I

Asiatic Herpetological Research

June 1995

Vol. 6, pp. 157-160

Research on the Sex Sensitive Period During the Incubation of ChineseAlligator Eggs

ZHENG-DONG ZHANG
Anhui Research Center of Chinese Alligator Reproduction, Xuanzhou, Anhui, China
Abstract. -The sex of Chinese Alligators (Alligator sinensis) is determined by the temperature thatincubating eggs are exposed to. There is a sex sensitive period between the 14th and 27th day of incubation.

Eggs treated at temperatures above 34° C produce males.

Key words: Reptilia, Crocodylia, Alligatoridae, Alligator sinensis, China, incubation, sex sensitive period.

Introduction

two-year study (1988-1989) are reported
here.

generally understood that the sex
distinction of the majority of reptiles(including crocodiles and alligators) isdetermined by the environmental
temperature during incubation. We haveconducted several experiments on theincubation of Chinese Alligator (AlligatorIt issinensis) eggs at different temperatures.

At present, there has not been a study
which reports the existence of the "sexperiod" in the incubation ofalligator eggs. Ferguson (1982) reported on
the sex exchange during the entire period ofincubation for Alligator mississipiensis eggs
at different temperatures. In regard to the"sex sensitive period" of Alligator
mississipiensis (Fergusion called it"temperature sensitive period"), it issensitive

believed that the sex determination occurs in
the period between the second and third
week of incubation. In 1988, we visited theUnited States and learned that an approach

Materials and Methods

The eggs for the experiment wereselected from captive reproduction at theAnhui Research Center. It is imperative toknow the exact time when the eggs are laid.
The time difference for the laying of theexperimental eggs should not be more than 6hours, nor remain in the natural environment
over 12 hours. It is essential that the entire
brood be collected immediately and then theeggs divided into separate groups to behatched under artificial temperature control.

Each experimental group is made up
with a corresponding number of eggs fromeach pre-determined brood to erase theinfluence which may originate from thedifferent broods.
In 1988, three experimental groups were

had been in progress to jointly study the"sex sensitive period" of Alligator
mississipiensis by American and British

organized: 88-1, 88-2 and 88-3 together
with a control group. The time to undergo
the high temperature treatment was prearranged with Group 88-1 from the 2nd toLondon using more accurate

the 15th day after the eggs were laid, Groupmeans. Obviously such an approach in
China still remains blank at the time of88-2 from the 16th to the 29th day, andGroup 88-3 from the 30th to the 43rd day.
All the high temperature treatments wereconducted in a constant temperature box.
For the rest of the time, each group wastaken to the incubation room under thescientists inwriting.

For the purpose of initiating an approach
whether there really exists a"sex sensitive period" during Chinese
Alligator egg incubation, the Anhui
Research Center of Chinese Alligator
Reproduction has been conducting
experimental studies since 1988 in search of
to determine

factual understanding.

The results of the© 1995 by Asiatic Herpetological Researchnormaltemperature.

Theaveragetemperature received by the groups at thevarious stages are listed in Table 1 (Thetemperature appearing on the list and all listshereafter is in Centigrade).

Vol. 6, p. 158

TABLE 1.
1988.

Asiatic Herpetological Research

April 1995

The incubation temperature of experimental groups and control group at various time periods inApril 1995

Asiatic Herpetological ResearchVol. 6, p. 159

TABLE 3. The incubation results, growth comparisons and sex ratio of the 1988 groups (weight in gramsand length in centimeters).

Vol. 6, p. 160

Asiatic Herpetological Research

36±0.5°C to the temperature environment(The data relative to this test is not presentedhere). Therefore", the range of temperature
control at this stage for Group 88-1, in fact,
reached the high temperature limit. In
comparison, the average temperature applied
to Group 88-2, which was raised 0.5°C
higher than that of Group 88-1, safety could
be ensured at that time threshold.

From data gathered from various groups
in 1988 on the growth of young alligators, itindicated that although among the threegroups, the weight of young alligators inGroup 88-2 was the largest, those in Group88-1 had the smallest weight. However,after 90 days (Nov. 25), the youngalligators of Group 88- 1 overtook the othertwo groups, and the weight of Group 88-2
became smallest among the three groups.
Such condition was maintained until theconclusion of the experiment. The average
length of the young alligators in the threegroups showed a similar phenomenon (SeeTable

April 1995

Based on the incubation results of young
alligators in various

groups as well as thecause of mortality in the first 10 months, it
was determined that the physical conditionof young alligators in Groups 89-1 to 89-9
was considerably weak, corresponding withthe result obtained in 1988. Comparatively
speaking, those in Group 89-10 proved tobe better. The materials relative to their sex
distinction revealed that the time thresholdfor high temperature in this group has
somewhat deviated from the "sex sensitiveperiod". Therefore, during the time of the"sex sensitive period", the unisexual
offspring that we obtained from treatment ofartificial
temperature control wereconsiderably weak. At the initial stage ofgrowth, they require particular care.
Direct study has discovered that there
exist some other factors which
influence the "sex sensitive period" of themay

Chinese Alligator. At present, we are deepin our research on this field.

This suggests that the young
whichwere under the treatment ofalligators,3).

Literature Cited

the special temperature at the "sex sensitiveperiod", have become comparatively weak.

CHENG, B. H., Z. H. HUA, B. H. LI.

The sex proportion of Group 88-1, 88-2
and the control group revealed that Group88-1 was almost the same as the sex

Publishing House, Hefei, 1st edition. (In Chinese).

proportions of wild Chinese Alligators
which we have studied (M:F=5:1). The
time threshold of high temperature treatmentfor Group 88-2 was just at the "sex sensitiveperiod". All of them were males. Those in
the control group showed sex differences

somewhere between the other two groups.
The cause of the latter condition is still
unknown (Table 3).
In the experimental test in 1989, the sex
proportion from the various groups wasmuch beyond expectation. It provided theunderstanding that the time threshold for the"sex sensitive period" in the incubation of
the Chinese Alligator is quite wide in range.
Direct study on experiments and Group 88-2
pointed out that the time threshold must befrom the 14th to the 27th day during the timeof incubation.

1985.

[Chinese Alligator]. Anhui Science and Technology

FERGUSON, M. W. J. AND T. JOANEN.

1982.

Temperature of egg incubation determines sex inAlligator mississipiensis. Nature 296:850-853.

WANG, P. C.

1989. [Progress of studies onenvironmental sex determination in reptiles]. Acta

Ecologica Sinica 9(l):84-90. (In Chinese).