From the frequency distributions of these morphological characteristics(Fig. 1), it is apparent that in most cases, egg length
ranges from 51.42 mm to 60.00 mm, egg width from32.49 mm to 37.51 mm, egg mass from 33.34 mm to48.33 mm, clutch mass from 1200 g to 1800 g, clutch
size from 30 to 45, and clutch mean egg mass from 35.0g to 47.5 g.
The egg of the Chinese alligator usually has theform of an elongate ellipse, although some eggs deviatedfrom this shape. From the frequency distribution of egg

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Table 1. Descriptive statistics of the morphological characteristics of the eggs of Alligator sinensis.
Maximum

Minimum

MeanSD

N

87.15

32.86

56.58

3.73

1460

Egg width (mm)

57.3

29.01

35.24

1.91460

Egg shape index

2.42

0.59

1.61

0.111460

Egg mass (g)

83.7

27

41.9

5.11460

Egg length (mm)Clutch size4615

36.5

6.2

40

Clutch mass (g)1978.4630.9

1519.7266.7

40

Clutch mean egg mass (g)

51.1

32.7

41.8

3.9

40

shape index, it was evident that in most cases, egg shapefalls between 1.50 and 1.72.
Intraspecific difference of egg morphological characteristics.- Since there were a high proportion of malformed eggs in four of the 40 clutches, only the 36
remaining clutches were analyzed. Figure 2 shows theCV (coefficient of variation) of egg morphological characteristics, indicating morphological variation among
eggs of the same clutch.
There were differences in variation among the morphological characteristics of the eggs laid by different
females. The CV of egg morphological characteristics
were calculated from Table 1, revealing that variation inegg mass (CV = 0.18) and clutch size (CV = 0.17) were
the greatest.
The correlations among the CV of egg morphological characteristics were analyzed using a Pearson correlation analysis (Table 2). Table 2 indicates that the CV ofthe egg shape index had a significant positive correlation
with the CV of egg width. The CV of egg mass had asignificant positive correlation with the CV of egg
length.
Correlations of egg length, egg width and egg mass.Data (including egg length, width and mass) collectedfrom 1445 eggs (malformed and broken eggs not included) were used to generate scatter plots. These plots indicated that both egg width and length had a positive correlation with mass, while length was negatively correlatTable 2. Pearson Correlations of CV of four egg morphological characteristics.

Egg shapeindex
Egg length
Egg width
Egg mass

Egg shapeindex

Egglength

EggwidthEggmass

1.000
0.424**
0.900**
0.287

0.424**
1.000
0.242
0.774**

0.900**
0.242
1.000
0.314

0.287
0.774**
0.314
1.000

** Correlation is significant at p < 0.01 (2-tailed).

ed with width. In order to obtain the exact correlation
between the two parameters, the influence of otherparameters was eliminated by using a partial correlation
analysis. The results showed that egg length had a significant positive linear relationship with egg mass(r = 0.875, p < 0.001); egg width had a significant positivelinear
relationshipwitheggmass(r = 0.856, p < 0.001); and egg width had a significant
negative linear relationship with egg length (r = -0.638,p < 0.001).
Linear regression analysis was used to analyze therelationships between egg width (Fig. 4), length, andmass (Fig. 3). Two regression equations were generated(1) W = -29.855 + 1.265 XL
R2 = 0.681, p < 0.001; df = 1443
(2) W = -53.078 + 2.699 XW
R2 = 0.637, p < 0.001; df = 1443.
Where W is egg mass (g), XL is egg length (mm), XW isegg width (mm).
We were able to approximate the original egg massfrom data about egg width and length using the twoequations.
In order to estimate egg mass (W) more exactly, weused the empirical formula given by Hoyt (1979) toderive another regression equation. From the scatterplots of egg mass and the volume (V) of the cube
approximately the volume of the egg (egg width x egg
width x egg length), it is evident that egg mass had a significant positively correlation with the volume of thiscube. Linear regression analysis (Fig. 5) yielded the following equation expressing the relationship between egg
mass and volume:(3) W = 1.656 + 0.00057V
R2 = 0.928, p < 0.001; df = 1443,
where V = XLXW2, so the final equation is:

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Figure 1. Frequency distributions of egg morphologicalcharacters of Alligator sinensis.

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p < 0.05). The data collected in 1985 were from the original parent generation captured from the wild, which is
no longer breeding, leaving the F1 generation to constitute the dominant portion of the breeding population(Wu et al., 1999, 2005). Many reproductive characteristics of squamate reptiles are fictile, clutch size being oneof them. In the wild, adult alligators must face pressuresrelating to natural selection potentially reducing theirfull reproductive potential, but in the ARCCAR, thenutrition of the alligators is regulated by artificial diets,
maximizing their reproductive potential. One way toquantify this potential is to examine egg morphologicalcharacteristics, which are directly influenced by nutrition.
Egg width and length data can be collected easily,
but data on egg mass are more difficult to obtain becausesome eggs might break while the female alligator protects her clutch, or if it is usurped by other females.
Furthermore, there is variation in egg mass during incubation (Wang and Zhang, 2000). In bird species examined in the wild, investigators have correlated egg
weight, width and length (Hoyt, 1979; Zhao and Ma,1997; Zhou, 1994) in order to calculate egg mass. The
regression equations (1), (2), and (4) established in thisstudy have been found to accurately estimate the original egg mass from data on egg width and length, providing an efficient means of measurement that can also beapplied to the mass of recently-hatched young alligators
if only the eggshell is available. This information subsequently be used to estimate the constitution of the young
alligators, gain basic information on wild populations,and develop a sound basis for investigation of wild populations. We conducted an analysis of variance test(ANOVA) to determine whether the egg masses predicted by the three equations differed from actual observations. The results showed no significant differences(F = 0.891, p > p0.05), illustrating that all three equations
can be used to calculate egg mass, although the accuracyof equation (3) (R2 = 0.928) is higher than that of theother two [(1) (R2 = 0.681); (2) (R2 = 0.637)].

(4) W = 1.656 + 0.00057XLXW2,
where W is egg mass (g), XL is egg length (mm) and XWis egg width (mm).

Discussion
In 1985 it was recorded that the clutch size of Chinese
Alligators at the ARCCAR, based on 29 clutches, was26.2 (SD = 3.9; n = 29) (Xu et al., 1989). Means ofclutch sizes in 1985 and 2004 were compared by a twosample t-test, revealing that the average clutch size in2004 was much higher than it was in 1985 (t = 7.77,

Figure 2. Coefficient of variation of egg morphologicalcharacteristics.

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Asiatic Herpetological Research, Vol. 11

Figure 3. The relationship between egg mass and length.

83

Figure 4. The relationship between egg mass and width.

tant variable in hatching rate, however, little research on
the relationship between egg shape and hatching rate has
been made, and is in need of further investigation.

Acknowledgments
This work was supported by National Natural Science
Foundation of China (NSFC, No. 30270213, 30470244),
the Foundation for Excellent Youth in Anhui Province(04043409) and Key Laboratory of Biotic Environment
and Ecological safety in Anhui Province.

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Figure 3. The relationship between egg mass and length.

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