Comparative Transcriptomics in Two Extreme Neopterans Reveals General Trends in the Evolution of Modern Insects.

The success of neopteran insects, with 1 million species described, is associated with developmental innovations such as holometaboly and the evolution from short to long germband embryogenesis. To unveil the mechanisms underlining these innovations, we compared gene expression during the ontogeny of two extreme neopterans, the cockroach Blattella germanica (polyneopteran, hemimetabolan, and short germband species) and the fly Drosophila melanogaster (endopterygote, holometabolan, and long germband species). Results revealed that genes associated with metamorphosis are predominantly expressed in late nymphal stages in B. germanica and in the early-mid embryo in D. melanogaster. In B. germanica the maternal to zygotic transition (MZT) concentrates early in embryogenesis, when juvenile hormone factors are significantly expressed. In D. melanogaster, the MZT extends throughout embryogenesis, during which time juvenile hormone factors appear to be unimportant. These differences possibly reflect broad trends in the evolution of development within neopterans, related to the germband type and the metamorphosis mode.