Transduction of high-density signals across generations in aphid wing polyphenism

Wing polyphenism in aphids represents an outstanding example of adaptive phenotypic plasticity. During summer, parthenogenic mother aphids alter the developmental fate of their embryos to produce wingless or winged adult forms in response to high population density (i.e. crowded conditions). Although this maternal effect is well known, the mechanisms underlying transgenerational winged-morph determination remain largely unresolved. In the present study, the effects of different high-density treatment durations are tested on the vetch aphid Megoura crassicauda Mordvilko aiming to investigate how and when the density signals detected by mothers are transmitted to embryos. The duration of density treatment shows additive effects on both the number of crowded females producing winged aphids (winged-producers) and the number of winged progeny. In addition, even when high-density treatment is stopped, the production of winged offspring continues for several days and depends on the duration of treatment. The results indicate that mother aphids retain high-density signals for a period after removal of the stimulus. Furthermore, observations of the progeny sequence (i.e. the order in which the offspring are born) and the embryonic stages developing in the mothers reveal that high-density information may affect embryonic fate at the late embryonic stage immediately before cuticle formation.