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Figure 3.44
Serotonergic (yellow-green) and acetylated tubulin (red) immunoreactivity
in metamorphosing and early-juvenile-stage
Phestilla sibogae
. (A) Four hours into
metamorphosis: the five curled ampullary neurons (small arrowheads) appear to have retracted
from the epidermal surface, and deterioration of serotonergic axons (large arrowheads) is
evident. (B) Twenty-six hours into metamorphosis: the settled juvenile has elongated, and
there is no sign of an ASO. F, foot; CG, cerebral ganglia; CC, cerebral commissure.
Source
: From
Ruiz-Jones and Hadfield (2011)
.
modifications. Cuticle shedding is a motor behavior that, like any other behavior,
is expected to be controlled and regulated by the nervous system. However, in the
case of ecdysis behavior, Inka cells of an extraneural organ called the epitracheal
gland are usually considered initiators of ecdysis behavior. This has been disproved:
Inka cells in
Manduca sexta
, for example, are stimulated to produce pre-ecdysis-
triggering hormone (PETH) and ecdysis-triggering hormone (ETH) by a neuropep-
tide called corazonin, which is secreted by lateral brain neurons. Corazonin, both
in vivo
and
in vitro
, stimulates Inka cells to secrete both PETH and ETH (
Asuncion-
Uchi et al., 2010
;
Kim et al. 2004
). Responding to these hormones, the insect's brain
expresses the ETH receptor and secretes the neuropeptide eclosion hormone (EH).
The available evidence shows, as would be expected, that the first ecdysis signals the
start in the insect's brain.
Certainly, programming of the innate ecdysis behavior is more complex and
involves the activation of numerous neurons producing kinin, FMRFamides, EH,
crustacean cardioactive peptide (CCAP), myoinhibitory peptides (MIPs), and bursi-
con (
Truman, 2005
).
Metamorphosis in ascidians is essentially different from all other organisms.
While the transition of all other organisms from the larval stage to the adult stage
is associated with the development of an adult structure that is evolutionarily more
complex, adult ascidians are morphologically and behaviorally simpler organ-
isms. The free-swimming ascidian larva, with only approximately 2600 cells, has
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