REYNOLDS, Julie A; HAND, Steven C; Louisiana State University; Louisiana State University: Biochemical Indicators of Metabolic Poise During Development and Diapause of Cricket Embryos
Developing insect embryos must minimize water loss yet maintain adequate oxygen diffusion across the chorion. This presents a paradox because modifications to the egg structure that restrict water loss may also limit oxygen diffusion and create a hypoxic environment for the embryo. We have observed embryos of the Southern ground cricket, Allonemobius socius, to have unusually high AMP/ATP and low ATP/ADP ratios during early embryogenesis, which suggests embryos may be hypoxic early in development. AMP/ATP is 2.7-fold higher in embryos incubated in moist cheesecloth for 72 h post-oviposition compared to embryos similarly incubated for 168 h; ATP/ADP increases 82% over the same period. In addition 72 h embryos have high levels of lactate compared to 168 h embryos (1.17 and 0.193 nmol µg DNA-1 respectively). Superfusing 72 h embryos with moist, O2 enriched air (40% O2) partially relieves the hypoxic state as lactate is reduced by 35% and ATP/ADP is increased by 50%. Surprisingly, increasing environmental PO2 does not significantly reduce AMP/ATP of 72 h embryos. The metabolic profile of embryos that enter diapause is similar to that of embryos that do not arrest development which suggests the unusual energy status is not a feature of diapause. Taken together these data provide biochemical evidence that A. socius embryos are hypoxic early in development. A change in chorion permeability that occurs approximately 120 h post-oviposition appears to relieve hypoxia and may explain the ontogenetic decrease in lactate and the increase in ATP/ADP. However, the atypical set points for biochemical indicators of metabolic poise appear to be an ontogenetic feature that is only partially explained by oxygen availability. (Sigma Xi and Orthoptera Society GIAR to JAR and DARPA N00173-01-1-G011 to SCH).
