Figure 3. Creation of species boundaries by regulatory evolution.

(A) Hybrids between melanogaster and synthetica arrest in pupae and do not develop further, even at 17C. The sex of the parents did not affect the outcome. Pupae shown in the pictures are more than one month old. (B) Scheme of a classical Dobzhansky-Muller mechanism for speciation, where all mutations occur in one of the populations (“derived”), and the hybrids between the “ancestral” (aabb) and “derived” (AABB) populations are lethal. (C) High definition and depth of field images of Drosophila synthetica after several generations of coexistence with D. melanogaster. Image obtained with a Keyence VHX-600 microscope. Eyes are pale in addition to small. A D.melanogaster eye is shown for comparison in the upper right corner. (D) General model for the creation of species boundaries based on the modification of transcription factors and the subsequent appearance of cryptic enhancers. This could be a mechanism to create synthetic species and prevent hybridization of transgenic animals with natural populations. The case of Drosophila synthetica is shown. Years correspond to the first appearance of the mutation or transgene in a Drosophila laboratory.