Sexual dimorphism in morphological traits and scaling relationships in two populations of Gallotia stehlini (Fam. Lacertidae: Squamata) from Gran Canaria

Abstract

Lizards of the genus Gallotia, endemic to the Canary Islands, show morphological and colouration varieties that are related to within island variation in orographic and climatic characteristics. This study examines sexual size dimorphism (SSD) within and between population variation in morphological traits, and scaling relationships in G. sthelini from a southwestern locality (Tasartico) and from another (Gáldar) in the northwest of Gran Canaria. Both sites differ in climate and vegetation traits, and we hypothesised that SSD should be manifested by males having relatively larger body traits than females and that hind limb lengths should be relatively larger in individuals from the more open habitat. Results showed that one-third of the largest lizards from both populations did not differ significantly either in snout-to-vent length (SVL) nor in trunk length (TRL), but overall males had significantly larger SVL and TRL than females. Multivariate analysis showed that head width (HW) and hind limb length (HLL) were significantly larger in individuals from Tasartico than in those of Gáldar. Hind limb length was the trait that contributed most to differentiate between populations and head parameters between males and females. In both populations head and body traits scaled to TRL, head width (HW) and head depth (HD) of males having a positive allometry, and fore limb length (FLL) and hind limb length (HLL) a negative one. In relation to head length (HL), females had significantly larger TRL and smaller head depths than males; lizards from Gáldar had significantly larger trunk length (TRL), but smaller HW and HLL than those of Tasartico. We outline the multiple factors that could affect the evolution of morphometric traits of each sex, taking into account the ecological features of the two zones.