Ultrastructure of the extraordinary pedal gland in Asplanchna aff. herricki (Rotifera: Monogononta).

Rotifers possess complex morphologies despite their microscopic size and simple appearance. Part of this complexity is hidden in the structure of their organs, which may be cellular or syncytial. Surprisingly, organs that are cellular in one taxon can be syncytial in another. Pedal glands are widespread across Rotifera and function in substrate attachment and/or egg brooding. These glands are normally absent in Asplanchna, which lack feet and toes that function as outlets for pedal glandular secretions in other rotifers. Here, we describe the ultrastructure of a pedal gland that is singular and syncytial in Asplanchna aff. herricki, but is normally paired and cellular in all other rotifers. Asplanchna aff. herricki has a single large pedal gland that is active and secretory; it has a bipartite, binucleate, syncytial body and a cytosol filled with rough endoplasmic reticulum, Golgi, and several types of secretory vesicles. The most abundant vesicle type is large and contains a spherical electron-dense secretion that appears to be produced through homotypic fusion of condensing vesicles produced by the Golgi. The vesicles appear to undergo a phase transition from condensed to decondensed along their pathway toward the gland lumen. Decondensation changes the contents to a mucin-like matrix that is eventually exocytosed in a "kiss-and-run" fashion with the plasma membrane of the gland lumen. Exocytosed mucus enters the gland lumen and exits through an epithelial duct that is an extension of the syncytial integument. This results in mucus that extends from the rotifer as a long string as the animal swims through the water. The function of this mucus is unknown, but we speculate it may function in temporary attachment, prey capture, or floatation.

To what extent are ephippia of Mexican Anomopoda (Crustacea, Cladocera) identifiable?

Diapausing embryos encased within cladoceran ephippia result from sexual reproduction and increase genetic diversity. They are also important means by which species bypass harsh environmental conditions and disperse in space and time. Once released, ephippia usually sink to the benthos and remain there until hatching. Using the Sars' method (incubating sediments to identify cladoceran hatchlings), ephippial egg bank biodiversity can be evaluated. Yet, even when samples are incubated under a variety of conditions, it is not possible to warrant that all have hatched. Few keys are available that facilitate the identification of cladocerans by using only ephippial morphology. Our goal was to analyze some cladoceran ephippia from Mexico, to develop a means to identify them using easily recognizable characteristics. Ephippia of 23 cladoceran species from waters in Aguascalientes (México) in 11 genera (Alona, Biapertura, Ceriodaphnia, Chydorus, Daphnia, Dunhevedia, Ilyocryptus, Macrothrix, Moina, Pleuroxus, and Simocephalus) were analyzed. In our analysis six morphological features were selected that permitted the identification of ephippia to species(-group) level. The results demonstrate that with a proper catalog of features, some ephippia can be identified.

Key to sessile gnesiotrochan rotifers: Families, monospecific species in Flosculariidae, species of Atrochidae, Conochilidae, and Limnias.

Accurate identification of species is key to understanding their ecological roles and evolutionary history. It is also essential in cataloging biodiversity for comparisons among habitat types, responses to climate change, effective management practices, and more. The paucity of taxonomic expertise is increasing and with it the ability to competently identify species, this is particularly true for small taxa including rotifers. In an effort to improve this situation, we collated information on morphological characters from the literature on all valid species of sessile Gnesiotrocha (phylum Rotifera) currently assigned to two orders and four families. We review Order Collothecaceae, which comprises families Atrochidae (3 spp.) and Collothecidae (50 spp.) and Order Flosculariaceae, which includes families Conochilidae (7 spp.) and Flosculariidae (71 species). Based on that information, we provide dichotomous keys to the Families, monospecific species in Flosculariidae, and species of Atrochidae, Conochilidae, and Limnias. These keys will aid researchers to identify species in these families and lead to a better understanding of freshwater biodiversity and eco-evolutionary processes.

Ultrastructural characterization of the putative defensive glands (warts) in the sessile, colonial rotifer Sinantherina socialis (Gnesiotrocha; Flosculariidae).

Female Sinantherina socialis are freshwater, sessile, colonial rotifers that possess two pairs of distinctive glands (warts) located below the corona. Previous studies demonstrated that colonies are unpalatable to many invertebrate and vertebrate predators; those authors suggested that the warts were a possible source of a chemical deterrent to predation. Here we explore wart ultrastructure and cytochemisty to determine whether the warts function as exocrine glands and if their contents display any allomone-like chemistry, respectively. Externally, the warts appear as elevated bulges without pores. Internally, the warts are specialized regions of the integumental syncytium and therefore acellular. The lipid stain Nile Red labels all four warts. Two lipid membrane probes (sphingomyelin and phosphatidylinositol) also bind the warts and may be staining internal secretion vesicle membranes. In fact, wart ultrastructure is defined by hundreds of membrane-bound secretion vesicles packed tightly together. The vesicles are mostly electron-lucent and crowded into a well-defined cytoplasmic space. The cytoplasm also contains abundant ribosomes, rough endoplasmic reticulum, mitochondria, and Golgi, but nuclei are generally positioned peripheral to the packed vesicles. Absence of muscles around the warts or any signs of direct innervation suggests expulsion of gland contents is forced by general body contraction. A single specimen with 'empty' warts implies that secretions are released en masse from all glands simultaneously. The identity of the chemical secretion remains to be determined, but the lack of osmium and uranyl acetate staining suggests a low abundance or absence of phenols, unsaturated lipids, or NH2 and -COOH groups. This absence, combined with the positive Nile Red staining, is interpreted as evidence that vesicles contain saturated fatty acids such as lactones that are unpalatable to predators.

Fine structure of the subitaneous eggshell of the sessile rotifer Stephanoceros millsii (Monogononta) with observations on vesicle trafficking in the integument during ontogeny.

Rotifers that engage in cyclical parthenogenesis produce two types of eggs: subitaneous eggs that hatch as clonal females and meiotic eggs that hatch as haploid males, or if fertilized, as females after a period of diapause (resting eggs). The ultrastructure of resting eggshells is known for some motile species, but there are limited data on subitaneous eggshells, and no data on any eggshells of sessile rotifers. Here, we investigated the ultrastructure of the subitaneous eggshell of the sessile rotifer Stephanoceros millsii and its potential origins of secretion, the maternal vitellarium and embryonic integument. We also explored secretory activity in the larval and adult integuments to determine whether activity changes during ontogeny. The eggshell consists of a single layer with two sublayers: an external granular sublayer apparently derived from the maternal vitellarium, and an internal flocculent sublayer secreted by the embryonic integument that may form a hatching membrane or glycocalyx. Secretory activity remains high in both the larva and adult and appears to be the source of the thickening glycocalyx. Altogether, the subitaneous eggshell of S. millsii is the thinnest among monogonont rotifers. Thin eggshells may have evolved in response to the added protection provided by the mother's extracorporeal tube.

Limnological Characteristics and Rotifer Community Composition of Northern Mexico Chihuahuan Desert Springs.

Desert springs are critical for wildlife and human subsistence, but poorly studied. The springs in the northern Chihuahuan Desert region of Mexico are no exception. While groundwater overexploitation and other anthropogenic activities have endangered these waters, little is known about their water quality or biodiversity. We monitored five springs on a monthly basis for one year, and two others sporadically, to determine their physicochemical characteristics and to study rotifer community composition as an assessment of biodiversity. Seasonal variation in temperature, dissolved oxygen (DO), and conductivity was observed in the five springs. DO was occasionally below the criterion for aquatic life (<4mg/L) in some springs. Ca2+ (468-775.2 mg/L) was the dominant ion in all springs except Ojo de Santa María where Na+ (180-290 mg/L) dominated. Of 57 rotifer species identified, Lepadella patella (Müller, 1786), Lepadella triptera (Ehrenberg, 1830), and Philodina megalotrocha, Ehrenberg, 1832 were present in most springs. The rotifer community exhibited nestedness among the sites (supported by four null modes, p<0.05) and was correlated with fall season, DO, and nitrate concentration. This work provides information that will aid in management practices and provide important baseline data on water quality and regional diversity of a major component of the zooplankton.

Evidence supporting cryptic species within two sessile microinvertebrates, Limnias melicerta and L. ceratophylli (Rotifera, Gnesiotrocha).

Microorganisms, including rotifers, are thought to be capable of long distance dispersal. Therefore, they should show little population genetic structure due to high gene flow. Nevertheless, substantial genetic structure has been reported among populations of many taxa. In rotifers, genetic studies have focused on planktonic taxa leaving sessile groups largely unexplored. Here, we used COI gene and ITS region sequences to study genetic structure and delimit cryptic species in two sessile species (Limnias melicerta [32 populations]; L. ceratophylli [21 populations]). Among populations, ITS region sequences were less variable as compared to those of the COI gene (ITS; L. melicerta: 0-3.1% and L. ceratophylli: 0-4.4%; COI; L. melicerta: 0-22.7% and L. ceratophylli: 0-21.7%). Moreover, L. melicerta and L. ceratophylli were not resolved in phylogenetic analyses based on ITS sequences. Thus, we used COI sequences for species delimitation. Bayesian Species Delimitation detected nine putative cryptic species within L. melicerta and four putative cryptic species for L. ceratophylli. The genetic distance in the COI gene was 0-15.4% within cryptic species of L. melicerta and 0.5-0.6% within cryptic species of L. ceratophylli. Among cryptic species, COI genetic distance ranged 8.1-21.9% for L. melicerta and 15.1-21.2% for L. ceratophylli. The correlation between geographic and genetic distance was weak or lacking; thus geographic isolation cannot be considered a strong driver of genetic variation. In addition, geometric morphometric analyses of trophi did not show significant variation among cryptic species. In this study we used a conservative approach for species delimitation, yet we were able to show that species diversity in these sessile rotifers is underestimated.

Estrogen alone and health outcomes in black women by African ancestry: a secondary analyses of a randomized controlled trial.

OBJECTIVE: In postmenopausal black women in the Women's Health Initiative randomized trial, estrogen alone reduced breast cancers but its comprehensive influence on health outcomes in black women is unknown. Therefore, we examined this issue in the Women's Health Initiative overall and by African ancestry. METHODS: A total of 1,616 black women with prior hysterectomy, including 1,061 with percent African ancestry determination, at 40 US centers were randomly assigned to conjugated equine estrogen (0.625 mg/d) or placebo for 7.2 years' (median) intervention with 13 years' cumulative follow-up. Coronary heart disease (CHD) and breast cancer were primary efficacy and safety outcomes, respectively. A global index also included stroke, colorectal cancer, hip fracture, pulmonary embolism, and death. RESULTS: Black women in the estrogen-alone group compared with black women in the placebo group had fewer breast cancers (17 vs 40, hazard ratio [HR] 0.47, 95% CI 0.26-0.82). In women with more than 80% African ancestry, breast cancer HR was lower (0.32, 95% CI 0.12-0.86, trend P = 0.04 for ancestry effect). Most other outcomes including CHD, stroke, hip fracture, and the global index were null with estrogen use in black women; a global index effect was more favorable in younger black women (HR 0.65, 95% CI 0.43-0.98). CONCLUSIONS: In black postmenopausal women with prior hysterectomy, estrogen alone significantly reduced breast cancer incidence with no adverse influence on CHD, venous thromboembolism, or all-cause mortality. Favorable estrogen-alone global index effects in younger black women warrant further study.

Period of public commentary begins on the revised proposal of species-group level names, and on the proposal of genus-group level names of the Candidate Part of List of Available Names (LAN) in the phylum Rotifera.

Following ICZN (1999) Article 79 Chapter 17 http://www.nhm.ac.uk/hosted-sites/iczn/code/), we, with the full support of the international community of rotifer researchers as expressed during subsequent international Rotifera symposia, developed a Candidate Part of the List of Available Names for species and genera of Rotifera from the start of zoological nomenclature to the year 2000.

A Rotifer-Based Technique to Rear Zebrafish Larvae in Small Academic Settings.

Raising zebrafish from larvae to juveniles can be laborious, requiring frequent water exchanges and continuous culturing of live feed. This task becomes even more difficult for small institutions that do not have access to the necessary funding, equipment, or personnel to maintain large-scale systems usually employed in zebrafish husbandry. To open this opportunity to smaller institutions, a cost-efficient protocol was developed to culture Nannochloropsis to feed the halophilic, planktonic rotifer Brachionus plicatilis; the rotifers were then used to raise larval zebrafish to juveniles. By using these methods, small institutions can easily raise zebrafish embryos in a cost-efficient manner without the need to establish an extensive fish-raising facility. In addition, culturing rotifers provides a micrometazoan that serves as a model organism for teaching and undergraduate research studies for a variety of topics, including aging, toxicology, and predator-prey dynamics.

Soft Bodies, Hard Jaws: An Introduction to the Symposium, with Rotifers as Models of Jaw Diversity.

Jaws have evolved numerous times in the animal kingdom and they display a wide variety of structural, compositional, and functional characteristics that reflect their polyphyletic origins. Among soft-bodied invertebrates, jaws are known from annelids, chaetognaths, flatworms, gnathostomulids, micrognathozoans, mollusks, rotifers, and several ecdysozoans. Depending on the taxon, jaws may function in the capture of prey (e.g., chaetognaths and flatworms), processing of prey (e.g., gnathostomulids and onychophorans), or both (e.g., rotifers). Although structural diversity among invertebrates' jaws is becoming better characterized with the use of electron microscopy, many details remain poorly described, including neuromuscular control, elemental composition, and physical characteristics, such as hardness and resistance to wear. Unfortunately, absence of relevant data has impeded understanding of their functional diversity and evolutionary origins. With this symposium, we bring together researchers of disparately jawed taxa to draw structural and mechanistic comparisons among species to determine their commonalities. Additionally, we show that rotifers' jaws, which are perhaps the best-characterized jaws among invertebrates, are still enigmatic with regard to their origins and mechanics. Nevertheless, technologies such as energy dispersive X-ray spectroscopy (EDX) and 3D modeling are being used to characterize their chemical composition and to develop physical models that allow exploration of their mechanical properties, respectively. We predict that these methods can also be used to develop biomimetic and bioinspired constructs based on the full range of the complexity of jaws, and that such constructs also can be developed from other invertebrate taxa. These approaches may also shed light on common developmental and physiological processes that facilitate the evolution of invertebrates' jaws.

Rotifers from selected inland saline waters in the Chihuahuan Desert of México.

BACKGROUND: In spite of considerable efforts over past decades we still know relatively little regarding the biogeography of rotifers of inland waters in México. To help rectify this we undertook an extensive survey of the rotifer fauna of 48 water bodies in the Chihuahuan Desert of México. RESULTS: Of the sites surveyed, 21 had salinities >or= 2000 microS cm-1 and in these we found 57 species of monogonont rotifers and several bdelloids. Species richness in the saline sites varied widely, with a range in species richness of 1 to 27 and a mean (+/- 1SD) = 8.8 (+/- 6.2). Collectively all sites possess relatively high percent single- and doubletons, 33.3 and 21.7%, respectively. Simpson's Asymmetric Index indicated that similarity in rotifer species composition varied widely among a set of 10 sites. These were selected because they were sampled more frequently or represent unusual habitats. These SAI values ranged from 0.00 (complete dissimilarity) to 1.00 (complete similarity). The Jaccard Index varied between 0.00 and 0.35. This observation probably reflects similarities and differences in water chemistry among these sites. Inland saline systems differed in their chemical composition by region. Conductivity was related to hardness and alkalinity. In addition, hardness was positively associated with chloride and sulfate. RDA showed that several species were positively associated with chloride concentration. Other factors that were significantly associated with rotifer species included the presence of macrophytes, nitrate content, oxygen concentration, TDS, latitude and whether the habitat was a large lake or reservoir. CONCLUSION: This study illustrates the diversity of the rotiferan fauna of inland saline systems and the uniqueness among waterbodies. Conservation of these systems is needed to preserve these unique sources of biodiversity that include rotifers and the other endemic species found in association with them.