Annual killifish embryo ecology

Embryo-environment interactions are of paramount importance during the
development of all organisms, and impacts during this period can echo far
into later stages of ontogeny. African annual fish of the genus
Nothobranchius live in temporary pools and their eggs survive the dry
season in the dry bottom substrate of the pools by entering a facultative
developmental arrest termed diapause. Uniquely among animals, the embryos
(encased in eggs) may enter diapause at three different developmental
stages. Such a system allows for the potential to employ different
regulation mechanisms for each diapause. We sampled multiple
Nothobranchius embryo banks across the progressing season, species and
populations. We present important baseline field data and examine the role
of environmental regulation in the embryonic development of this unique
system. We describe the course of embryo development in the wild and find
it to be very different from the typical development under laboratory
conditions. Development across the embryo banks was synchronized within
and across the sampled populations with all embryos entering diapause I
during the rainy season, and diapause II during the dry season. Asynchrony
occurred at transient phases of the habitat, during the process of habitat
desiccation and at the end of the dry season. Our findings reveal the
significance of considering wild environmental conditions in understanding
the importance of the serial character of the annual fish diapauses.