metamorphosis: one construct, many systems

Insect metamorphosis is the hormonally timed remodelling of the body between post-embryonic stages. In the holometabolous orders a feeding larva is torn down and rebuilt, inside a pupa, into a radically different winged adult, with juvenile hormone and ecdysteroids setting the timing of each switch. Truman and Riddiford's 1999 The origins of insect metamorphosis argues how the larval, pupal, and adult stages map onto ancestral embryonic phases and how this developmental reprogramming evolved. The referent is a staged transformation of body form under endocrine control, the same construct biologists recognise when a tadpole becomes a frog.[1][2]

Unit

The staged transformation of body form between larva and adult

Recovery means

Not applicable

Measured by

Tracked by stage transitions and by the hormone titres (juvenile hormone, ecdysteroids) that gate them

Amphibian metamorphosis is the same kind of event in a different lineage: a water-dwelling tadpole is remade into a terrestrial frog (tail resorbed, limbs grown, gut and nervous system rebuilt), driven here by thyroid hormone rather than ecdysteroids. Brown and Cai's 2007 Amphibian metamorphosis reviews how a single hormone signal orchestrates this coordinated, tissue-by-tissue transformation. It is the identical construct (a hormone-triggered post-embryonic rebuild into a new body form), realised through a different endocrine switch, which is why the two literatures share the word.[3]

Unit

The thyroid-driven remodelling of a larva into the adult form

Recovery means

Not applicable

Measured by

Followed by metamorphic stage (tail resorption, limb emergence) against thyroid-hormone level