Ngo, H. N., T. Quang Phan, C. The Pham, T. Quang Nguyen, H. Van Nguyen, D. Trong Do, L. R. Gewiss, M. van Schingen-Khan & T. Ziegler

Distinct sexual dimorphism in a vulnerable lizard, Physignathus cocincinus, in Vietnam: an indirect cause for male-biased exploitation? pp. 254-262.

Abstract. Besides habitat destruction, unsustainable exploitation of wildlife can be a key threat to endangered reptiles. The Asian Water Dragon (Physignathus cocincinus), which is found in Vietnam and other Southeast-Asian countries, has been recently assessed as “Vulnerable” in the IUCN Red List due to severe human impacts. In particular, the species has been overexploited in Vietnam for local consumption and the international pet trade. We herein analyzed sexual dimorphism of P. cocincinus relating to alterations of sexual structure in exploited populations. A total of 90 adult Asian Water Dragons, including 50 females and 40 males, were examined with 15 morphometric and other external characters (e.g. coloration, crest size, tubercle form). There were significant inter-sexual differences in the dewlap with eye-catching colors, and development of nuchals, dorsal crest and tubercles on the neck and chin shields in males. Rensch’s rule favoring the male-biased pattern in some morphometrics of P. cocincinus (e.g. body length, head traits and weight) was also confirmed. Based on interviews and observations at restaurants, larger and heavier males were intensively harvested by hunters because of their higher suitability for food consumption and higher profits. We hypothesized that this apparent sexual dimorphism of P. cocincinus might indirectly cause a decrease in the number of male adults and impacting the demographic structure in disturbed populations due to selective exploitation. Thus, it needs to be further assessed to what extent wild populations can sustain male-biased harvest. In terms of conservation actions, we propose enhanced patrols to better protect and captive-breeding programs to re-stabilize wild populations of P. cocincinus.

Key words. Squamata, Agamidae, Asian Water Dragon, conservation, intentional exploitation, male-biased dimorphism, morphology, population.