Detalhes do Documento

Environments are spatially and temporally dynamic, which poses a particular challenge to organisms as they try to tune their development to optimise their traits for a given environment. For some traits, it is beneficial to alter traits according to environmental conditions – a process known as developmental plasticity. Other traits need to maintain constant phenotypes across environmental conditions, known as developmental robustness. Even though we understand some of the mechanisms that give rise to plasticity or robustness in traits, little is known of how these processes are coordinated within organs so that these structures can exhibit both plastic and robust phenotypes. In Drosophila melanogaster, the wing development is well characterized and this organ displays both plasticity, in the form of wing size, and robustness, in the form of wing pattern. Previous studies in wing have shown that although the final pattern of the wing is robust, the rates of patterning in this organ show considerable variation throughout the third larval instar. Signalling via the steroid moulting hormone ecdysone is known to regulate both wing disc growth and patterning. This raises the question; how can the same signalling pathway coordinate both plastic and robust developmental responses? In this study, we genetically ablated the prothoracic gland (PGX), the gland that produces ecdysone, to explore how ecdysone concentrations affect the growth and patterning of the wing imaginal disc. By feeding PGX larvae a range of ecdysone concentrations, we determined how ecdysone, growth and patterning interact. We show that ecdysone triggers different responses in different traits. Early in the third instar, growth responds linearly to increasing ecdysone concentrations. Further, we observe significant differences between sexes in the response to ecdysone, with ecdysone affecting growth rates in fed males, but only affecting wing growth of the female wing discs when they are starved of protein. Wing disc patterning, on the other hand, shows threshold responses to ecdysone early in the third instar, and these responses to not differ between sexes. At the very end of development, ecdysone concentration does not affect disc growth rates. However, it does affect the rate of patterning for both Achaete and Senseless. These data suggest that ecdysone coordinates plastic with robust developmental processes via differences in how these processes respond to the hormone, both in nature and time.