Epitoky

{{Short description|Sexual maturation process in marine worms}} [[File:Syllid polychaete undergoing epitoky.jpg|thumb|right|200px|Syllid polychaete budding epitokes for the purpose of sexual reproduction.]] [[File:Alitta succinea (epitoke).jpg|thumb|right|200px|''Alitta succinea'', the common clam worm (Nereididae) in epitoky stage]]

'''Epitoky''' is a process that occurs in many species of polychaete marine worms wherein a sexually immature worm (the '''atoke''') is modified or transformed into a sexually mature worm (the '''epitoke'''). In many species, the reproductive unit eventually detaches from the parent body as a distinct and independent individual called a stolon.<ref>[https://pmc.ncbi.nlm.nih.gov/articles/PMC5050598/ On the role of the proventricle region in reproduction and regeneration in Typosyllis antoni (Annelida: Syllidae)]</ref> Stolons are pelagic morphs capable of sexual reproduction.<ref>{{cite book|last=Pechenik|first=Jan I.|title=Biology of the Invertebrates, Seventh Edition|year=2015|publisher=McGraw-Hill Education|location=New York, NY|isbn=978-0-07-352418-4|pages=302–304}}</ref> Unlike the immature form, which is typically benthic (lives on the bottom), epitokes are specialized for swimming as well as reproducing. The primary benefit to epitoky is increased chances of finding other members of the same species for reproduction.

There are two methods in which epitoky can occur: '''schizogamy''' and '''epigamy'''.

==Schizogamy== Many species go through '''schizogamy'''. There are two types of schizogamy: '''scissiparity''' and '''gemmiparity'''. In worms that use scissiparity, the posterior segments undergo modification before separating from the parent body as a single stolon. In species that reproduce by gemmiparity, several stolons may be produced at the same time, either as a long chain consisting of a series of connected stolons that separate when fully mature, or as separate stolons developing from the posterior end of the body.<ref>[https://www.google.no/books/edition/Pleistoannelida_Errantia_II/PoVaEAAAQBAJ?hl=en&gbpv=1&dq=Schizogamy+scissiparity+stolon+gemmiparity&pg=PA169&printsec=frontcover Handbook of Zoology, Volume 4, Annelida - Pleistoannelida, Errantia II - Page 169]</ref> Atokes may then survive to produce additional stolons in subsequent reproductive cycles.

==Epigamy== '''Epigamy''' is another common way to form epitokes. For species that use this method, the atoke undergoes physiological and morphological modifications as it transforms into the epitoke.<ref name="Chatelain">{{cite journal|doi=10.1016/j.cbpb.2007.09.006 |last1=Chatelain|first1=Étienne Hébert|last2=Breton|first2=Sophie|last3=Lemieux|first3=Hélène|last4=Blier|first4=Pierre U.|title=Epitoky in ''Nereis'' (''Neanthes'') ''virens'' (Polychaeta: Nereididae): A story about sex and death |journal=Comparative Biochemistry and Physiology B |volume=149 |issue=2008 |pages=202–208 |year=2008 |pmid=17942355 }}</ref> Typically, male worms undergo a more pronounced transformation from atoke to epitoke. Modifications may include an increase in size of parapodia and the development of paddle-like chaetae for enhanced swimming ability, atrophy of the gut, filling of the body cavity with gametes (eggs or sperm), the development of large eyes, and the musculature may even change to perform swimming movements instead of feeding movements.<ref name="Chatelain" /><ref name="Dorresteign">{{cite book|last1=Dorresteijn|first1=Adriaan W.C.|last2=Westheide|first2=Wilfried|title=Reproductive Strategies and Developmental Patterns in Annelids|year=2013|publisher=Springer Science & Business Media|isbn=9789401728874}}</ref> The majority of species that undergo epigamy are unable to revert to the atoke form and die after reproducing.

Male and female epitokes are produced and swim to the water's surface only at certain times of the year and are often synchronized with moon cycles in a behavior called '''swarming'''. Swarming brings individuals of the same species together so that there is an increased rate of fertilization.<ref>{{cite book|last1=Karleskint|first1=George|last2=Turner|first2=Richard|last3=Small|first3=James|title=Introduction to Marine Biology, Third Edition|year=2009|publisher=Cengage Learning|isbn=9780495561972|pages=237}}</ref> Some polychaete species have been found to use bioluminescence, presumably to compact and maintain swarms.<ref name="Dorresteign" /> Both schizogamous and epigamous epitokes are non-feeding individuals that die once gametes have been released into the water.

In the past, epitokes were thought to be a separate group of polychaete marine worms, because epitokes may look very different than atokes. For instance, the atokes of ''Platynereis dumerilii'' are yellowish-brown, while the female epitokes are yellow because of the eggs they contain, and the male epitokes are white in the front part due to sperm and red in the hind part due to blood vessels<ref>{{cite journal|last1=Fischer|first1=Antje HL|last2=Henrich|first2=Thorsten|last3=Arendt|first3=Detlev|title=The normal development of Platynereis dumerilii (Nereididae, Annelida)|journal=Frontiers in Zoology|date=2010|volume=7|issue=1|pages=31|doi=10.1186/1742-9994-7-31|pmc=3027123|pmid=21192805 |doi-access=free }}</ref> (see pictures).

{{Multiple image | image1 = PlatynereisDumeriliiAtoke.tif | caption1 = Atoke | alt1 = swimming worm, gradienting from a yellow tail to brown head | image2 = PlatynereisDumeriliiFemaleEpitoke.tif | caption2 = Female epitoke; the yellow eggs are evident throughout the body | alt2 = | image3 = PlatynereisDumeriliiMaleEpitoke.tif | caption3 = Male epitoke; front filled with white sperm, and rear is red with blood. | alt3 = | header = Life stages of ''Platynereis dumerilii'' (Nereididae) | perrow = 1/2 | align = center | caption_align = center | footer_align = center | total_width = 450 }}

== References == <references/>

Category:Reproduction in animals Category:Asexual reproduction