Partial reduction of Hsp90 increases expression of morphological novelty in qualitative traits of Drosophila and Arabidopsis, but the extent to which the Hsp90 chaperone also controls smaller and more likely adaptive changes in natural quantitative traits has been unclear.
Consequently, consideration of mechanisms of phylogenetic change that have been found in reality to be non-gradual is increasingly common in the field of evolutionary developmental biology, particularly in studies of the origin of morphological novelty.
This implies that transposons have made a significant contribution to the onset of morphological novelty.
Basically, some have argued that noncoding cis-regulatory mutations are a primary source of morphological novelty because regulatory change is thought to be more likely to have spatially or temporally restricted effects than protein sequence change (Stern 2000, Carroll 2005).
Hanken [ 1] noted that miniaturization is often not only associated with the reduction of characters, but also with the evolution of morphological novelties and some of the developmentally truncated miniature cyprinids offer fascinating examples for this claim.
Thus, it has been hypothesized that developmental transcription factors are more likely to evolve new functions and so coordinate the development of viable morphological novelty [ 4].
Therefore, in addition to cis-regulatory changes that led to a heterochronic CYC2 gene expression shift in the Brassicaceae, promoting corolla monosymmetry evolution [ 10, 12], also a divergence of trans-acting CYC2 proteins likely contributed to the establishment of this morphological novelty.
The development of intestinal complexity in terapontids exhibits several elements of heterochronic processes [ 74, 75], where ontogeny is modified to produce morphological novelty.
Limb loss in snakes and whales also demonstrates the importance of paedomorphosis in the evolution of morphological novelties.
