9.3 Friday, Jan. 4 Delay of hatching in the sand dollar Echinarachnius parma in response to reduced salinity ARMSTRONG, AF*; BLACKBURN, HN; ALLEN, JD; University of California, Davis; College of William and Mary; College of William and Mary email@example.com
Hatching plasticity occurs in response to a wide range of stimuli across many animal taxa including annelids, arthropods, flatworms, molluscs, and chordates. Despite the prominence and long history of echinoderms in developmental biology, environmentally-cued hatching plasticity has only been described in a single species: the sand dollar Echinarachnius parma. Following our initial observations of hatching plasticity, we conducted detailed experiments on the effects of temperature and salinity on hatching plasticity in three male/female pairs. We tested how temperature, salinity, and their interaction affect time-to and stage-at hatching. While all factors had a significant effect, salinity had the largest effect on hatching plasticity in E. parma. Embryos of E. parma delayed their time to hatching more than two-fold in response to a salinity reduction from 32 psu to 26 psu while maintaining an otherwise normal developmental schedule. Embryos that experienced the greatest delay in hatching time emerged from the fertilization envelope as 4-arm pluteus larvae rather than hatching as blastulae or early gastrulae. We observed high variability in hatching time and stage both within and among clutches, suggesting intraspecific variation in developmental responses to salinity. A delay in hatching may provide embryos short-term protection from a harmful environment. The simplicity of the manipulation and the reliability of the results suggest that hatching plasticity may be a common occurrence in sand dollar development. The wealth of data on echinoid development, combined with the molecular and genetic tools available, may make sand dollars and sea urchins a valuable model system for future studies of the mechanisms underlying hatching plasticity.