Diapause: Delaying the Developmental Clock in Response to a Changing Environment - Current Topics in Developmental Biology - page 232

Figure 8.6 Developmental growth of the killifish Austrofundulus limnaeus in relation to
diapause. Model of the two developmental trajectories in embryos of A. limnaeus. Dia-
pause is strictly associated with modifications of development. Early embryogenesis
normally occurs until 10-somite stage, without any difference between the two trajec-
tories. By the 18-somite stage, nondiapausing embryos (escape trajectory, diapause III)
differ morphologically from diapausing ones (diapause II trajectory). At the end of the
“escape” trajectory, the fully developed embryos enter obligate diapause III, which
occurs directly prior to hatching. Note the morphological differences between the
two developmental trajectories at level of trunk and cephalic development (red
arrowheads). Blue arrowhead: melanocytes; white arrowhead: eyes. Modified from
Podrabsky et al. (2010) with the permission of The Journal of Experimental Biology.
extremely resistant to both dehydratation and hypoxia still remain alive for
months in the complete absence of oxygen ( Podrabsky et al., 2010;
Podrabsky&Hand, 1999; Podrabsky,Menze, &Hand, 2012 ). Such tolerance
to anoxia, mostly exhibited by diapause II embryos, is maintained for several
days of postdiapause II development, providing a condition for which the
embryos develop actively but still being able to resist anoxia ( Podrabsky
et al., 2007 ).
Austrofundulus diapause seems to be overridden by steroid hormone. In
fact, nondiapausing embryos differ from diapausing ones in having higher
titers of estrogen (17- b -estradiol, E2) at 5/10-somites stage as well as in
the timing of morphological traits which do not develop until several days
after diapause (i.e., melanocytes, yolk vasculature, and otholite primordia).
Consistent with this observation, most diapausing embryos escape diapause
II when incubated with exogenous E2 ( Pri-Tal, Blue, Pau, & Podrabsky,
2011 ). Intriguingly, as in Austrofundulus , diapause seems to be maternally
primed in embryos of killifish Nothobranchius guentheri , in which diapause
is induced by “pheromonal-like” signals produced by adult fish since all