Meeting Abstract
Development is a complex, seemingly fragile process, but embryos often tolerate large environmental fluctuations. For example, embryos of the sea slug Haminoea vesicula are laid on submerged substrata but can survive stranding out of water at low tide, despite being protected only by thin, gelatinous, ribbon-shaped egg masses. Previous work showed that H. vesicula embryos survive for days in egg ribbons that have lost 80% mass through dehydration, even when embryos are damaged to the point of dissociation. We examined two aspects of this remarkable ability. First, we hypothesized that stranded embryos would not survive to hatching. We simulated low tide by exposing egg ribbons to air and sun for 1 hr. Even in ribbons that lost 70% mass by dehydration, embryos still developed and hatched as veligers, many of which were malformed but some of which could still feed. Second, we hypothesized that three different structures — egg ribbon gel, egg envelopes, or cell membranes — could potentially protect embryos from increased salinity due to evaporation, by acting as diffusion barriers to water and salt. Fluorescein spread quickly through egg ribbon gel, indicating high permeability, so the gel likely does not prevent embryos from experiencing large salinity changes during drying. Embryos removed from the gel and put in hypersaline seawater shrank within 3 minutes, suggesting that neither envelopes nor cell membranes are significant permeability barriers on the timescale of exposure. Embryo volume remained greatly reduced over ≥ 1 hr, so cell volume regulation is insufficient to protect embryos from water loss. Thus, to survive stranding, H. vesicula embryos must tolerate large changes in the concentration of intracellular compounds, and may require regenerative abilities.
