Biology Reference
In-Depth Information
developmental changes in relation to adult diapause (
Zhan, Merlin, Boore, &
Reppert, 2011
), microarray analysis has revealed that insulin/IGF-1 signaling
(IIS) is downregulated indiapausingmigrants, suggesting that the activationof
the “anti-growth” Forkhead Box-O (FOXO) transcription factor, which is
antagonized by IIS signaling, might be a key molecule for inducing the dia-
pausing developmental switch (
Zhan et al., 2011
). Further evidence for an
insulin/IGFs role in diapause of some lepidopteran species (e.g.,
Samya cynthia
and
Pieris brassicae
) is provided by experiments in which the injections of
mammalian insulin into dormant pupae breaks diapause and stimulates a
resumption of “ECD-dependent” pupal growth (
Arpagaus, 1987; Wang,
Zheng, & Guo, 1986
). Lastly, insulin signaling has been proposed to play a
major role in directing reproductive diapause, in several insects (
Tatar and
Yin, 2001
). Reproductive diapause is a condition in which the energetically
expensive process of egg productionbymature adults is arrestedduringwinter
presumably inducing a more stress resistant physiology. Additional research
on the roles of insulin/IGF-type factors in both normal development (e.g.,
metamorphosis, larval growth, etc.) and in dormancy induction, utilizing
both vertebrate and invertebrate models will likely help identify additional
genetic and evolutionary mechanisms underlying seasonal adaptations.
9. SUMMARY AND PERSPECTIVE
Diapause is an alternative developmental pathway that blocks devel-
opmental growth by modifying the levels, or the timing, of developmental
hormones in response to environmental cues. The final result is a dormant
entity that is able to resist extremely low temperatures for several months.
Once the decision-making has been made, diapause trajectory drastically
modifies not only the physiology of diapausing stage, but also the larval
and pupal growth by altering either ECD signaling or other growth signals.
The developmental hormones that trigger diapause are also responsible for
the induction of seasonal morphs (polyphenism). Hence, diapause might
accelerate the evolution by genetic modifications of multiple polyphenic
traits that can be elicited upon exposure to the same, or temporally different,
environmental perturbations. Insights from species exhibiting multiple
polyphenic traits linked to diapause (i.e.,
B. mori
or
Araschnia levana
) will pro-
vide a framework for future research on this hypothesis and the inducibility
of alternative developmental pathways (developmental plasticity).
Another important issue is how photoperiodic changes are decoded and
transduced to modify hormonal signals and resulting in the activation of
