Morphological and histological examination of polyphenic wing formation in the pea aphid <Emphasis Type="Italic">Acyrthosiphon pisum</Emphasis> (Hemiptera,Hexapoda) |
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Authors: | Asano Ishikawa Sakiko Hongo Toru Miura |
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Institution: | (1) Laboratory of Ecology and Genetics, Graduate School of Environmental Science, Hokkaido University, Sapporo 060-0810, Japan;(2) Department of Biology, Graduate School of Arts and Sciences, University of Tokyo, 3-8-1 Komaba, Meguro, Tokyo 153-8902, Japan |
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Abstract: | Aphids display divergent adult phenotypes, depending on environmental conditions experienced during their embyonic and nymphal
stages in their complex life cycles. The plastic developmental mode is an extreme case of phenotypic plasticity, so-called
“polyphenism”, in which discrete multiple phenotypes are produced based on a single genome. For example, winged and wingless
adult females are derived from a single genotype. However, the developmental mechanisms producing these polyphenic traits
according to the extrinsic stimuli, such as density conditions, still remain unknown. In this study, to analyze the developmental
processes underlying the wing polyphenism, we extensively observed and compared wing development in the winged and wingless
individuals in parthenogenetic generations of the aphid Acyrthosiphon pisum (Harris), using scanning electron microscopy and histological sectioning. At the first-instar stage, the wing primordia were
observed both in the future winged (W) and wingless (WL) nymphs. Developmental differences can be seen from the second-instar
stage, when wing primordia degenerate in the WL nymphs, while they develop and become more thickened in the W nymphs, suggesting
that the developmental programs should be launched prior to this stage. Furthermore, during the third- to fifth-instar stages,
wing buds and flight muscles were well developed in the W nymphs, while wing primordia completely disappeared in the WL ones.
In addition, the observation on the detailed developmental process of wing primordia during the third-instar W nymphs showed
that the wing buds become swollen especially at the basal part, even during the intermolt period. This was caused by the development
of wing epithelia under the cuticle of this instar nymph. Actually on the surface of the cuticle of wing-bud bases, there
were numerous furrows, which gradually expand during the intermolt period. The similar situation was also observed at the
forth-instar nymphs, in which the wings are formed in the complicated manner inside the wing pads. Furthermore, the developmental
process of flight muscles was also described in detail. These dynamic developmental differences between the wing morphs should
be regulated under the gene expression cascades that switch according to environmental stimuli. |
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Keywords: | Flight muscle Polyphenism Postembryonic development Wing bud Wing polymorphism |
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