Sexual dimorphism of tropical green pit viper Trimeresurus (Cryptelytrops) macrops in Northeast Thailand

Abstract

Total body size for arboreal vipers is normally biased toward small males and larger females. We evaluated sexual dimorphism in adult and sub-adultTrimeresurus macrops, a small, arboreal green pit viper commonly found in Southeast Asia, but severely understudied. We evaluated morphological characters of 139 adultT. macropsobtained by active and opportunistic searches at Sakaerat Biosphere Reserve in northeast Thailand, from May 2012 to October 2014. We compared 7 external characters including residual index (Ri) and scaled mass index (SMI) between male and femaleT. macrops. Body length measurements and mass differed between males and females. Females had greater snout-vent length, body mass and head length and width, while males had greater tail lengths. A postocular stripe was always present on males, but never on females. Male head size was negatively correlated with SMI, which may reveal intersexual competition inT. macrops. Sexually dimorphic characters inT. macropsmay have evolved through intraspecific resource partitioning.

Seeing wildlife behavior in a new way: Novel utilization of computer vision for focal reptile videography behavior study

“…Research permissions for this separate project did not allow for direct disturbance of animals or their habitats, thus, we were not able to capture big‐eyed pit vipers for morphometric measurements (mass, length, fecundity). Sex was determined through external characteristics, primarily presence (male) or absence (female) of a white postocular stripe, which has been observed for this species at the site by Strine et al (2015). The primary author visually estimated big‐eyed pit viper size; if big‐eyed pit vipers appeared longer than 400 mm they were classified as adults (derived from Strine et al [2015], who observed sexual maturity for the smallest T. macrops in their study to be at 450 mm), if smaller they were classified as juveniles; no exact size was estimated, however.…”

“…Sex was determined through external characteristics, primarily presence (male) or absence (female) of a white postocular stripe, which has been observed for this species at the site by Strine et al (2015). The primary author visually estimated big‐eyed pit viper size; if big‐eyed pit vipers appeared longer than 400 mm they were classified as adults (derived from Strine et al [2015], who observed sexual maturity for the smallest T. macrops in their study to be at 450 mm), if smaller they were classified as juveniles; no exact size was estimated, however. All 3 female T. macrops observed in 2020 were found at the Sakaerat Environmental Research Station, which is within the core zone of the biosphere reserve (Figure 1).…”

Snakes: Slithering from Sensory Physiology to Cognition

“…The males may use it to locate females (Coupe, 2002), or it may be used as a tag, indicating areas where food is abundant (Clark, 2007). Social behavior has also been observed in captive indian pythons (Python morulus) and wild big-eyed pitvipers (Trimeresurus macrops), but nothing is known about frequency of such behavior in these species in the wild (Barker et al, 1979;Barnes et al, 2019).…”