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The evolution of insect metamorphosis is one of the most important sagas in animal history, transforming small, obscure soil arthropods into a dominant terrestrial group that has profoundly shaped the evolution of terrestrial life. The evolution of flight initiated the trajectory towards metamorphosis, favoring enhanced differences between juvenile and adult stages. The initial step modified postembryonic development, resulting in the nymph-adult differences characteristic of hemimetabolous species. The second step was to complete metamorphosis, holometaboly, and occurred by profoundly altering embryogenesis to produce a larval stage, the nymph becoming the pupa to accommodate the deferred development needed to make the adult. These changing life history patterns were intimately linked to two hormonal systems, the ecdysteroids and the juvenile hormones (JH), which function in both embryonic and postembryonic domains and control the stage-specifying genes Krüppel homolog 1 (Kr-h1), broad and E93. The ecdysteroids induce and direct molting through the ecdysone receptor (EcR), a nuclear hormone receptor with numerous targets including a conserved transcription factor network, the 'Ashburner cascade', which translates features of the ecdysteroid peak into the different phases of the molt. With the evolution of metamorphosis, ecdysteroids acquired a metamorphic function that exploited the repressor capacity of the unliganded EcR, making it a hormone-controlled gateway for the tissue development preceding metamorphosis. JH directs ecdysteroid action, controlling Kr-h1 expression which in turn regulates the other stage-specifying genes. JH appears in basal insect groups as their embryos shift from growth and patterning to differentiation. As a major portion of embryogenesis was deferred to postembryonic life with the evolution of holometaboly, JH also acquired a potent role in regulating postembryonic growth and development. Details of its involvement in broad expression and E93 suppression have been modified as life cycles became more complex and likely underlie some of the changes seen in the shift from incomplete to complete metamorphosis.
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Name: Current biology : CB
Smittium (Harpellales, Kickxellomycotina) includes fungal symbionts associated with the digestive tracts of immature aquatic stages of various Diptera, including Chironomidae, Culicidae, Dixidae, Simu...
This autobiographical article describes the research career of Lynn M. Riddiford from its early beginnings in a summer program for high school students at Jackson Laboratory to the present "retirement...
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Juvenile hormone analog and insect growth regulator used to control insects by disrupting metamorphosis. Has been effective in controlling mosquito larvae.
The interdisciplinary science that studies evolutionary biology, including the origin and evolution of the major elements required for life, their processing in the interstellar medium and in protostellar systems. This field also includes the study of chemical evolution and the subsequent interactions between evolving biota and planetary evolution as well as the field of biology that deals with the study of extraterrestrial life.
Free-standing or supported light weight meshwork fabric made of cotton, silk, polyester or other material having openings too small to allow entry of mosquitoes or other insects, thereby protecting against INSECT BITES; INSECT STINGS, and insect-borne diseases.
Evolution at the molecular level of DNA sequences and proteins. (Rieger et al., Glossary of Genetics: Classical and Molecular, 5th ed)
A genus of insect in the mealybug family Pseudococcidae.
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