Post Natal Lecithotroph: A New Age Class in the Ontogeny of Reptiles

Abstract

Lecithotrophic (yolk based) nutrition is a well-documented condition for the embryos of oviparous reptiles. However, the continuation of this nutritional state following hatching, here formally defined as postnatal lecithotrophy, has rarely been considered in reptile life history studies or in reptile nutritional strategies. Approximately 50% of the caloric value of yolk lipids may be conserved as a post hatching reserve for both growth and mobility in neonate North American tortoises. A preliminary experiment was designed to study if the metabolic dependence on residual yolk may be quantified and the duration of that dependence delimited. Baseline data from tortoise egg yolk established the lipid components available in the yolk prior to hatching. Analysis of blood plasma identified those lipid components present in adult tortoises, and finally, circulating blood from neonate tortoises was drawn at intervals to monitor the extent to which lipid components abundant in yolk continue to be utilized. Neonate tortoises subsisting on residual yolk had signifi- cantly higher plasma lipids than neonate tortoises that had been fed. All of the lipid fractions including total lipid, triacyl glycerol, phospholipid, cholesterol and cholesterol esters were signifi- cantly higher in fasted than in fed tortoises. Also there were significant differences in some of the individual fatty acids between fed and fasted neonates. Prior observations and inferences suggest that this nutritional stage may continue through the first six months following hatching. It may also be attenuated by a secondary conversion of yolk invested energy into fat. Field observations indicate that lack of rainfall and associated deficits in available forage may make newly emergent neonates in the western and central Mojave Desert almost entirely dependent on such reserves for their first half year of life. Post natal lecithotroph tortoises may be able to emerge into a dry September Mojave Desert landscape, disperse rapidly