Developmental post-Diapause II stasis in an annual killifish

 Annual killifish live in temporary pools which completely lose water  during the dry season. They reproduce through drought-resistant eggs  laid to the bottom substrate of the pools, thus surviving through the  dry season. The development of the killifish’s embryos is known to  involve three strictly defined stages, where the embryo may go dormant  and stop developmental progression. The system of the three facultative  diapauses – diapause I, II and III – was described in 1970’s and  remained firm since then. Here, we report on the potential of the  embryos of an African killifish species Nothobranchius furzeri Jubb to  enter an additional developmental stasis occurring in between the stages  defined to the diapause II and III. The stasis manifests as a full  developmental halt in a stage previously regarded as non-diapausing or  markedly slowed down development. It occurs under normal laboratory  incubation conditions and the embryos that entered the stasis are  capable of normal hatching after they exit the dormancy. The aim of the  study is to inform on the increased, cryptic complexity of the diapause  system while we discuss the possible reasons why the reported stasis  remained unnoticed for so long.