|Drosophila simulans adult female|
Drosophila simulans complex
This species was discovered by the fly geneticist Alfred Sturtevant in 1919, when he noticed that the flies used in Thomas Hunt Morgan's laboratory at the Columbia University were actually two distinct species: D. melanogaster and D. simulans. Males differ in the external genitalia, while trained observers can separate females using colour characteristics. D. melanogaster females crossed to D. simulans males produce sterile F1 females and no F1 males. The reciprocal cross produces sterile F1 males and no female progeny.
Drosophila simulans was found later to be closely related to two island endemics, D. sechellia and D. mauritiana. D. simulans will mate with these sister species to form fertile females and sterile males, a fact that has made D. simulans an important model organism for research into speciation. D. simulans are monomorphic in their pheromone profiles where both males and females largely produce the cuticular hydrocarbon pheromone 7-tricosene (7-T). The ability of males within the D. melanogaster subgroup to discriminate between conspecific and heterospecific females is due in part to the differential valence of the cuticular hydrocarbon 7,11-heptacosadiene (7,11-HD), which is produced by D. melanogaster and D. sechellia females. Perfuming a D. simulans female with 7,11-HD is sufficient to suppress D. simulans male courtship.
Wolbachia infections give insight into how certain species of Drosophila are related. Through the analysis of cytoplasmic incompatibility and similar mitochondrial DNA, it has been shown that D. simulans and D. mauritiana are more closely related to each other than to D. sechellia. Cytoplasmic incompatibility causes egg and sperm cells to fail in creating viable offspring, a common feature in Wolbachia-infected D. simulans and D. mauritiana individuals. Drosophila sechellia has significantly distinct mitochondrial DNA, further emphasizing the evolutionary differences between the three species.
Relationship with Wolbachia
Infections of Wolbachia, a commonly infectious strain of bacteria observed in many insects such as Trichogramma and Muscidifurax uniraptor wasps, are transmitted between generations of Drosophila simulans. Wolbachia is inherited through maternal heredity. The infection is maintained through a process involving cytoplasmic incompatibility (CI) in which Wolbachia hinders uninfected individuals from producing offspring.
Wolbachia has formed a symbiotic relationship with D. simulans. Wolbachia infects the cytoplasm of a cell; once infected, a female fly will pass the infection to all resulting offspring through the cytoplasm of her eggs.
Two separate Wolbachia infection events have occurred in the ancestors of D. simulans, suggesting the evolutionary advantage of Wolbachia infections to D. simulans.
Effects of Wolbachia infection
Wolbachia infections have significantly decreased virus-induced mortality in D. simulans. While the mechanism for the decreased virus-induced mortality is still unknown, Wolbachia provides antiviral properties, potentially perpetuated by outcompeting the virus. Furthermore, different strains of Wolbachia have varying levels of antiviral properties; for example, some strains can protect against DCV (Drosophila C virus) while other strains cannot.
Benefits of Wolbachia studies
Drosophila simulans has also played an important role in sequencing the genomes for certain Wolbachia strains. D. simulans eggs were infected with the wRi Wolbachia strain in order to better understand how Wolbachia recombines. Further studies can help understand how Wolbachia strains coexist with D. simulans individuals. Studying Wolbachia strains and their mechanisms of infection can provide insight into the complex phylogenetic relationships of arthropods.
- Jallon, Jean-Marc; David, Jean R. (1987). "Variations in Cuticular Hydrocarbons Among the Eight Species of the Drosophila Melanogaster Subgroup". Evolution. 41 (2): 294–302. doi:10.1111/j.1558-5646.1987.tb05798.x. ISSN 1558-5646. PMID 28568760.
- Billeter, Jean-Christophe; Atallah, Jade; Krupp, Joshua J.; Millar, Jocelyn G.; Levine, Joel D. (2009-10-15). "Specialized cells tag sexual and species identity in Drosophila melanogaster". Nature. 461 (7266): 987–991. doi:10.1038/nature08495. ISSN 1476-4687. PMID 19829381.
- Coyne, J. A.; Crittenden, A. P.; Mah, K. (1994-09-02). "Genetics of a pheromonal difference contributing to reproductive isolation in Drosophila". Science. 265 (5177): 1461–1464. ISSN 0036-8075. PMID 8073292.
- Seeholzer, Laura F.; Seppo, Max; Stern, David L.; Ruta, Vanessa (2018). "Evolution of a central neural circuit underlies Drosophila mate preferences". Nature. 559 (7715): 564–569. doi:10.1038/s41586-018-0322-9. ISSN 1476-4687. PMID 29995860.
- Wolff, J N; Nafisinia, M; Sutovsky, P; Ballard, J W O (2012). "Paternal transmission of mitochondrial DNA as an integral part of mitochondrial inheritance in metapopulations of Drosophila simulans". Heredity. 110 (1): 57–62. doi:10.1038/hdy.2012.60. PMC 3522233. PMID 23010820.
- Rousset, F.; Solignac, M. (1995). "Evolution of single and double Wolbachia symbioses during speciation in the Drosophila simulans complex". Proc. Natl. Acad. Sci. USA. 92 (14): 6389–6393. doi:10.1073/pnas.92.14.6389. PMC 41523. PMID 7604001.
- Dobson, SL; Rattanadechakul, W; Marsland, EJ (5 May 2004). "Fitness advantage and cytoplasmic incompatibility in Wolbachia single- and superinfected Aedes albopictus". Heredity. 93 (2): 135–142. doi:10.1038/sj.hdy.6800458. PMID 15127087.
- Rousset, F.; Solignac, M. (July 1995). "Evolution of single and double Wolbachia symbioses during speciation in the Drosophila simulans complex" (PDF). Proc. Natl. Acad. Sci. 92: 6389–6393. doi:10.1073/pnas.92.14.6389. PMC 41523.
- Osborne, S., Leong, Y., O’Neill, S., Johnson, K. 2009. Variation in Antiviral Protection Mediated By Different Wolbachia Strains in Drosophila simulans. PLOS. 11: e1000656-e1000656.
- Klasson, L.; Westberg, J.; Sapountiz, P.; Näslund, K.; Lutnaes, Y.; Darby, A.; Veneti, Z.; Chen, L.; Braig, H.; Garrett, R.; Bourtzis, K.; Andersson, S. (2009). "The mosaic genome structure of the Wolbachia wRi strain infecting Drosophila simulans". PNAS. 106: 5725–5730. doi:10.1073/pnas.0810753106. PMC 2659715. PMID 19307581.
- Sturtevant, A.H. (1919). "A new species closely resembling Drosophila melanogaster". Psyche. 26: 153–155. doi:10.1155/1919/97402.
- Sturtevant, A.H. The North American Species of Drosophila. Carnegie Institute of Washington, 1921.