Various Quinaria group species have contributed to genetic studies in different fashions. So far the genomes of four Quinaria species,
D. guttifera, D. innubila,
D. quinaria, and
D. palustris have been sequenced. Additional sequence data has been generated for
Drosophila falleni and
Drosophila phalerata. The genome of
D. innubila was sequenced for a study in 2019, and boasts a very complete assembly rivalling that of the classic genetic model
Drosophila melanogaster. In September 2020, a study of
Drosophila sex pheromone communication sequenced the genomes of
D. quinaria, and
D. palustris, as well as many outgroup lineages of the Quinaria species group.
Gene regulation on the fly The patterning of
Drosophila wings has long been of interest to evolutionary biologists as understanding the genetic changes underlying wing patterning helps understand how
evolution can act to promote novel designs.
Drosophila guttifera (the "Polka-dotted fruit fly") has conspicuous dot patterns on its wings made of black
melanin. Different variations of these dot patterns occur in different Quinaria group species, ranging from only one melanin spot on the wing band at the anterior costal vein in
D. innubila, to two wing band spots in
D. phalerata, to conspicuous polka-dots in
D. guttifera. One method to study these patterns has been to compare gene regulation amongst different
Drosophila species. The
Drosophila Wnt signalling pathway regulates wing development. In the Wnt pathway, the
Wingless gene encodes a
ligand involved in the local development of
melanin synthesis in the wing. Other genes in the Wnt signalling pathway such as
yellow and
ebony are also involved in melanin regulation. Studies in the major genetic model organism
Drosophila melanogaster are how the Wnt signalling pathway was first suspected. These studies implicated genes such as
Wingless in wing development through mutations in Wnt signalling and the
Wingless gene. Following this, studies in different species such as
Drosophila biarmipes and
Drosophila guttifera revealed different patterns of
yellow gene expression. As a result of these comparative studies, and owing to its attractive wing patterning,
D. guttifera is now used as a comparative model to understand gene network interactions amongst
Wingless,
yellow, and other Wnt signalling genes. Understanding how these networks cooperate to regulate wing patterning also helps scientists understand how gene regulatory networks work in other systems such as health or development. Using conspicuous patterns like polka dot distribution on wings makes understanding general principles of gene regulation more approachable. In 2015, the genome of
Drosophila guttifera was sequenced by the laboratory of
Sean B. Carroll providing an answer on how different wing patterns emerge in this species. The authors found that additional copies of genetic switches called "
enhancers" drives the polka-dot pattern on the wings of
D. guttifera. These enhancers were a subset of
cis-regulatory elements. As such, new evolutionary patterns can arise without modifying the active gene, by instead modifying existing enhancer regions. This leads to different patterns of gene expression, in the case of
D. guttifera, resulting in different patterning on its wings. however the offspring are very sickly. Thus, these two species are almost fully reproductively isolated, despite overlapping in geographic range. One reason for this is behavioural, driven by
pheromones.
D. subquinaria females readily avoid mating with males from other species, but surprisingly
D. subquinaria females also avoid mating with males from the same species in
allopatric populations. However
D. recens females do not distinguish between males from different populations.
Pheromones in the
cuticle of the males differ between geographic ranges of
D. subquinaria, possibly explaining how females distinguish males from different populations. This has led to
D. subquinaria females in sympatry with
Wolbachia-infected
D. recens to be more choosy when making a
mate choice, while
D. subquinaria females that are not sympatric with
D. recens do not make this distinction. Beyond these two species,
Drosophila transversa is also capable of hybridization with both
D. subquinaria and
D. recens. Ginsberg and colleagues showed that the direction of gene flow is biased from
D. recens into sympatric populations of
D. subquinaria. This is likely due to increased one-directional mating success between
D. recens females and
D. subquinaria males in sympatry, but may also depend on the efficiency with which the
D. recens X chromosome acts in a
D. subquinaria genetic background. There is also a
sex ratio-distorting X chromosome in
D. recens that may factor in to both speciation between
D. recens and
D. subquinaria, and selection on
D. recens populations more generally. This
selfish X chromosome is one of a number of
selfish genetic elements in the Quinaria and
Testacea Drosophila species groups. In
D. recens, females with two copies of the selfish X are sterile, while males have reduced fertility. These deleterious effects are offset by the transmission advantage that the X chromosome has in males, where it kills off all Y-bearing sperm, leaving that male to sire only selfish X-bearing daughters, which in turn produce more sons that will again sire only daughters. ==Microbial symbiosis==