Biology Reference
In-Depth Information
vertebrate diapause using the killifish embryo as an example where diapause is an envi-
ronmentally determined developmental switch analogous to that observed in lepidop-
teran dormancy. Based on the examples discussed here, we propose that the complex
physiological responses leading to diapause might evolve quickly by relatively limited
genetic changes in the regulation of hormonal signals that program normal develop-
mental transitions.
1. INTRODUCTION
Diapause is an “actively induced” dormancy that blocks developmen-
tal growth of an organism in anticipation of a major harsh seasonal change,
such as winter. The diapausing phase is genetically specified, but it is elicited
not in response to developmental cues, but by reliable environmental signals,
such as photoperiod and temperature, that are perceived during an earlier
developmental stage (
Saunders, Steel, Vafopoulou, & Lewis, 2002
). Hence,
diapause profoundly influences the trajectory of holometabolous growth
without causing any functional developmental aberration in the final adult
form, although as we will describe, there is some developmental plasticity
associated with diapause that is frequently manifested as seasonal poly-
phenisms in adult morphologies (
Saunders et al., 2002
).
While induction of diapause is genetically encoded and requires input from
the endocrine system, exiting the dormant stage also requires a “genetically
established” period of chilling to enable reactivation of development
when a more optimal environment (spring) is encountered (
Denlinger,
Yocum, & Rinehart, 2012; Lee & Denlinger, 1991
). For instance, diapausing
pupae of
Samia cynthia
must spend 3-5 months below 4
Cpriortobreaking
diapause, while dormant embryos of
Bombyx mori
require about 2 months
below 5
C(
Horie, Kanda, & Mochida, 2000; Nakamura et al., 2011;
Suzuki, Fujita, & Miya, 1983
) before reactivating the maturation process.
Without the cold period, dormancy cannot be broken (
Denlinger et al., 2012
).
Diapausing organisms are extremely resistant to low temperatures by
either undergoing supercooling or freezing, often in the presence of biolog-
ically produced cyroprotectorants (
Denlinger et al., 2012; Hahn &
Denlinger, 2010; Lee & Denlinger, 1991
). As an example, pupae of the pap-
ilionid
Papilio machaon
can resist freezing up to
25
C but even after freez-
30
C, they still remain alive for months (
Shimada, 1980
). Likewise,
larvae of the lymantrid
Gymnaephora groenlandica
undergo supercooling until
ing at
7
C, but they can survive freezing down to
70
C(
Kukal, Serianni, &
