Macrostomum hystrix

Macrostomum hystrix
Temporal range: No fossils known
Macrostomum hystrix adult
Scientific classification
Kingdom: Animalia
Phylum: Platyhelminthes
Class: Turbellaria
Order: Macrostomida
Family: Macrostomidae
Genus: Macrostomum
Species: M. hystrix
Binomial name
Macrostomum hystrix
Luther, 1905[1]

Macrostomum hystrix is a free-living flatworm of the genus Macrostomum. It is small, transparent and a simultaneous hermaphrodite.

Biology

Macrostomum hystrix is capable of hypodermic insemination. In this process sperm is injected through the epidermis into the parenchyma of the mating partner. This is done by a needle-like stylet, which is the male copulatory organ. The stylet has a rigid and pointed distal thickening as well as a subterminal stylet opening which can puncture the epidermis of the mating partner. The sperm are highly motile, small and simple but have no flagellates. The female antrum shows a simple anatomy and is only involved in laying eggs.[2]

Sperm of Macrostomum hystrix
The needle-like stylet of Macrostomum hystrix. Further the seminal vesicle as well as developing eggs can be recognized.
The needle-like stylet of Macrostomum hystrix. Further the seminal vesicle as well as developing eggs can be recognized.

In isolated worms it has been shown that Macrostomum hystrix does not only use hypodermic insemination for outbreeding but also self-fertilization, also known as selfing. By this they inject their own sperm mainly into their head due to physical constraints. From there the sperm apparently migrate to the site of fertilization. Worms that were isolated showed significantly more sperm in their head compared to worms that had the opportunity to cross fertilize.[3] Macrostomum hystrix prefers outbreeding if partners are available because selfing also has costs. The amount of offspring of worms that selfed is reduced as well as the offspring's survival. As a consequence Macrostomum hystrix shows delayed selfing. It only starts selfing in the extended absence of mating partners and after a considerable delay, so delayed selfing represents a conditional reproductive strategy which allows them to deal with periodic conditions of low mate abundance.[4]

References

  1. ↑ Luther, A. (1905). "Zur Kenntnis der Gattung Macrostoma" (PDF). Festschrift für Palmén, Helsingfors.
  2. ↑ Schärer, Lukas; Littlewood, D. Timothy J.; Waeschenbach, Andrea; Yoshida, Wataru; Vizoso, Dita B. (2011-01-25). "Mating behavior and the evolution of sperm design". Proceedings of the National Academy of Sciences 108 (4): 1490–1495. doi:10.1073/pnas.1013892108. ISSN 0027-8424. PMC 3029721. PMID 21220334.
  3. ↑ Ramm, Steven A.; Schlatter, Aline; Poirier, Maude; Schärer, Lukas (2015-07-22). "Hypodermic self-insemination as a reproductive assurance strategy". Proceedings. Biological Sciences / The Royal Society 282 (1811). doi:10.1098/rspb.2015.0660. ISSN 1471-2954. PMC 4528547. PMID 26136446.
  4. ↑ Ramm, S. A.; Vizoso, D. B.; Schärer, L. (2012-12-01). "Occurrence, costs and heritability of delayed selfing in a free-living flatworm". Journal of Evolutionary Biology 25 (12): 2559–2568. doi:10.1111/jeb.12012. ISSN 1420-9101.

External links

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