Reproductive cycle of the sand lizard (Lacerta agilis) in its southwesternrange

The reproductive cycle of Lacerta agilis was studied in the Pyrenees at the southwestern boundary of the species range. The activity period is short ( about 4.5 months). Males attain sexual maturity at smaller sizes than femal es and show mixed type spermatogenesis and spring spermiogenesis. Vitelloge nesis in females is rapid (45 days for the whole population) with a long pe riod of oviductal retention. Clutches are laid at the beginning of summer. During the reproductive period males mobilise reserves during the mating ac tivities. Females deplete more fat reserves but later in the season than ma les and they are at their lowest after egg production. In both sexes. energ y resources are mobilised from the fat bodies and also from the liver and t he proximal part of the tail. Clutch size increases with female size but al so depends on other factors. The short activity period does not appear to a ffect the reproductive cycle of this species. The gonad cycles and clutch t raits do not show substantial differences from other European populations, perhaps with the exception of slight variation in the timing of reproductiv e events and, to a lesser extent, clutch frequency. This evidence strongly suggests that the limited southwestern range of Lacerta agilis not due to e nvironmental constraints but to very recent colonization.