Editing Rotifer (section)

==Reproduction and life cycle==
Rotifers are [[dioecious]] and reproduce sexually or [[parthenogenesis|parthenogenetically]]. They are [[sexual dimorphism|sexually dimorphic]], with the females always being larger than the males. In some species, this is relatively mild, but in others the female may be up to ten times the size of the male. In parthenogenetic species, males may be present only at certain times of the year, or absent altogether.<ref name=IZ/>

The female reproductive system consists of one or two [[ovary|ovaries]], each with a ''[[vitellarium]]'' gland that supplies the eggs with [[yolk]]. Together, each ovary and vitellarium form a single [[syncitium|syncitial]] structure in the anterior part of the animal, opening through an [[oviduct]] into the [[cloaca]].<ref name=IZ/>

Males do not usually have a functional digestive system, and are therefore short-lived, often being [[sexually fertile]] at birth. They have a single [[testicle]] and [[sperm duct]], associated with a pair of glandular structures referred to as ''prostates'' (unrelated to the vertebrate [[prostate]]). The sperm duct opens into a [[gonopore]] at the posterior end of the animal, which is usually modified to form a [[penis]]. The gonopore is [[homology (biology)|homologous]] to the cloaca of females, but in most species has no connection to the vestigial digestive system, which lacks an [[anus]].<ref name=IZ/>

In the genus [[Asplanchna]] also the females lacks an anus, but have kept the cloacal opening for excretion and the release of eggs.<ref>{{Cite journal |last=Hejnol |first=Andreas |last2=Martín-Durán |first2=José M. |date=May 2015 |title=Getting to the bottom of anal evolution |url=https://linkinghub.elsevier.com/retrieve/pii/S004452311500011X |journal=Zoologischer Anzeiger - A Journal of Comparative Zoology |language=en |volume=256 |pages=61–74 |doi=10.1016/j.jcz.2015.02.006|hdl=1956/10848 |hdl-access=free }}</ref>

The phylum Rotifera encloses three classes that reproduce by three different mechanisms: Seisonidea only reproduce sexually; Bdelloidea reproduce exclusively by asexual parthenogenesis; Monogononta reproduce alternating these two mechanisms ("cyclical parthenogenesis" or "heterogony").<ref name="Nogrady, T. 1993">Nogrady, T., Wallace, R.L., Snell, T.W., 1993. Rotifera vol.1: biology, ecology and
systematics. Guides to the identification of the microinvertebrates of the continental
waters of the world 4. SPB Academic Publishing bv, The Hague.</ref> Parthenogenesis (amictic phase) dominates the monogonont life cycle, promoting fast population growth and colonization. In this phase males are absent and amictic females produce diploid eggs by mitosis which develop parthenogenetically into females that are clones of their mothers.<ref name="Nogrady, T. 1993"/> Some amictic females can generate mictic females that will produce haploid eggs by meiosis. Mixis (meiosis) is induced by different types of stimulus depending on species. Haploid eggs develop into haploid dwarf males if they are not fertilized and into diploid "resting eggs" (or "diapausing eggs") if they are fertilized by males.

Fertilization is internal. The male either inserts his penis into the female's cloaca or uses it to penetrate her skin, injecting the sperm into the body cavity. The egg secretes a shell, and is attached either to the substratum, nearby plants, or the female's own body. A few species, such as members of the ''[[Rotaria]]'', are [[ovoviviparous]], retaining the eggs inside their body until they hatch.<ref name=IZ/>

Most species hatch as miniature versions of the adult. Sessile species, however, are born as free-swimming [[larva]]e, which closely resemble the adults of related free-swimming species. Females grow rapidly, reaching their adult size within a few days, while males typically do not grow in size at all.<ref name=IZ/>

The life span of [[Monogononta|monogonont]] females varies from two days to about three weeks.

===Loss of sexual reproduction system===
''''Ancient asexuals':''' [[Bdelloid]] rotifers are assumed to have reproduced without sex for many millions of years. Males are absent within the species, and females reproduce only by [[parthenogenesis]].

However, a new study provided evidence for interindividual genetic exchange and recombination in ''[[Adineta]] vaga'', a species previously thought to be anciently asexual.<ref>{{cite journal |author=Vakhrusheva, O.A. |author2=Mnatsakanova, E.A. |author3=Galimov, Y.R. |display-authors=etal|title=Genomic signatures of recombination in a natural population of the bdelloid rotifer Adineta vaga |date=18 December 2020|journal=Nature|volume=11 |issue=1 |page=6421 |doi=10.1038/s41467-020-19614-y |pmid=33339818 |pmc=7749112 |bibcode=2020NatCo..11.6421V }}</ref>

'''Recent transitions:''' Loss of [[sexual reproduction]] can be inherited in a simple [[Mendelian inheritance|Mendelian fashion]] in the monogonont rotifer ''[[Brachionus calyciflorus]]'': This species can normally switch between sexual and asexual reproduction (cyclical parthenogenesis), but occasionally gives rise to purely asexual lineages (obligate parthenogens). These lineages are unable to reproduce sexually due to being homozygous for a recessive allele.<ref>{{cite journal |author=Claus-Peter Stelzer |author2=Johanna Schmidt |author3=Anneliese Wiedlroither |author4=Simone Riss |date=20 September 2010 |title=Loss of sexual reproduction and dwarfing in a small metazoan |journal=[[PLoS ONE]] |volume=5 |issue=9 |pages=e12854 |doi=10.1371/journal.pone.0012854 |pmid=20862222 |pmc=2942836|bibcode=2010PLoSO...512854S |doi-access=free }}</ref>

===Resting eggs===
Resting eggs enclose an embryo encysted in a three-layered shell that protects it from external stressors.<ref>{{cite journal |last1=Wurdak |first1=Elizabeth S. |last2=Gilbert |first2=John J. |last3=Jagels |first3=Richard |title=Fine Structure of the Resting Eggs of the Rotifers Brachionus calyciflorus and Asplanchna sieboldi |journal=Transactions of the American Microscopical Society |date=January 1978 |volume=97 |issue=1 |pages=49–72 |pmid=564567 |jstor=3225684 |doi=10.2307/3225684 }}</ref><ref>{{cite book |last1=Clément |first1=P. |last2=Wurdak |first2=E. |year=1991 |chapter=Rotifera |editor1-last=Harrison |editor1-first=F.W. |editor2-last=Ruppert |editor2-first=E.E. |title=Microscopic Anatomy of Invertebrates |series=Aschelminthes, vol. IV |publisher=Wiley-Liss |pages=219–97 }}</ref> They are able to remain dormant for several decades and can resist adverse periods (e.g., pond desiccation or presence of antagonists).<ref>{{cite journal |last1=Marcus |first1=Nancy H. |last2=Lutz |first2=Robert |last3=Burnett |first3=William |last4=Cable |first4=Peter |title=Age, viability, and vertical distribution of zooplankton resting eggs from an anoxic basin: Evidence of an egg bank |journal=Limnology and Oceanography |date=January 1994 |volume=39 |issue=1 |pages=154–158 |doi=10.4319/lo.1994.39.1.0154 |bibcode=1994LimOc..39..154M |doi-access=free }}</ref><ref>{{cite book |doi=10.1007/978-94-010-0756-6_37 |chapter=Reproductive isolation among geographically and temporally isolated marine Brachionus strains |title=Rotifera IX |pages=283–290 |year=2001 |last1=Kotani |first1=T. |last2=Ozaki |first2=M. |last3=Matsuoka |first3=K. |last4=Snell |first4=T. W. |last5=Hagiwara |first5=A. |isbn=978-94-010-3820-1 }}</ref> When favourable conditions return and after an obligatory period of [[diapause]] which varies among species, resting eggs hatch releasing diploid amictic females that enter into the asexual phase of the life cycle.<ref name="Nogrady, T. 1993"/><ref>{{cite journal |last1=García-Roger |first1=Eduardo M. |last2=Carmona |first2=María José |last3=Serra |first3=Manuel |title=Deterioration patterns in diapausing egg banks of Brachionus (Müller, 1786) rotifer species |journal=Journal of Experimental Marine Biology and Ecology |date=January 2005 |volume=314 |issue=2 |pages=149–161 |doi=10.1016/j.jembe.2004.08.023 |bibcode=2005JEMBE.314..149G }}</ref>

===Anhydrobiosis===
Bdelloid rotifer females cannot produce resting eggs, but many can survive prolonged periods of adverse conditions after [[desiccation]]. This facility is termed [[anhydrobiosis]], and organisms with these capabilities are termed anhydrobionts. Under drought conditions, bdelloid rotifers contract into an inert form and lose almost all body water; when rehydrated they resume activity within a few hours. Bdelloids can survive the dry state for long periods, with the longest well-documented dormancy being nine years. Rotifers can also undergo other forms of cryptobiosis, notably cryobiosis which results from decreased temperatures. In 2021, researchers collected  samples from remote Arctic locations containing rotifers which when thawed revealed living specimens around 24,000 years old.<ref>{{Cite journal |last1=Shmakova |first1=Lyubov |last2=Malavin |first2=Stas |last3=Iakovenko |first3=Nataliia |last4=Vishnivetskaya |first4=Tatiana |last5=Shain |first5=Daniel |last6=Plewka |first6=Michael |last7=Rivkina |first7=Elizaveta |date=June 2021 |title=A living bdelloid rotifer from 24,000-year-old Arctic permafrost |journal=Current Biology |volume=31 |issue=11 |pages=R712–R713 |doi=10.1016/j.cub.2021.04.077 |s2cid=235365588 |issn=0960-9822|doi-access=free |pmid=34102116 |bibcode=2021CBio...31.R712S }}</ref> While in other anhydrobionts, such as the [[brine shrimp]], this desiccation tolerance is thought to be linked to the production of [[trehalose]], a non-reducing disaccharide ([[sugar]]), bdelloids apparently cannot synthesise trehalose. In bdelloids, a major cause of the resistance to desiccation, as well as resistance to ionizing radiation, is a highly efficient mechanism for repairing the DNA double-strand breaks induced by these agents.<ref name="pmid25105197">{{cite journal |vauthors=Hespeels B, Knapen M, Hanot-Mambres D, Heuskin AC, Pineux F, LUCAS S, Koszul R, Van Doninck K |title=Gateway to genetic exchange? DNA double-strand breaks in the bdelloid rotifer Adineta vaga submitted to desiccation |journal=J. Evol. Biol. |volume=27 |issue=7 |pages=1334–45 |date=July 2014 |pmid=25105197 |doi= 10.1111/jeb.12326|url=https://hal-pasteur.archives-ouvertes.fr/pasteur-01420001/file/hespeels%20et%20al%202014.pdf|doi-access=free }}</ref> This repair mechanism likely involves mitotic recombination between homologous DNA regions.<ref name="pmid25105197" />