The Drosophila quinaria species group is a speciose lineage of mushroom-feeding flies studied for their specialist ecology, their parasites, population genetics, and the evolution of immune systems.

For instance, as a consequence of their mushroom-feeding ecology, Quinaria species are frequently infected by nematodes of the genus Howardula.

[5] The ancestor of Quinaria species and related flies likely switched from a generalist ecology to become exclusively mushroom-feeders.

From there, different mushroom-feeding lineages emerged, some of which reverted to feeding on decaying vegetation,[8] such as Drosophila quinaria.

This observation ties behavioural change to infection status, specifically identifying compounds that the fly becomes more or less averse to.

[8] Evolutionary studies in these various mushroom-feeding Drosophila have contributed to understanding how symbiotic bacteria can drastically affect host evolution,[12] the impact of various genetic elements in natural populations,[13][14] and speciation.

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.

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.

In the Wnt pathway, the Wingless gene encodes a ligand involved in the local development of melanin synthesis in the wing.

Studies in the major genetic model organism Drosophila melanogaster are how the Wnt signalling pathway was first suspected.

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.

[19] Speciation describes when two populations diverge sufficiently such that they are considered different species, often because they can no longer successfully reproduce with one another.

[22] The D. subquinaria species complex is made all the more challenging to interpret by continued gene flow between D. recens and D.

[24] Ginsberg and colleagues[25] showed that the direction of gene flow is biased from D. recens into sympatric populations of D. subquinaria.

These endosymbionts can have a number of different consequences from cytoplasmic incompatibility, male-killing, feminization, or defensive symbiosis.

In different insects and arthropods, Wolbachia manipulate host reproduction to increase the number of females in the population.

Male-killing results in the offspring of flies being entirely female, the biological sex with the higher reproductive output.

Female flies lay hundreds of eggs over their lifespan, and can store sperm in a specialized organ called the spermatheca.

[43] The mechanism behind how mushroom-feeding flies can selectively maintain their gut microbiota despite feeding on rotting mushroom is still unclear.

These pose important challenges for the host immune system with significant impacts on fitness and fertility.

For instance, D. falleni and D. neotestacea are sterilized by Howardula aoronymphium nematodes, while related species resist infection.

[6] This sterilization is associated with reduced expression of genes involved in egg development, and increases in cuticle synthesis pathways.

In D. melanogaster, specialized blood cells called lamellocytes that regulate local melanin synthesis during capsule formation.

In some species, the bacterial symbiont Spiroplasma protects related mushroom-feeding Drosophila from wasp parasitization using toxins that selectively kill the wasp larva but not the host fly, an interaction well-characterized using comparisons between Spiroplasma from D. melanogaster and the mushroom-feeding Drosophila neotestacea.

Notably, natural selection on the immunity and antiviral pathways in D. innubila differ markedly from D. melanogaster, implying divergent evolutionary pressures.

These evolutionary patterns in mushroom-breeding Drosophila and other fruit flies suggests that the immune system's effectors (like antimicrobial peptides) are directly shaped by host ecology.