Endocrine control of metamorphosis explains the origin of the insect pupa
An invited review in Phil Trans R Soc B considers endocrine evidence in support of homology between juvenile stages of insects with complete and incomplete metamorphosis.
Image description: Alternative hypotheses for evolutionary relationships between holometabolous stages and those of a hemimetabolan ancestor (middle). Left: Holometabolous larvae arise by 'de-embryonization' (yellow) while hemimetabolous juvenile development is compressed to the pupa (orange). Right: Hemi- and holometabolous larvae hatch at an equal stage and the pupa is a modified late-stage hemimetabolous larva (green). Drawings: Martina Hajduskova (www.biographix.cz).
The 'miracle' of transforming caterpillars to beautiful butterflies has taunted thinkers since Aristotle. Particularly enigmatic is the origin of the pupa, a transitory stage between the caterpillar and the adult butterfly, which characterizes insects developing through 'complete metamorphosis' (holometaboly). The debate is on to this day. A theme issue of Philosophical Transactions of the Royal Society B published on August 26 (2019) confronts two historical concepts on the origin of complete metamorphosis. One hypothesis sees holometabolous insect larvae as early-hatching embryos whose discontinued development resumes at the pupa stage, which is said to comprise all juvenile stages of an 'incompletely' metamorphosing (hemimetabolous) ancestor. A competing view builds on a fact that insect larvae of both types leave their eggs at the same embryonic stage, and considers the pupa homologous to a late hemimetabolous larva from which it evolved by gradual modification. Our article advocates the latter hypothesis primarily based on recent discoveries of the hormonal control of insect development (https://royalsocietypublishing.org/doi/10.1098/rstb.2019.0064), which were in part achieved in our laboratory. (source: https://www.entu.cas.cz/en/news-events/news/4989/)
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