Rotifers Research Articles

Oocyte nuclear DNA content and GC proportion in rotifers of the anciently asexual Class Bdelloidea

The approximately 360 species of the Class Bdelloidea (Phylum Rotifera) constitute the largest, most diverse and oldest eukaryotic group for which obligate asexuality has morphological, cytological and molecular support. DNA sequence studies indicate that the class constitutes a single clonal lineage, 50-100 million years old. Here we report cytofluorometric measurements of oocyte nuclear DNA content and GC proportion for six bdelloid species, representing the three major families of Bdelloidea. We find wide differences between species in nuclear DNA content (0.5-2.4 pg) and proportion of GC (37-57%). The proportion of GC in the nuclear DNA of all six species is greater than that in their coding regions examined to date, and tends to be greater in species with greater nuclear DNA content. Interspecific differences in nuclear DNA content do not correlate with chromosome numbers, which range from 10 to 13, and are therefore not due to differences in ploidy. In addition, since bdelloids seemingly lack functional reverse transcriptase genes, the observed interspecific differences in nuclear DNA content and GC proportion do not appear to have resulted from retrotransposon activity. The values of oocyte nuclear DNA content obtained by cytofluorometric measurement are close to the values of total genome size we previously obtained from measurements of DNA hybridization intensity, indicating that bdelloid genomes do not undergo significant somatic chromatin diminution and, unlike the genomes of sexually reproducing diploids or polyploids, do not consist of two or more nearly identical haplotypes.

Evolution of rotifers in saline and subsaline lakes: A molecular phylogenetic approach

Evolutionary relationships within the phylum Rotifera are poorly understood despite the important role that they play in freshwater ecosystems. Phylogenetic analyses of DNA sequences from two mitochondrial genes, 16S rDNA and cytochrome oxidase I (COI), were employed to examine the extent of genetic divergence within populations of several common taxa. This work sought to verify the role of phenotypic plasticity versus genetic variation in explaining the morphological variation in some taxa. Deep genetic divergence (4.4% COI nucleotide sequence divergence) was detected between spined and unspined forms of Keratella cochlearis, which suggests that they represent different species. However, morphological variation in K. hiemalis appeared to be environmentally induced. The study also sought to ascertain the role of one environmental variable, salinity, in the patterning of sequence variation. Greater haplotype diversity and genetic divergence were observed among populations of halophilic Brachionus plicatilis than among freshwater Keratella quadrata populations from northern Canada. When COI DNA sequences for B. plicatilis haplotypes were compared with those from Spain, there was evidence for considerable genetic diversity within this species among closely located saline lakes in northern Canada.

Bdelloid rotifers (Rotifera, Bdelloidea) as a component of soil and land biocenoses

Morphological, physiological, and ecological adaptations of bdelloid rotifers (phylum Rotifera, class Bdelloidea) to the conditions of soil and land biocenoses are presented. The morphological structures, obligate parthenogenesis, and anhydrobiosis allowed these rotifers to colonize various semiaquatic areas with sharp fluctuations of environmental conditions: edaphon, coniferous and deciduous litters, mosses, and lichens. The role of bdelloid rotifers in the food web and environmental indication was mentioned. The controversial problems of the origin of this group of worms were broached.

Mediterranean Rotifers: a very inconspicuous taxon

Biogeographia vol. XXIV - 2003 (Printed October, 31 st 2003) Marine biogeography of the Mediterranean Sea: patterns and dynamics of biodiversity Mediterranean Rotifers: a Very inconspicuous taxon CLAUDM RICCI, DIEGO FONTANETO Universziiz Stamle zli Milzmo, Dz'}7zzrtz'mem‘0 dz‘ Biolagia, Via Celoria 26, I—20]33 Milano (Italy) Key words: Rotifera, Mediterranean Sea, marine rotifers. SUMMARY Occurrence of rotifer species in the sea is here reviewed, with emphasis on the Mediterranean Sea. Most of the few investigations dealt with rorifer species in Arctic and Antarctic Seas and along Northern European coasts, while Mediterranean area has received very little attention. Despite the few studies, one hundred five rotifers are reported as strictly marine, of these only 20 are signaled in the Mediterranean Sea. The species number is doubled if the freshwater rotifers that are occasionally found in the sea are added. Reasonably, the short list of rotifers from the Mediterranean is to be ascribed to the very few studies carried out and not to absence of rotifers in the area. ROTIFERS Phylum Rotifera comprises 1800 species of microscopic metazoans (80—2000um in length) divided into three major groups: Monogononta (~1450 species), Bdelloidea (~350) and Seisonidea (2) (Segers, 2002). They are characterized by short life cycle and direct development, most are filter-feeders, some are predators and few live as parasites. The three groups differ because of their reproduction. Seisonids are always amphimictic, with sex ratio 1:1, and monogononts punctuate thelytokous parthenogenesis (producing females) with arrhenotokous parthenogenesis (producing males) and subsequent sexual reproduction. Mating produces a diploid egg with delayed development, called resting egg; however, among most monogonont species only females are known so far. Bdelloids consist of parthenogenetic females only (Mark Welch and Meselson, 2000). Monogononts live in aquatic habitats like rivers, lakes, ponds, temporaiy and permanent pools, lagoons and seas, and very few can live in the water films around soil particles (Nogrady et al., 1993). Bdelloids are commonly part of the meiofauna of any habitat where Water is occasionally present, thus they can be found in rivers, lakes, ponds, but also among soil particles, and in mosses and lichens (Donner,

Rotifera fauna of Asi (Orontes) River (Hatay, Turkey).

Rotifera fauna of Asi (Orontes) River (Hatay, Turkey).

Large scale rotifer cultures.

large scale rotifer cultures.

Rates of nucleotide substitution in sexual and anciently asexual rotifers

The class Bdelloidea of the phylum Rotifera is the largest well studied eukaryotic taxon in which males and meiosis are unknown, and the only one for which these indications of ancient asexuality are supported by cytological and molecular genetic evidence. We estimated the rates of synonymous and nonsynonymous substitutions in the hsp82 heat shock gene in bdelloids and in facultatively sexual rotifers of the class Monogononta, employing distance based and maximum likelihood methods. Relative-rate tests, using acanthocephalan rotifers as an outgroup, showed slightly higher rates of nonsynonymous substitution and slightly lower rates of synonymous substitution in bdelloids as compared with monogononts. The opposite trend, however, was seen in intraclass pairwise comparisons. If, as it seems, bdelloids have evolved asexually, an equality of bdelloid and monogonont substitution rates would suggest that the maintenance of sexual reproduction in monogononts is not attributable to an effect of sexual reproduction in limiting the load of deleterious nucleotide substitutions.

Effect of three food types on the population growth of Brachionus calyciflorus and Brachionus patulus (Rotifera: Brachionidae).

We compared the population growth of B. calyciflorus and B. patulus using the green alga Chlorella vulgaris, baker's yeast Saccharomyces cerevisiae or their mixture in equal proportions as food. Food was offered once every 24 h in two concentrations (low: 1 x 10(6) and high: 3 x 10(6) cells ml-1) separately for each species. The experiments were terminated after 15 days. In general, at any food type or concentration, B. patulus reached a higher population density. A diet of Chlorella alone supported a higher population growth of both rotifer species than yeast alone. B. calyciflorus and B. patulus achieved highest population densities (103 +/- 8 ind. ml-1 and 296 +/- 20 ind. ml-1, respectively) on a diet of Chlorella at 3 x 10(6) cells ml-1. When cultured using the mixture of Chlorella and yeast, the maximal population densities of B. calyciflorus were lower than those grown on Chlorella. Under similar conditions, the maximal abundance values of B. patulus were comparable in both food types. Regardless of food type and density the rate of population increase per day (r) for B. calyciflorus varied from 0.13 +/- 0.03 to 0.63 +/- 0.04. These values for B. patulus ranged from 0.19 +/- 0.01 to 0.37 +/- 0.01. The results indicated that even though Chlorella was a superior food for the tested rotifers, yeast can be effectively used at low concentrations to supplement algal requirements in rotifer culture systems.

Feeding Ecology of Three Omnivorous Fishes in Lake Texoma (Oklahoma-Texas)

Feeding Ecology of Three Omnivorous Fishes in Lake Texoma (Oklahoma-Texas)

New records of rotifera for the Cameroon fauna from Korup Park and its environs

New records of rotifera for the Cameroon fauna from Korup Park and its environs

Predation of Paradileptus elephantinus on rotifers

Predation of <i>Paradileptus elephantinus</i> on rotifers

Performance of 18S rDNA helix E23 for phylogenetic relationships within and between the Rotifera–Acanthocephala clades

The species diversity of the phylum Rotifera has been largely studied on the basis of morphological characters. However, cladistic relationships within this group are poorly resolved due to extensive homoplasy in morphological traits, substantial phenotypic plasticity and a poor fossil record. We undertook this study to determine if a phylogeny based on partial 18S rDNA, which included the helix E23 of 18S rDNA sequence, was concordant with established taxonomic relationships within the order Ploimida (class: Monogononta). We also estimated the level of polymorphism within clones and populations of Ploimida ‘species’. Finally, we included the Cycliophora Symbion pandora as outgroup and the variable helix E23 region to examine the influence of their signal on the evolutionary relationships among Acanthocephala, Bdelloidea and Ploimida. Phylogenetic reconstruction was performed using maximum parsimony, neighbour joining and maximum likelihood methods. We found 1) that morphologically similar Ploimida ‘species’ show vastly different 18S E23 rDNA sequences; 2) inclusion of the helix E23 of 18S rDNA and its secondary structure analysis results in better resolution of family level relationships within the Ploimida; 3) an impact of Symbion pandora as an outgroup with inclusion of the helix E23 on the relationships between the Rotifera and the Acanthocephala; and 4) partial incongruence and differential substitution rate between conserved region and helix E23 region of the 18S rDNA gene depending on the taxomic group studied.

Evidence for the evolution of bdelloid rotifers without sexual reproduction or genetic exchange.

The Class Bdelloidea of the Phylum Rotifera is the largest metazoan taxon in which males, hermaphrodites, and meiosis are unknown. We conducted a molecular genetic test of this indication that bdelloid rotifers may have evolved without sexual reproduction or genetic exchange. The test is based on the expectation that after millions of years without these processes, genomes will no longer contain pairs of closely similar haplotypes and instead will contain highly divergent descendants of formerly allelic nucleotide sequences. We find that genomes of individual bdelloid rotifers, representing four different species, appear to lack pairs of closely similar sequences and contain representatives of two ancient lineages that began to diverge before the bdelloid radiation many millions of years ago when sexual reproduction and genetic exchange may have ceased.

Control ofVolvoxblooms byHertwigia, a rotifer

(1998). Control of Volvox blooms by Hertwigia, a rotifer. SIL Proceedings, 1922-2010: Vol. 26, No. 4, pp. 1781-1784.

A comparative study of trophi morphology in Seisonidea (Rotifera)

AbstractWe report on a comparative scanning electron microscopical study of trophi morphology of the two species making up the Class Seisonidea of Phylum Rotifera. The trophi of the two are generally similar, with morphological differences being interpreted as the result of adaptations to different food sources: the trophi of Seison nebaliae are adapted to particle‐feeding, that of Seison annulatus probably functions by piercing the integument of the host using the fulcrum tip, and subsequently sucking out haemolymph. This difference in feeding ecology is believed to contribute to the co‐occurrence of both species on the same host. A new hypothesis on the evolution of rotifer trophi is proposed.

Molecular evidence for Acanthocephala as a subtaxon of Rotifera

Rotifers are free-living animals usually smaller than 1 mm that possess a characteristic wheel organ. Acanthocephalans (thorny-headed worms) are larger endoparasitic animals that use vertebrates and arthropods to complete their life cycle. The taxa Acanthocephala and Rotifera are considered separate phyla, often within the taxon Aschelminthes. We have reexamined the relationship between Rotifera and Acanthocephala using 18S rRNA gene sequences. Our results conclusively show that Acanthocephala is the sister group of the rotifer class Bdelloidea. Rotifera was nonmonophyletic in all molecular analyses, which supports the hypothesis that the Acanthocephala represent a taxon within the phylum Rotifera and not a separate phylum. These results agree with a previous cladistic study of morphological characters.

Fungi which attack rotifers

Fungi which attack rotifers

Relation to habitat in rotifers

Relation to habitat in rotifers

Additions to the Checklist of Rotifers of the Superorder Monogononta Recorded from Neotropis

Additions to the Checklist of Rotifers of the Superorder Monogononta Recorded from Neotropis

Unpalatability of a Colonial Rotifer, Sinantherina socialis, to Small Zooplanktivorous Fishes

Colonies of Sinantherina socialis (phylum Rotifera) form conspicuous masses that should make them extremely vulnerable to fishes capable of ingesting small live prey (<3 mm in length). To test this hypothesis we offered rotifer colonies as prey to 14 species of smallmouthed, predatory fishes, alternating with small cladocerans. Most rotifer colonies (71-100%), but few cladocerans (0-14%) were rejected after capture. Fish feeding behavior on rotifers followed a consistent pattern: locate, approach, attack, mouth repeatedly, and reject (spit out). Except for loss of a few individuals, rotifer colonies that had been repeatedly rejected remained undamaged. This is the first evidence for unpalatability of rotifers to zooplanktivorous fishes. Additional key words: fish feeding, Flosculariidae, Monogononta, predation, predatory defense, Rotifera, unpalatability, zooplanktivory Rotifers (about 100-1000 |jm) fall prey to a variety of tactile invertebrate predators such as other rotifers, insect larvae, and microand macrocrustaceans (Williamson 1983; Stemberger & Gilbert 1987). They also are an excellent food source for marine and freshwater fish larvae (Newrkla & Duncan 1984; Lubzens 1987; Lubzens et al. 1989). Larval fishes may feed extensively on rotifers (Landau et al. 1988), even when alternate prey are available (Hewitt & George 1987; Zale & Gregory 1990). Thus, rotifers are caught between the two millstones of tactile and visual predation; there is no refuge from zooplanktivorous fishes other than preserving a small body size, which maintains susceptibility to many tactile predators. One defense against tactile predators used by rotifers appears to be the formation of colonies, at least in those species that produce a gelatinous matrix (e.g., Conochilidae REMANE 1933). For those species the jelly mass provides a refuge into which the rotifers may retract when attacked (Gilbert 1980). However, colony formation in rotifers increases effective size by several fold, placing the colonies within a size range consumable by small zooplanktivorous fishes or their larvae: 0.8 to 4 mm (Siefert 1972; Crecco & Blake 1983; O'Brien & Evans 1991). Therefore, it seems plausible that colonial rotifers should be present in habitats where predation by tactile predators is more intense than by visual predators. Of course, colony formation may have other consequences, such as increasing the a To whom correspondence should be addressed. efficiency of water flow over a group of closely spaced individuals engaged in suspension feeding (see Wallace 1987 for a review). Of 8 rotifer genera with colonial species, the genus Sinantherina BORY DE ST. VINCENT 1826 (Monogononta, Flosculariidae) is particularly interesting because sinantherinids do not possess the gelatinous matrix that is characteristic of the family and many species form colonies so large and conspicuous that they are easily seen from above the water surface. For example, two sinantherinids produce pelagic juveniles with adult colonies that are sessile on aquatic plants: S. ariprepes EDMONDSON 1939 (Edmondson 1940), S. socialis (LINNAEUS 1758) (Surface 1906; Wallace 1987). A third sinantherinid is holoplanktonic in shallow waters, S. semibullata (THORPE 1889) (Canella 1952; Gunter & Knight 1978). As a consequence of these features, one might expect that sinantherinids would be extraordinarily vulnerable to fish predation, yet they are often present in habitats with small, predatory fishes (R. Wallace, unpubl. obs.). How do these colonial rotifers avoid extirpation by fishes? Kerfoot and his co-workers have demonstrated that many conspicuous aquatic arthropods (insects and hydracarinids) have chemical defenses (e.g., steroids) against predation by fishes (Kerfoot et al. 1980; Kerfoot 1982; Scrimshaw & Kerfoot 1987). Extrapolating from that work, one of us (Wallace 1987) suggested that colonies of S. socialis might possess chemical defenses rendering them unpalatable to zooplanktivorous fishes. Here we describe a test of a simpler hypothesis: This content downloaded from 157.55.39.153 on Mon, 19 Sep 2016 04:42:00 UTC All use subject to http://about.jstor.org/terms Felix, Stevens, & Wallace that colonies of S. socialis are unpalatable to predatory fishes and will be preyed upon at lower rates than will other small live prey.