SEXUAL DIMORPHISM AND SEXING OF MEDITERRANEAN COLUBRIDS BASED ON EXTERNAL CHARACTERISTICS

Sexual dimorphism was studied in seven colubrid species living in the Mediterranean area of the Iberian Peninsula. Six variables of external morphology were considered: numbers of ventral and subcaudal scales, snout-vent and tail lengths, body and tail surface in a cross section close to the vent, and certain ratios of these variables. To determine which traits enable us to distinguish between the sexes, we used a st epwise discriminant analysis. The ventral and subcaudal scales, becaus e their numbers are fixed at birth, were the best predictors of the se x of a randomly-chosen specimen. Using the number of ventral scales an d certain ratios, we correctly identified the sex in all individuals o f Elaphe scalaris and Natrix maura, nearly 100% of the individuals of Coluber hippocrepis and Natrix natrix, and almost 95% of Coronella gir ondica and Macroprotodon cucullatus. The method did not work with Malp olon monspessulanus, which is sexually monomorphic in the characterist ics used here.