Diapause: Delaying the Developmental Clock in Response to a Changing Environment - Current Topics in Developmental Biology - page 227

developmental pathway has proceeded past a critical point ( Koch &
B¨ckmann 1987 ). Diapause-bound morphs of Araschnia also differ in other
aspects of developmental growth. The prorsa morph is larger and exhibits a
different wing shape, heavier thorax, and smaller abdomen than levana ,
reflecting their differential dispersal rates ( Fric & Konviˇka, 2002 ). More-
over, diapause trajectory is strictly linked to the duration of fifth larval instar
with the levana morph having a delayed development ( Windig & Lammar,
1999 ). A simplified model of Araschnia seasonal morphs and diapause is
shown in Fig. 8.4 .
A diapause-linked diphenism also occurs in B. mori in which a moth lay-
ing diapausing embryos exhibits a greater number of dark scales on the wings
(autumnal morphs) than those laying developing eggs (spring-summer mor-
phs) and the diapausing embryos are darker with a thicker chorion than
directly developing ones ( Tsurumaki, Ishiguro, & Yamanaka, 1999 ). “Non-
diapause” pupae develop as autumnal or intermediate moths (instead of sum-
mer moths) upon implantation, during the early fifth larval instar, of the
Brain-SOG complexes of “diapause” larvae. In contrast, no morph shifting
is provoked when autumn moths (“diapause”) receive the Brain-SOG com-
plexes of fifth instar larvae set to develop into summer morph (“nondiapaus-
ing”) ( Yamanaka, Tsurumaki, & Endo, 2000 ). Such effects are due to DH
since its injections into young “nondiapause” pupae induce them to develop

Figure 8.4 Hormonal control of morphs in Araschnia levana. In short

days of autumn, the last larval instar develops into a dark diapausing pupa (diapause
trajectory) carrying numerous tubercles, upon failure of the pupal ECD signaling. After
chilling, the dormant pupa breaks diapause by eliciting a pulse of ECD, which is delayed
because of dormancy. This

“ diapause-bound ”

pupal pulse of ECD induces pupae to develop into
levana morphs. In contrast, the light pigmented nondiapausing pupae (development
trajectory) elicit a precocious pulse of ECD which induces the progression through
metamorphosis. Hence, the developing pupa ecloses as prorsa butterfly morph. ImD,
imaginal wing discs. Wings modified from Nijhout (2003) with the permission of John
Wiley & Sons Ltd.

“ delayed ”