Sexual Size Dimorphism and Reproductive Cycle of the Little File Snake Acrochordus granulatus in Phangnga Bay, Thailand

Sansareeya Wangkulangkul,^a* Kumthorn Thirakhupt^a and Harold K. Voris^b

ABSTRACT: A total of 119 little file snakes (Acrochordus granulatus), collected at Phangnga Bay from February 2002 to August 2003, were studied. The snakes were divided into four groups according to their sex and reproductive stage: 23 juvenile males, 19 adult males, 32 juvenile females and 45 adult females. T-test and discriminant function analysis were used to analyze the data on sexual size dimorphism. Significant differences (t-test, p0.05) in 11 of 14 morphological characters were found between the sexes of adult snakes. Weight, head length, head width, distance between eyes, snout to gape length, mouth width, snout to vent length, neck girth, body girth and tail girth were larger in adult females than in adult males while vent width was greater in males. In juvenile snakes, only two morphological characters, mouth width and vent length, were significantly different. Results from discriminant function analysis yielded an equation for predicting the sex of adult little file snakes with the original grouped case correctly classified at 98.3%.
      Reproductive data indicated that the breeding season of A. granulatus begins in July. From July to December, the testicular volume increased, surpassing that observed from January to June. Following an increase in size of follicles to vitellogenesis, ovulation was observed in September. The embryos were first observed in January and young snakes of about 360 - 400 mm snout to vent length were first caught in June.

Download PDF

a Department of Biology, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand.
b Department of Zoology, The Field Museum of Natural History, 1400 S. Lake Shore Drive, Chicago, IL 60605, USA.

* Corresponding author, E-mail: wsansareeya@hotmail.com

Received 19 Jan 2005
Accepted 27 May 2005