Ontogenetic changes in bone compactness in male and female Nile monitors (Varanus niloticus)

The compactness of bone tissue was measured in the shaft of the femur, tibi a and fibula in 390 male and female Nile monitors Varanus niloticus from th ree distinct regions of Sahelian Africa. In males, bone compactness increas es during ontogeny in the three bones. Conversely, in females, it tends to decrease in the femur and, to a lesser extent, the tibia, but not in the fi bula. In addition to this long-term trend, gravid females have lower femora l compactness than mature non-gravid ones. Moreover, important differences are noticeable between local samples, indicating that the variation in bone compactness during ontogeny is a flexible or even a facultative process. H istological observations reveal the existence of an extensive remodelling b y resorption and reconstruction on the walls of the marrow cavity in the fe mur and tibia, and the complete absence of Haversian substitution. It is co ncluded from these data that: (1) during ovogenesis, female Nile monitors r ecycle skeletal calcium through cortical resorption in certain bones, if th e calcium supply from food is not enough; (2) this remodelling process is n ot balanced, which creates a long-term tendency towards a deficit in recons tructive bone, and a consecutive decrease in the compactness of the skeleta l elements involved. The comparative and functional aspects of these result s are discussed.