Amazon molly

The Amazon molly (Poecilia formosa) is a freshwater fish native to warm, fresh waters between Tuxpan River in northeastern Mexico and the Rio Grande and the Nueces River in the southern parts of the U.S. state of Texas.[1][3] It reproduces through gynogenesis, and essentially all individuals are females. The common name acknowledges this trait as a reference to the Amazon warriors, a female-run society in Greek mythology.[4]

Amazon molly
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Cyprinodontiformes
Family: Poeciliidae
Genus: Poecilia
Species:
P. formosa
Binomial name
Poecilia formosa
(Girard, 1859)
Synonyms[2]
  • Limia formosa Girard, 1859
  • Mollienesia formosa (Girard, 1859)

Reproduction

Reproduction is through gynogenesis, which is sperm-dependent parthenogenesis. This means that females must mate with a male of a closely related species, but the sperm only triggers reproduction and is not incorporated into the already diploid egg cells the mother is carrying (except in extraordinary circumstances). This results in clones of the mother being produced en masse.[5] This characteristic has led to the Amazon molly becoming an all-female species.[6] Other all-female species include the New Mexico whiptail, desert grassland whiptail lizard, and blue-spotted salamander.

There are four stages in the reproduction of the Amazon molly. In the first step, there is a diploid cell that is activated by a sperm cell but does not incorporate the genetic makeup of the sperm. The second step shows the copying of the two single chromosomes to make two doubled chromosomes. In the third step, the two chromosomes are being pulled apart to opposite sides of the cell. In the fourth and final step, there are two daughter cells, each with two single chromosomes, an exact replica of the mother cell.
The Amazon molly reproduces through gynogenesis. This image shows that the genetic material of the male is not incorporated into the offspring of the female. And the daughter cells produced are copies of the mother cell.[7]

In nature, the Amazon molly typically mates with a male from one of four different species, either P. latipinna, P. mexicana, P. latipunctata, or occasionally P. sphenops.[8] One other male that could possibly exist in the Amazon molly's natural range that could induce parthenogenesis in Amazon molly females is the triploid Amazon molly male. These triploid males are very rare in nature and are not necessary in the reproduction of the species, which is why the species is considered to be all female.

Since the male's sperm is not contributing to the genetic makeup of the offspring, it may seem non-beneficial for males of closely related species to participate in mating with the Amazon molly, though research shows that females of other species, such as the Atlantic molly, are trend conscious and are more likely to mate with a male of their species if they see that male mate with an Amazon molly.[9] Therefore, the Amazon molly can only live in habitats that are also occupied by a species of male that will reproduce with them.[6]

The Amazon molly reaches sexual maturity one to six months after birth, and typically has a brood between 60 and 100 fry (young) being delivered every 30–40 days. This lends itself to a large potential for population growth as long as host males are present. The wide variability in maturity dates and brood sizes is a result of genetic heritage, varying temperatures, and food availability. They become sexually mature faster and produce larger broods in warm (approximately 27 °C or 80 °F) water that provides an overabundance of food.[10]

The Amazon molly has been reproducing asexually for about 100,000-200,000 years.[11] This is about 500,000 generations of Amazon molly. Asexual lineages typically go extinct after 10,000-100,000 generations.[5] There is research being done to determine how the Amazon molly has not gone extinct or developed a Muller's ratchet of mutations. Researchers believe the answer is in the genome of the Amazon molly,[12] yet more research must be done to determine this.

P. formosa is a hybrid species and P. mexicana is one of the parental species.[13] Its other progenitor is most likely an extant, as yet undescribed, subspecies of P. latipinna or an extinct ancestor of P. latipinna.

References
  1. NatureServe.; Daniels, A. (2019). "Poecilia formosa". IUCN Red List of Threatened Species. 2019: e.T191747A130033075. doi:10.2305/IUCN.UK.2019-2.RLTS.T191747A130033075.en. Retrieved 19 November 2021.
  2. Eschmeyer, William N.; Fricke, Ron & van der Laan, Richard (eds.). "Poecilia formosa". Catalog of Fishes. California Academy of Sciences. Retrieved 3 April 2019.
  3. Froese, Rainer; Pauly, Daniel (eds.) (2019). "Poecilia formosa" in FishBase. February 2019 version.
  4. Schlupp, Ingo; Riesch, Rüdiger & Tobler, Michael (July 2007). "Amazon mollies". Current Biology. 17 (14): R536–R537. doi:10.1016/j.cub.2007.05.012. PMID 17637348. S2CID 27224117.
  5. Heubel, Katja (2004). Population ecology and sexual preferences in the mating complex of the unisexual Amazon molly Poecilia formosa (GIRARD, 1859) (PhD). Universität Hamburg. S2CID 82258075.
  6. Schlupp, Ingo; Riesch, Rüdiger; Tobler, Michael (July 2007). "Amazon mollies". Current Biology. 17 (14): R536–R537. doi:10.1016/j.cub.2007.05.012. PMID 17637348.
  7. Janko, Karel; Eisner, Jan; Mikulíček, Peter (2019-01-24). "Sperm-dependent asexual hybrids determine competition among sexual species". Scientific Reports. 9 (1): 722. Bibcode:2019NatSR...9..722J. doi:10.1038/s41598-018-35167-z. ISSN 2045-2322. PMC 6345890. PMID 30679449.
  8. Froese, Rainer and Pauly, Daniel, eds. (2019). "Poecilia formosa" in FishBase. February 2019 version.
  9. Balcombe, Jonathan (2017). What a fish knows: the inner lives of our underwater cousins. Scientific American/Farrar, Straus, and Giroux. p. 190.
  10. Fredjikrang. "The Importance of the Reproductive Techniques of Poecilia formosa". petfish.net. Archived from the original on 16 December 2006.
  11. amazon-molly-genome-research (2019-01-09). "The Amazon Molly's Ability to Clone Itself". www.txstate.edu. Retrieved 2019-10-31.
  12. "Survival of all-female fish species points to its DNA | Biodesign Institute | ASU". biodesign.asu.edu. Archived from the original on 2021-10-07. Retrieved 2019-10-31.
  13. Schartl, Manfred; Wilde, Brigitta; Schlupp, Ingo; Parzefall, Jakob (October 1995). "Evolutionary Origin of a Parthenoform, the Amazon Mollypoecilia Formosa, on the Basis of a Molecular Genealogy". Evolution; International Journal of Organic Evolution. 49 (5): 827–835. doi:10.1111/j.1558-5646.1995.tb02319.x. PMID 28564866. S2CID 205779353.
  • No sex for all-girl fish species BBC News, 23 April 2008
  • Heubel, Katja U.: Population ecology and sexual preferences in the mating complex of the unisexual Amazon molly Poecilia formosa (Girard, 1859).Hamburg, University, Diss., 2004.
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