Influence of temperature and darkness on embryonic diapause termination in dormant Artemia cysts that have never been desiccated.
Environmental cues for embryonic diapause termination (EDT) were investigated in the laboratory-produced encysted dormant embryos of the brine shrimp, Artemia franciscana. The cysts were spawned and kept throughout in a 2% sea salt solution. They were activated by various temperatures of the temperate zones or by continuous dark condition (DD), resulting in a state of EDT, and were thereafter able to resume their subsequent development and hatch under appropriate conditions. The level of EDT was conveniently assayed by a hatch test observed within 2 days at 28 degrees C under continuous light condition (LL). A cold treatment of the newly spawned dormant cysts, at 4 degrees C under DD for more than 100 days, resulted in more than 95% hatch of the dormant cysts. Similar treatments of the dormant cysts but at room temperature or 28 degrees C led to significantly different results (30-40% hatch). Almost all the residual non-hatched cysts derived from the above could hatch after an additional cold treatment (at 4 degrees C under DD for about 100 days). This might prove to be latent partial bivoltine in Artemia. Meanwhile, a rearing condition (28 degrees C under LL) induced the newly spawned cysts to hatch scatteredly at and after 1 month, resulting in 22% cumulative hatch on the 92nd day after spawning. When the newly spawned dormant cysts were pretreated at 28 degrees C under DD for 5 or 14 days and then reared at 28 degrees C under LL, the cumulative hatch significantly increased (60%). These results are discussed with respect to probable diapause regulator(s) involved in EDT.
Nambu
Ziro
Z
Biology, Department of Clinical Pathophysiology, School of Health Sciences, University of Occupational and Environmental Health, Japan, Kitakyushu, Fukuoka, Japan. zf-nambu@health.uoeh-u.ac.jp
Tanaka
Shin
S
Nambu
Fumiko
F
Nakano
Masahiro
M
D000818:Animals; D001156:Artemia / Q000196:embryology*; D003624:Darkness; D003890:Desiccation; D013696:Temperature