Variation of clutch size in meadow viper (Vipera ursinii macrops) from eastern Montenegro

Abstract

Variation in a few reproductive traits (i.e. clutch size, female body size after parturition, and hatchling body length), as well as correlations between female body size and clutch characteristics such as number of newborns, average offspring body length and mass were studied during two consecutive years in local population of Vipera ursinii macrops from Bjelasica Mountain in Northeastern Montenegro. Average snout-vent length (SVL) in gravid females was estimated as 392.50 ± 11.59 mm with range from 340 – 457 mm. Average clutch size (calculated as the number of viable and stillborn offspring) was 6 (5.5 ± 0.69) and varied from 2 – 9 offspring per family. General positive correlation was detected between female body mass/clutch size, female body length /clutch size, female body mass/ overall clutch mass and female body length /clutch size. Relationship between mother’s body size and clutch size appeared to be significant, as was tested by Pearson’s product moment correlation between clutch size and mother’s SVL, as well as between mother’s body mass measured immediately after capture (BMAC; r = 0.64, p = 0.026 and r = 0.82, p = 0.0009, respectively). Percent of stillborn offspring was more frequent in large clutches. But, results of Spearman rank-correlation showed that, while larger females are heavier in pregnancy and produce more offspring, there is no impact on number of stillborn offspring by either mother’s body size or clutch size. Differences between two consecutive years in average body size of gravid females and in their clutch size were not detected (Mann Whitney U Test, p = 0.372 for both female SVL and BMAC; p = 0.417 for clutch size). Sex ratio in families varied from 0 to 1, with average value of 0.43 ± 0.32. Differences between years in offspring sex ratio per clutch were not significant (Man-Whitney U test: Z = -0.24, p = 0.81).