Figure 1.
Design of a genetic circuit with selected components that form a synthetic species barrier.
(A) The 5 genetic elements used: transcription factor glass, enhancer GMR, transcription factor gal4, enhancer UAS and a constitutively activated form of ras. (B,C) Arrangement of the genetic elements in two modules, a killing module (B) composed by two independent transgenes, GMR-gal4 and UAS-rasv12,and a switch that depending on the presence or absence of the transcription factor glass can switch the killing module ON and OFF (C). (D) In the absence of Glass, activation of the killing module is not possible and the flies survive. However, in the presence of Glass, expression of the constitutively active form of ras kills the animal.
Table 1.
Crosses between Drosophila synthetica and Drosophila melanogaster.
Figure 2.
Morphological traits of Drosophila synthetica.
(A–B) Scanning electronic microscopy (SEM) images of Drosophila synthetica flies. Eye is small due to lack of glass. (C–D) Wings of Drosophila synthetica show extraveins in the lateral regions of the wing (D) compared to the Drosophila melanogaster wing (C).
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.