68.11 Jan. 7 Plasticity of embryo encapsulation and density in intertidal egg masses PODOLSKY, R.D.; College of Charleston, Grice Marine Lab email@example.com
Reproduction in intertidal habitats can expose offspring to variable and extreme physical conditions, particularly when embryos are contained in benthic clutches. The high density of embryos in clutches can exacerbate the negative effects of intertidal conditions, especially with regard to the supply of oxygen to embryos. For this reason, gel in clutches is thought to function in spacing embryos and reducing oxygen limitation. The opisthobranch mollusc Melanochlamys diomedea deposits gelatinous egg masses in shallow pools on soft-sediment tidal flats. Embryos are enclosed in small capsules, which are contained within a tube that spirals through the gel matrix. Comparisons from three populations of M. diomedea showed population differences in embryo densities, a pattern that is explained partly by differences in the number of embryos per capsule. These populations also experience differences in physical conditions that could lead to different degrees of oxygen limitation. In the laboratory, I manipulated temperature and oxygen conditions experienced by adults from a source population with almost exclusive single-embryo encapsulation (and, consequently, relatively low embryo densities). Under certain temperature-oxygen conditions, adults were induced to incorporate a greater number of multi-embryo capsules per egg mass (leading to higher embryo densities). Because adults produce relatively few large masses in a season, egg masses with greater embryo densities allow higher reproductive output. Adults of M. diomedea appear able to manipulate the density of embryos in response to ambient conditions. These preliminary results indicate that plastic responses by adults that alter risks for embryos can involve not only the location or timing of reproduction but also the design of brooding structures.