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How organisms evolve under extreme environmental changes is a critical question in the face of global climate change. Genetic accommodation is an evolutionary process by which natural selection acts on novel phenotypes generated through repeated encounters with extreme environments. In this study, polyphenic and monophenic strains of theblackmutant tobacco hornworm,Manduca sexta, were evolved via genetic accommodation of heat stress-induced phenotypes, and the molecular differences between the two strains were explored. Transcriptomic analyses showed that epigenetic and hormonal differences underlie the differences between the two strains and their distinct responses to temperature. DNA methylation had diverged between the two strains potentially mediating genetic assimilation. Juvenile hormone (JH) signaling in the polyphenic strain was temperature sensitive, whereas in the monophenic strain, JH signaling remained low at all temperatures. Although 20-hydroxyecdysone titers were elevated under heat shock conditions in both strains, the strains did not differ in the titers. Tyrosine hydroxylase was also found to differ between the two strains at different temperatures, and its expression could be modulated by topical application of a JH analog. Finally, heat shock of unselectedblackmutants demonstrated that the expression of the JH-response gene,Krüppel-homolog 1(Kr-h1), increased within the first 30 min of heat shock, suggesting that JH levels respond readily to thermal stress. Our study highlights the critical role that hormones and epigenetics play during genetic accommodation and potentially in the evolution of populations in the face of climate change. 

Aposematic coloration offers an opportunity to explore the molecular mechanisms underlying canalization. In this study, the role of epigenetic regulation underlying robustness was explored in the aposematic coloration of the milkweed bug,Oncopeltus fasciatus. Polycomb(Pc) andEnhancer of zeste(E(z)), which encode components of the Polycomb repressive complex 1 (PRC1) and PRC2, respectively, andjing, which encodes a component of the PRC2.2 subcomplex, were knocked down in the fourth instar ofO. fasciatus. Knockdown of these genes led to alterations in scutellar morphology and melanization. In particular, whenPcwas knocked down, the adults developed a highly melanized abdomen, head and forewings at all temperatures examined. In contrast, theE(z)andjingknockdown led to increased plasticity of the dorsal forewing melanization across different temperatures. Moreover,jingknockdown adults exhibited increased plasticity in the dorsal melanization of the head and the thorax. These observations demonstrate that histone modifiers may play a key role during the process of canalization to confer robustness in the aposematic coloration.