Sexual dimorphism in the Vietnamese ground dragon (Physignathus cocincinus): an indirect cause of sexually selective hunting

19/12/2024

In addition to habitat destruction, unsustainable exploitation may be the main threat to reptiles. The Cocincinus cocincinus has recently been listed as “Vulnerable” on the IUCN Red List due to serious human impacts on its population due to commercial exploitation, domestic food and international ornamental farming. A team of scientists from the Institute of Genome Research, Institute of Ecology and Biological Resources, Phu Yen University, in collaboration with Cologne Zoo, Germany, conducted a survey and collected morphological data of the species in the wild. Through the analysis of sexual dimorphism of Cocincinus in different populations, sexual differences were noted, with males being larger and heavier than females. Sexual dimorphism was explained as an indirect cause leading to sexual selection in Cocincinus.

The Cocincinus cocincinus Cuvier, 1829, is widely distributed in Southeast Asia, and is recorded as an alien species in Hong Kong (China), Malaysia, Taiwan (China) and Florida, USA. It was recently listed as “Vulnerable” on the IUCN Red List, Appendix IIB of CITES, due to hunting and trade. Previous surveys of the impacted population in Thua Thien Hue noted a significant change in sex structure with a significant decrease in males during the hunting season. To explain the differences and changes in population structure, this study documented differences between males and females in morphological traits and explained the relationship to selective hunting trends.

Image of female (A) and male (B)

A total of 90 P. cocincinus individuals, including 50 females and 40 adult males, were measured for morphological characteristics. In addition, the team conducted interviews with hunters and several restaurants that recorded the sale and processing of the species, to collect information on hunting preferences and selling prices between males and females.

Analysis revealed distinct morphological differences between males and females. The crest and dorsal crest lengths are large in adult males, while they are relatively short in females. Males have purple undersides, while females have red and yellow.

Images of some dimorphic characteristics to identify females (A) and males (B)

The study noted body length (SVL), head and forearm size, and weight with larger values recorded in males, all supporting the male-biased model.

Sexual dimorphism, in which larger males are found, is explained by their advantage in competition among males for territory, food resources and mating opportunities. In addition, females tend to prefer males with optimal morphology for mating, and distinctive male traits such as coloration are prominent in the process of mating selection for females, and also provide an advantage in competing for mates.

Morphological comparison chart between male and female individuals of the Dragon species

Interviews with hunters and restaurants revealed that adult males are preferred by hunters and traders due to their higher selling prices in restaurants and pet stores. Based on this information, scientists suggest that male-biased sexual dimorphism in the Arowana may be an indirect factor influencing male abundance in the wild.

Changes in the population structure of P. cocincinus with a significant reduction in the number of adult males during the hunting season are one of the many negative consequences of human activity. Exploitation of wild animals causes a decrease in population size, genetic diversity, and can even lead to species extinction in the wild.

Source of published article:
https://www.salamandra-journal.com/index.php/contents/2024-vol-60/2160-ngo,-hn-,-t-quang-phan,-c-the-pham,-t-quang-nguyen,-h-van-nguyen,-d-trong-do,-lr-gewiss,-m-van-schingen-khan-t-ziegle r

Translated by Quoc Khanh
Link to Vietnamese version

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