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

in Amphibia-Reptilia
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Total body size for arboreal vipers is normally biased toward small males and larger females. We evaluated sexual dimorphism in adult and sub-adult Trimeresurus macrops, a small, arboreal green pit viper commonly found in Southeast Asia, but severely understudied. We evaluated morphological characters of 139 adult T. macrops obtained 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 female T. 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 in T. macrops. Sexually dimorphic characters in T. macrops may have evolved through intraspecific resource partitioning.

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

in Amphibia-Reptilia



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    Adult male T. macrops (A) with a visible post ocular stripe and adult female T. macrops (B) with no visible post ocular stripe. Photo credit: Andrew Brown. This figure is published in color in the online version.

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    The relationship between (A) SVL and HL of male (n=42) and female (n=51), and between (B) SVL and HW of male (n=42) and female (n=51) T. macrops. Linear regression fits and associated r2 values are displayed in each sub-figure.

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    The relationship between (A) SMI and HL of male (n=42) and female (n=51), and between (B) SMI and HW of male (n=42) and female (n=51) T. macrops. Linear regression fits and associated r2 values are displayed in each sub-figure.

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    Biplot of (A) first and second and (B) second and third principal component axes for males (M) and females (F), with their explained proportion of variance, showing the intersex variation of morphometric variables.

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