Posthatching yolk energy in a lizard: utilization pattern and interclutch variation

Newly hatched green iguanas, Iguana iguana, retain a yolk mass which is similar in relative size (13.6% of body mass) and caloric content (6.87 kcal/g DM) to the posthatching yolks described in loggerhead turtles (Caretta caretta) and birds. The lipid: protein ratio in posthatching iguana yolk remains constant through depletion, which indicates that the nutrients are removed and utilized at the same rate. The yolk mass provides an important energy supplement for iguanas during the first month of life, when they must dig their way out from an underground nest, travel as much as several hundred meters from the nest site in search of older conspecifics, and eventually disperse to their own characteristic habitat, all before their hindgut fermentation system is fully operational. Interclutch variation in yolk size at hatching is significantly greater than variation in either body mass or length; this suggests that yolk provisioning in posthatching iguanas largely reflects the availability of nutrients to the mother beyond the minimum necessary for development of normally-sized young. Increased matenal investiment in eggs, as reflected in yolk size, may affect posthatching success of offspring through enhancement of growth rate as well as increased energy supply for activity. There appears to be substantial selection for maximization of juvenile growth rate and therefore body size at hatching, although in other reptiles, alternative strategies in egg provisioning may appear.