Vol. 42 No. 2, 2003
Skewed Sex Ratio of the Chinese Green Tree Viper, Trimeresurus stejnegeri stejnegeri, at Tsaochiao, Taiwan
Shiuang Wang, Hua-Ching Lin and Ming-Chung Tu*
Department of Biology, National Taiwan Normal University, Taipei, Taiwan 116
Shiuang Wang, Hua-Ching Lin and Ming-Chung Tu (2003)
Preliminary collecting of adult Chinese green tree vipers, Trimeresurus
stejnegeri stejnegeri, in Tsaochiao, northwestern Taiwan, yielded a
male-biased sample. According to the sex ratio theory, a skewed sex
ratio is unlikely at birth, and the above results may thus reflect
sampling bias or differential mortality after birth. We collected
litters of neonates of this viviparous snake from a broader area over a
longer period to examine causes of such numerical dominance of males in
the adult sample. We collected 23 gravid females from the Tsaochiao
area in 3 consecutive reproductive seasons and obtained 50 male and 40
female neonates. The sex ratio at birth was not significantly biased.
We marked and released a total of 169 male and 79 female T. s.
stejnegeri. Marked snakes were recaptured 940 times. Regardless of
season, time of day, transect, or sample area, we always encountered
more males than females. Thus, sampling bias did not likely account for
this skewed sex ratio. In the adult sample, the ratio of males was
greatest in the largest size class, and this suggests that females are
subjected to higher mortality. We thus hypothesize that the skewed sex
ratio observed in overall adult samples of T. s. stejnegeri reflects
such differential mortalities between sexes that are probably derived
from a higher cost of reproduction in females.
Key words: Sex ratio, Mortality, Habitat, Activity, Snake.
*Correspondence: Tel: 886-2-29336234 ext. 321. Fax: 886-2-29312904. E-mail: email@example.com