Fig. 4. Diagrams depicting developmental gene networks and proposed gene relationships, as suggested by the current research. (A) Organization of a gene network involving JH-responsive genes from the signal transduction, transcription and translation factors, and the cuticle and muscle ontogeny categories. Solid arrows represent a simple hierarchical cascade, whereas dotted arrows represent the more complex feedback between levels that probably occurs. (B) Apparent relationship between hexamerin titer and JH availability (Zhou et al., 2006a; Zhou et al., 2006b), as well as other putative intrinsic and extrinsic caste-regulatory factors. Solid arrows represent what is known from prior and current research, whereas dotted arrows illustrate the proposed relationships. In this scheme, the hexamerins can be considered an environmentally-responsive switching mechanism (Wheeler, 1986) that modulates JH-dependent morphogenesis.