Ametabolic insects

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Ametabolic insects summarizes the insect groups, including the other Hexapoda , which were formerly classified as insects , in which the young animal differs from the adult animal, the imago (sexually mature, adult insect) only on the basis of its degree of sexual maturity . In contrast, in hemimetabolic insects, the developmental stages ( larvae , often called nymphs here , if no larval organs of their own) and the imagines can be distinguished by the presence or absence of wings . In the third group, the holometabolic insects, there is also a pupal stage between the larvae and the imaginal stage , in which the body structure is radically reshaped.

In the past, the Ametabola, synonymous expressions are " urine insects " or "apterygota", were also understood as a systematic group. In contrast to the holometabolic insects, the ametabolic insects, like the hemimetabolic insects, are not a natural related group according to more recent findings. The ametabolic development is the original course of development within the hexapods (Hexapoda), so it is a primordial characteristic common to the combined groups, a symplesiomorphy .

Ametabola as a taxon

Many pioneers of entomology understood the groups, which can be distinguished according to the course of development, as systematic units or taxa . William Elford Leach compared "Metabolia" and "Ametabolia" in 1815. Hermann Burmeister differentiated in the "Handbuch der Entomologie" (1832) "Insecta metabola" and "Insecta ametabola", from 1835 he divided the "Insecta hemimetabola" from these. After the emergence of cladistics or phylogenetic systematics in the 1950s, these categories were no longer used as systematic units. Today, of the "Ametabola" only the fish and the rock jumpers are counted among the insects. Of these, the fish are more closely related to the winged insects than to the rock jumpers.

Ametabolic development

Ametabolic development is development without metamorphosis . There are numerous larval stages, larvae and adults look alike; it is often difficult to identify sexually mature animals with certainty. In some, but not all, fish and rock jumpers, sexually mature animals also continue to shed their skin regularly, for example in the furnace fish ( Thermobia domestica ). The development has been poorly researched in relation to the holometabolic and the hemimetabolic, only a few studies are available on the oven fish. Here too, development is hormonally controlled, with the level and ratio of ecdysone and juvenile hormone probably playing a decisive role. In the furnace fish, for example, the appearance of scales on the cuticle in the third larval stage has been attributed to a drop in the level of the juvenile hormone.

Before the actual larval stages, ametabolic insects have a mobile stage that lives for several days, the so-called prolarve. This is also present in the hemimetabolic insects, but often short-lived and immobile. According to a widespread hypothesis, the larvae of the holometabols can be traced back to them, which accordingly would not be homologous to the nymphs of the ametabolic and hemimetabolic.

supporting documents

  1. ^ Hickmann, Roberts, Larson, l'Anson, Eisenhour: Zoologie . 13th edition, Pearson Studium, 2008, ISBN 978-3-8273-7265-9 , p. 640 Google Books
  2. ↑ Nikita Julievich Kluge (2010): Circumscriptional names of higher taxa in Hexapoda . Bionomina 1: 15-55.
  3. ^ Hermann Burmeister: Handbook of Entomology . Berlin: G. Reimer; from vol. 2: Theod. Chr. Friedr. Enslin, 1832–1855 full text source
  4. ↑ Alessandro Minelli, Carlo Brena, Gianluca Deflorian, Diego Maruzzo, Giuseppe Fusco (2006): From embryo to adult - beyond the conventional periodization of arthropod development . Development Genes and Evolution 216: 373-383, doi : 10.1007 / s00427-006-0075-6
  5. ↑ JAL Watson (1964): Moulting and reproduction in the adult firebrat Thermobia domestica (Packard) (Thysanura, Lepismatidae). I. The moulting cycle and its control . Journal of insect physology 10 (2): 305-317.
  6. ↑ Aniruddha Mitra (2013): Cinderella's new shoes - how and why insects remodel their bodies between life stages . Current Science vol. 104, no. 8: 128-1036.
  7. ↑ James W. Truman & Lynn M. Riddiford (2002): Endocrine insight into the evolution of metamorphosis in insects . Annual Revue of Entomology 47: 467-500.
  8. ↑ James W. Truman & Lynn M. Riddiford (1999): The origins of insect metamorphosis . Nature vol. 401: 447-452.