Meeting Abstract

96.4  Sunday, Jan. 6  Plasticity of egg mass architecture: effects of spatial oxygen gradients on the density and distribution of embryos PODOLSKY, R.D.; College of Charleston podolskyr@cofc.edu

The grouping of encapsulated embryos in dense clutches can impose several physical challenges on early development. For example, oxygen delivery to embryos can be limited by diffusion, creating a spatial gradient of increasing hypoxia from peripheral to central positions within a clutch. Such limitations are thought to constrain the thickness of egg masses and could alter other aspects of egg mass architecture related to the density or positioning of embryos. The balloon shaped egg masses of Melanochlamys diomedea, an opisthobranch mollusc that oviposits on the surface of tidal flats, have embryos distributed throughout a gel matrix. This architecture allows for fine-scale analysis of changes in embryo positioning in response to environmental conditions. I examined whether the radial distribution of embryos changes in parallel with the radial gradient of hypoxia, predicting that embryo densities would be lowest toward the center of masses. I also manipulated oxygenation levels experienced by adults to determine whether they effect plastic changes in the density or positioning of embryos in their masses. As predicted, embryo density declined toward the center of egg masses and decreased as an inverse function of adult oxygenation. Contrary to expectations, adult oxygenation levels did not generally alter the slope of embryo density as a function of radial position. These results suggest that adults tend to position their embryos away from more hypoxic positions but respond to changes in ambient oxygen by altering overall densities rather than the steepness of density gradients. Prior work found that in some populations, egg mass architecture is altered by changing the number of embryos packaged per capsule, but multi-embryo encapsulation was not apparent in the population used in this study.