Sexual Dimorphism and Age Structure in a Population of Tylototriton verrucosus (Amphibia: Salamandridae) from the Himalayan Region

We measured 17 morphometric characters of 38 females and 50 males from one of the largest known populations of the Himalayan Newt, T. verrucosus, located in the Darjeeling District of West Bengal, India. To evaluate the proximate causes of sexual dimorphism, we determined individual age by skeletochronology. At the breeding site, females were significantly longer and heavier than males and had larger heads and longer limbs. Despite their smaller size, males had bigger cloacae and higher tails. Females were, on average, 2.5 years older than males, and about 26% of them were older than the oldest male sampled. In both sexes, snout-vent length increases with age. Males were smaller than females independent of age: the difference in the mean age at maturity (2.5 for males and 3.2 for females) is the main source of the observed sexual size dimorphism. With the effects of body size statistically removed, males show proportionally longer forelimbs, longer tails, and a different head shape. The results are discussed in the light of life history and differences in mating behavior between the sexes.