Drosophila pseudoobscura

Drosophila pseudoobscura is a species of fruit fly, used extensively in lab studies of speciation. It is native to western North America.

Drosophila pseudoobscura
A D. pseudoobscura Male
Scientific classification
Kingdom:
Animalia
Phylum:
Arthropoda
Class:
Insecta
Order:
Diptera
Family:
Drosophilidae
Genus:
Drosophila
Subgenus:
Sophophora
Species group:
obscura group
Species subgroup:
pseudoobscura subgroup
Species:
D. pseudoobscura
Binomial name
Drosophila pseudoobscura
Frolova, 1929 [1]
Illustration of a D. pseudoobscura male

In 2005, D. pseudoobscura was the second Drosophila species to have its genome sequenced, after the model organism Drosophila melanogaster.[2]

Allopatric speciation has been induced by reproductive isolation in D. pseudoobscura after only eight generations using different food types, starch and maltose.[3]

Polyandry

Female Drosophila pseudoobscura are polyandrous, meaning they mate with more than one male. By mating with multiple males, polyandrous females have more genetically diverse offspring.[4]

Prevention of extinction

In the D. pseudoobscura population, some males have a harmful chromosome called sex ratio (SR), where an inactive Y-chromosome is transmitted.[5] If an SR male mates with a female, the female will produce only daughters. Monandry allows the spread of SR and increases the extinction risk in species having SR genes because the SR driver can spread quickly, enriching populations for females.[6] Polyandry decreases the SR gene frequency because the non-SR male sperm outcompete the SR male sperm.[7] Therefore, polyandry results in a decreased risk of extinction in the population.

Increased net offspring survival

Monandrous female D. pseudoobscura do not obtain sufficient sperm or a plenty of suitable sperm for the fertilization. Even though monandrous female experiencing multiple copulations can produce more eggs than polyandrous female experiencing multiple copulations, monandrous females produce less offspring that survive into adulthood than polyandrous females do.[8] This means that polyandrous females have higher egg-to-adult survival ratio than monandrous females, making the polyandrous females more fit.

Mate selection as a fitness benefit

Polyandrous relationships benefit females D. pseudoobscura. In males D. pseudoobscura, the variation in number of sperms shows the difference in benefits between polyandrous and monandrous females.[8] Males D. pseudoobscura ejaculate more sperm than any other Drosophila species, and it provides important nourishing factors to females and their offspring. The offspring viability benefits are increased by multiple and variable sperms through ejaculates.[8] There are no additional costs to polyandrous females, because there are not big differences in life expectancy between monandrous female experiencing multiple copulations and polyandrous female experiencing multiple copulations.[8]

Evolutionary consequences

Polyandry, in general, may have a few fitness consequences. Densely populated areas may have lower rates of polyandry due to environmental restraints such as geographic location and limited resources. This can greatly limit the survival and reproduction of offspring.[9] Therefore, in population dense areas, polyandrous behavior may actually be a fitness consequence since the environment significantly controls the number of offspring that survive.[9]

Polyandry could also pose genetic fitness consequences. Polyandry does not always result in the spread of the most adaptive genes. For example, some individuals may appear to be attractive due to genes that code for increased pheromone production.[10] As a result, attractive individuals are more likely to reproduce more often.[10] However, since these individuals do not always contain adaptive genes, multiple mating events do not always result in the propagation of adaptive genes.[10]

References
  1. "Drosophila pseudoobscura". Integrated Taxonomic Information System.
  2. S. Richards, Y. Liu, et al. (2005). "Comparative genome sequencing of Drosophila pseudoobscura: Chromosomal, gene, and cis-element evolution". Genome Research. 15 (1): 1–18. doi:10.1101/gr.3059305. PMC 540289. PMID 15632085.
  3. D. M. B. Dodd (1989). "Reproductive isolation as a consequence of adaptive divergence in Drosophila pseudoobscura" (PDF). Evolution. 43 (6): 1308–1311. doi:10.2307/2409365. JSTOR 2409365. PMID 28564510. Archived from the original (PDF) on 2008-12-17.
  4. Price, T.A.R.; Hodgson, D.J.; Lewis, Z.; Hurst, G.D.D.; Wedell, N. (2008). "Selfish Genetic Elements Promote Polyandry in a Fly". Science. 322 (5905): 1241–1243. Bibcode:2008Sci...322.1241P. doi:10.1126/science.1163766. PMID 19023079. S2CID 15806206.
  5. Price, Tom A. R.; Lewis, Zenobia; Smith, Damian T.; Hurst, Gregory D. D.; Wedell, Nina (2010). "Sex ratio drive promotes secual conflict and sexual coevolution in the fly drosophila pseudoobscura". Evolution. 64 (5): 1504–9. doi:10.1111/j.1558-5646.2009.00896.x. PMID 19922445. S2CID 205782563.
  6. Price, T.A.R.; Bretman, A.; Gradilla, A.C.; Reger, J; Taylor, M.L.; Giraldo-Perez, P.; Campbell, A.; Hurst, G.D.D.; Wedell, N. (2014). "Does polyandry control population sex ration via regulation of a selfish gene?". Proc. R. Soc. B. 281 (1783): 20133259. doi:10.1098/rspb.2013.3259. PMC 3996604. PMID 24695427.
  7. Price, T.A.R.; Hurst, G.D.D.; Wedell, N. (2010). "Polyandry Prevents Extinction". Current Biology. 20 (5): 471–475. doi:10.1016/j.cub.2010.01.050. PMID 20188561. S2CID 17941968.
  8. Gowaty, P.A.; Kim, Y.; Rawlings, J.; Anderson, W.W. (2010). "Polyandry increases offspring viability and mother productivity but does not decrease mother survival in Drosophila pseudoobscura". PNAS. 107 (31): 13771–13776. Bibcode:2010PNAS..10713771G. doi:10.1073/pnas.1006174107. PMC 2922267. PMID 20643932.
  9. Pai, Aditi; Feil, Stacy; Yan, Guiyun (2007-01-19). "Variation in polyandry and its fitness consequences among populations of the red flour beetle, Tribolium castaneum". Evolutionary Ecology. 21 (5): 687–702. doi:10.1007/s10682-006-9146-4. ISSN 0269-7653. S2CID 6829230.
  10. Boake, Christine R. B. (1985-03-01). "Genetic Consequences of Mate Choice: A Quantitative Genetic Method for Testing Sexual Selection Theory". Science. New Series. 227 (4690): 1061–1063. Bibcode:1985Sci...227.1061B. doi:10.1126/science.227.4690.1061. JSTOR 1694818. PMID 17794229. S2CID 30311676.
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