ANATOMY

Rotifers come in a diverse variety of shapes and types. In general, the body of a rotifer consists of 3 regions: a head, a trunk and a foot. In most species, the head carries a retractable rostrum and a crown of cilia (corona) bringing water and food to the mouth. The food is grinded by a mastax containing trophi (jaws), a characteristic organ of almost all rotifers located in the pharynx.

Bdelloid rotifer Adineta Vaga (94% water)

Adineta vaga minor Bryce, 1893 [Donner, 1965]

The entire body of rotifers is telescopic and covered by a transparent cuticle. The trunk is mostly filled by the stomach, the reproductive organs and the circular and longitudinal muscles. Rotifers also have a rudimentary nervous and excretory system. The foot contains at the end “toes” with pedal glands secreting a substance that enables a strong adhesion to substrates.

KARINE EXPLAINS ROTIFERS

REPRODUCTION

Different reproductive modes have been described in rotifers. Bdelloid rotifers contain no males and depend entirely on parthenogenesis for their reproduction: unfertilized eggs develop into new females. Whether meiosis is completely absent remains unknown. Most bdelloid species are oviparous, laying eggs. A few species however are viviparous, with embryos developing inside the mother.

In monogonont rotifers, reproduction is through cyclical parthenogenesis. During favorable conditions parthenogenetic reproduction occurs in which unfertilized diploid eggs develop into new asexual females. When a mixis induction cue appears, sexual daughters are produced who form haploid eggs through meiosis. When unfertilized, these haploid eggs develop into males that will fertilize sexual females to produce diploid resting eggs. Resting eggs can survive desiccation and hatch into asexual females. Males of monogonont rotifers are dwarfs with a body mostly filled by the copulatory organ, they are short-living and just producing haploid sperm to fertilize the sexual females.

The third clade within the phylum Rotifera are the Seisonidea, with only two known species. Seisonid rotifers are found only attached to a particular genus of marine crustaceans and are obligately sexual.

It is still debated whether the clade Acantocephala, being endoparasitic, belongs to the Rotifera. Acantocephalans are also obligately sexual.

STRESS

When stressed, most rotifers curl up by retracting their foot.

When experiencing desiccation (absence of water), bdelloid rotifers slowly retract telescopically their body into a tun, lose water and become a compact, metabolically inactive form.

Bdelloid rotifer Adineta Vaga (6,5% water)

Tuns can easily disperse with the wind or attach to birds, being transported over long distances.

Bdelloid species living in extreme environments that dry up frequently (such as deserts) or in frozen habitats (such as Antarctica) will survive for months or years in desiccated tun form.

Upon rehydration they regain an active form and continue their life-cycles.

Bdelloid rotifer Adineta Vaga (6,5% water)

BORIS EXPLAINS ROTIFERS

REFERENCES

Extreme resistance of bdelloid rotifers to ionizing – Eugene Gladyshev and Matthew Meselson

Extreme anti-oxidant protection against ionizing radiation in bdelloid rotifers– Krisko A, Leroy M, Radman M, Meselson M.

Genomic evidence for ameiotic evolution in the bdelloid rotifer Adineta vaga– Jean-François Flot, Boris Hespeels, […], & Karine Van Doninck

Gateway to genetic exchange? DNA double-strand breaks in the bdelloid rotifer Adineta vaga submitted to desiccation– Hespeels B, Knapen M, Hanot-Mambres D, Heuskin AC, Pineux F, Lucas S, Koszul R, Van Doninck K.

Horizontal gene transfer in bdelloid rotifers is ancient, ongoing and more frequent in species from desiccating habitats– Isobel Eyres, Chiara Boschetti, Alastair Crisp, Thomas P. Smith, Diego Fontaneto, Alan Tunnacliffe & Timothy G. Barraclough

Evidence for Ancient Horizontal Gene Acquisitions in Bdelloid Rotifers of the Genus Adineta– – Boris Hespeels, Jean-François Flot, Alessandro Derzelle, Karine Van Doninck

Against All Odds: Trehalose-6-Phosphate Synthase and Trehalase Genes in the Bdelloid Rotifer Adineta vaga Were Acquired by Horizontal Gene Transfer and Are Upregulated during Desiccation – Boris Hespeels, Xiang Li, Jean-François Flot, Lise-Marie Pigneur, Jeremy Malaisse, Corinne Da Silva & Karine Van Doninck

Evidence for meiotic sex in bdelloid rotifers– Ana Signorovitch, Jae Hur, Eugene Gladyshev & Matthew Meselson

Response to Signorovitch et al.– Jean-François Flot, Nicolas Debortoli, Bernard Hallet & Karine Van Doninck

Bdelloid rotifers: ‘sleeping beauties’ and ‘evolutionary scandals’, but not only– Claudia Ricci

Genetic Exchange among Bdelloid Rotifers Is More Likely Due to Horizontal Gene Transfer Than to Meiotic Sex– Nicolas Debortoli, Xiang Li, Isobel Eyres, Diego Fontaneto, Boris Hespeels, Cuong Q.Tang, Jean-François Flot & Karine Van Doninck

Evolutionary diversity and novelty of DNA repair genes in asexual Bdelloid rotifers– Bette J. Hecox-Lea & David B. Mark Welch

The relationship between oxidative stress, reproduction, and survival in a bdelloid rotifer– Leigh C. Latta IV, K. Nathaniel Tucker & Robert A. Haney