Epitocia

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Atoke of Platynereis dumerilii with yellowish-brown body color
Female epitoke of Platynereis dumerilii , colored yellow by the eggs it contains
Male epitoke of Platynereis dumerilii , stained white in front by sperm, stained red in back by blood containing hemoglobin
Epitoke from Alitta succinea
Atoke from Alitta succinea

As Epitokie the characteristic is metamorphosis of certain marine annelid worms from different families of polychaete (Polychaeta) at the time of sexual maturity refers. During this process, the not yet able to mate, digging and crawling in the seabed - both females and males - are transformed into free-swimming epitoks that are ready to mate . If not just a part of the body but the entire body of the annelid is involved in the transformation, it is also called epigamy . In the Nereididae these epitoks are also referred to as Heteronereis , in the Syllidae as Heterosyllis .

Changes in epitoke versus atoke

While the polychaetes crawl on the seabed or dig in the sediment as atoken, i.e. as not yet sexually mature individuals, the transformation into the epitoken leads to noticeable changes in the shape that facilitate free swimming. The coelom of the numerous segments that contain the gonads is filled with egg cells in the female and with sperm in the male . Simultaneously with the maturation of the germ cells, the intestinal canal and the muscles are broken down. The parapodia and the cirrus sitting on them are widened like a leaf to form swimming oars. At the same time, the head and eyes are enlarged.

The swarming male and female Epitoken come together in large numbers to mate. After the gametes are released into the open sea, which in many cases occurs when the skin of the epitokes burst open, both sexual partners die. The eggs are fertilized in the open sea water and develop into free-swimming trochophora larvae.

The swarming out of the epitoken typically occurs at a certain moon phase . The maturation of gametes is inhibited by a hormone that is produced in the back of the brain and spread through the blood vessel system. When the production of this hormone ends, the metamorphosis to the epitoke begins.

While in the Palolowürmern ( Palola ) in the family Eunicidae with the studied best way Palola viridis the foremost section remains of the animal unchanged and the gonadentragende rear main part pinches the swarming as Epitoke forms in epitoken kinds of families Nereididae - including Alitta succinea and Platynereis dumerilii - as well as Syllidae - including Eusyllis blomstrandi , Odontosyllis ctenostoma , Exogone gemmifera and Autolytus longeferiens - the entire body of the males and females the epitoke swarm stage. In the nereid Alitta virens , only the slightly modified male swarms, while the externally hardly changed female remains on the ground, but both sexual partners die after mating. In Platynereis megalops , the male wraps around the female and bursts open, so that the sperm enter the female and internal fertilization takes place.

Schizogamy

Autolytus sp. cuts off head-bearing epitoken.

A distinction is to be made between epigamy and schizogamy , in which males and females cut off a larger number of buoyant epitoks through sprouting or budding . There is also talk of a generation change in which the benthic atoke, the foster animal, produces swarming epitoks ( stolons ) ready for mating through asexual reproduction , which die after sexual reproduction has taken place, while the atoke continues to live and can produce new epitoks. This type of reproduction is widespread in the family Syllidae , especially in the genus Autolytus with, among other things, the two species Autolytus prolifer and Autolytus purpureomaculatus .

literature

  • Charles Houillon: Sexuality. Textbook for biologists and medical professionals. Translated from the French by Prof. Rudolf Altevogt, Münster. Friedrich Vieweg and Son, Braunschweig 2013. S. 86f.
  • George Karleskint, Richard Turner, James Smal: Introduction to Marine Biology. 3rd edition, Brooks / Cole, Cengage Learning, Belmont (California) 2009. p. 237.
  • E. Hébert Chatelain, S. Breton, H. Lemieux, PU Blier: Epitoky in Nereis (Neanthes) virens (Polychaeta: Nereididae): a story about sex and death. In: Comparative biochemistry and physiology. Part B, Biochemistry & molecular biology. Volume 149, Number 1, January 2008, pp. 202-208, doi : 10.1016 / j.cbpb.2007.09.006 , PMID 17942355 .
  • PJ Hayward, JS Ryland: Handbook of the Marine Fauna of North-West Europe. Oxford University Press, Oxford 1995. Nereidae , pp. 206-212, here p. 208.

Web links

Commons : Epitoken  - collection of images, videos and audio files

Individual evidence

  1. ↑ a b c Antje HL Fischer, Thorsten Henrich, Detlev Arendt: The normal development of Platynereis dumerilii (Nereididae, Annelida) . In: Frontiers in Zoology . 7, No. 1, 2010, p. 31. doi : 10.1186 / 1742-9994-7-31 . PMID 21192805 . PMC 3027123 (free full text).