EFFECT OF MICROGRAVITY AND HYPERGRAVITY ON EMBRYO AXIS ALIGNMENT DURING POSTENCYSTMENT EMBRYOGENESIS IN ARTEMIA-FRANCISCANA (ANOSTRACA)

Cysts of brine shrimp attached with a liquid adhesive to 12-mm diamete r glass coverslips in a syringe-type fluid processing apparatus were f lown aboard the NASA space shuttle Discovery, flight STS-60, from 3-11 February 1994, and were allowed to undergo postencystment embryogenes is and to hatch in microgravity. The shuttle flight and the ground-bas ed control coverslips with attached cysts were parallel to the earth's surface during incubation in salt water. Based on the position of the cyst shell crack in the attached cyst population, the ground-control nauplii emerged mostly upward. On the shuttle in microgravity, althoug h our method of detection of orientation would not reveal emergence to ward the coverslip, the ratio of the position of the cyst shell crack in the population after hatching best fit the predicted values of a ra ndom direction for nauplii emergence. Centrifugation on earth was then used to create hypergravity forces of up to 73 g during postencystmen t embryogenesis and hatching. The upward orientation of emerging naupl ii showed a high degree of correlation (r(2) = 98.8%) with a linear re lationship to the log of g, with 78.2% of the total hatching upward at 1 g and 91.0% hatching upward at 73 g.