SEXUAL DIMORPHISM IN LACERTID LIZARDS - MALE HEAD INCREASE VS FEMALE ABDOMEN INCREASE

Lacertid lizards exhibit sexual dimorphism in size corrected values fo r abdomen (always larger in females) and head (larger in males) length s. Relative abdomen length increased with SVL in females but did not i n males. The mean abdomen/head ratio for juvenile lizards (sexes poole d) was lower than that of females but did not differ from that of male s in any of the studied species. Therefore, the ontogenetic developmen t of the main body segments (abdomen and head) was isometric in male l izards, whereas female abdomen exhibited positive allometric growth. S tandardized independent contrasts (Felsenstein's method) of female abd omen to head ratio and of the slope of the regression of clutch size o n SVL explained a significant amount of variation in sexual size dimor phism in a stepwise multiple regression model. The fact that sexual si ze dimorphism was best explained by variables related to female reprod uctive investment, together with the ontogenetic trajectories of body segments suggest that sexual size dimorphism results mainly from varia tion in female size. Despite the suggested prominent role of selection on female body size in determining the outcome of size dimorphism, th ere was also evidence of selection for increased body size in males, w hich were the largest sex in species with low selective pressure towar ds increased female size (constant clutch size or low fecundity slope over size). Evidence for intersexual food (prey size) partitioning was weaker than expected from the widespread dimorphism in body size or r elative head size found among lacertid lizards. Furthermore, the devel opment of ''body segments'' was in some instances inconsistent with th e competitive hypothesis, the largest sex having relatively smaller tr ophic structures.