Embryonic growth and mobilization of energy and material in oviposited eggs of the red-necked keelback snake, Rhabdophis tigrinus lateralis.

We used the red-necked keelback (Rhabdophis tigrinus lateralis) as a model animal to study embryonic growth and mobilization of energy and material in oviposited snake eggs. Females (N=12) laid eggs between late May and early June. Eggs were incubated at 30 (+/-0.3) degrees C. One egg from each clutch was dissected at five-day intervals starting at oviposition. Incubation length averaged 27.9 days. Three phases of embryonic growth or yolk depletion could be detected in this study. The first phase, between oviposition and Day 10, was one of minimal transfer of energy and material from yolk to embryo. The second phase, between Day 10 and Day 22-23, was characterized by increasingly rapid embryonic growth and yolk depletion. The third phase, between Day 22-23 and hatching, was characterized by a gradual reduction in embryonic growth and yolk depletion. Approximately 73.6% of dry mass, 50.0% of non-polar lipids and 57.8% of energy were transferred from egg to embryo during incubation. Embryos withdrew mineral from the eggshell mainly during the last quarter of incubation. Our data show that oviposition does not coincide with the onset of rapid embryonic growth in oviparous species of squamate reptiles that are positioned midway within the oviparity-viviparity continuum, and that the greater conversion efficiencies of energy and material from egg to hatchling in snakes can be mainly attributed to their lower energetic costs of embryonic development and greater residual yolk sizes.