1,721,022 research outputs found
On some rotifers new for the Italian fauna
No full textFaunistic data concerning rotifer species not previously cited for the Italian fauna are reported. They are all found in the northwestern part of the country and belong to 24 genera, seven of which are new for Italy: Cyrtonia, Didymodactylos, Eosphora, Mikrocodides, Pleuretra, Proalinopsis, and Taphrocampa. For some of these species, data on rearing in laboratory cultures, dimensions, and SEM pictures of trophi or whole animals are given
Redescription of Pleuretra hystrix, an endemic alpine bdelloid rotifer
No full textPleuretra hystrix Bartoš, 1950 is a peculiar bdelloid rotifer unrecorded for more than 50 years since its description.
We found this species in the western Italian Alps and we redescribe it, confirming the validity of this species. New
morphological details are described from scanning electron micrographs. Variability in spines on the trunk is great;
their adaptative significance in bdelloid rotifers is discussed
Bdelloid rotifers from lakes above 1700 m in western Italian Alps, with taxonomic notes on Dissotrocha macrostyla
No full textBenthic and periphytic bdelloid communities from 16 alpine lakes from 1700 to 2850 m in above sea level in Sesia Valley (Piedmont region, North-western Italy), sampled during summer 2001 and 2002, were analyzed. Seventeen species were identified from these species-poor communities, with 1 to 6 species each. Dissotrocha macrostyla and Philodina citrina were the most common species, present in 10 lakes while 9 species were collected from one lake only. New morphological details from S.E.M. pictures of Dissotrocha macrostyla revealed that Dissotrocha macrostyla tuberculata (GOSSE, 1886) is only a seasonal morphotype. Its different appearance is due to the presence of locally distributed microscopic mucous bubbles (diameter 1.41 +/- 0.18 mum) on the trunk surface, produced by the rotifer itself under stressful conditions
Spatial gradients in species diversity of microscopic animals: the case of bdelloid rotifers at high altitude
No full textAim Organisms smaller than 2 mm appear not to follow the spatial patterns in
richness and diversity commonly observed in macroscopic organisms. We
describe spatial patterns in species diversity in a group of microscopic organisms,
bdelloid rotifers, living in moss and lichen patches, in order to test the hypotheses
of no relationship between species richness and composition and spatial
gradients, suggested by previously published patterns in microscopic organisms.
Location Moss and lichen patches as habitats for bdelloids, on high-elevation
peaks at altitudes between 2984 and 4527 m a.s.l. across the Italian, French and
Swiss Alps, with distances among sample sites ranging from 1 m to 420 km, in
comparison with lower-elevation samples at altitudes from 850 to 1810 m a.s.l.
Methods We sampled species assemblages of bdelloid rotifers living in isolated
moss and lichen patches in 47 sites. We described the observed a, b and c
diversities; the heterogeneity of species assemblages; and the estimated number of
species (incidence-based coverage estimator). Patterns in species distribution
were analysed at three different levels: (1) habitat, comparing species richness on
moss and lichen substrates, testing differences in a diversity and heterogeneity
(anova), species composition (analysis of similarities test), and c diversity
(rarefaction curves); (2) altitude, comparing the observed richness with
previously published data from locations well below 2000 m; and (3) distances
between sites, correlating the matrix of Jaccard dissimilarities and the matrix of
geographical distances with a Mantel test.
Results Both species richness and species composition of bdelloid rotifers
differed significantly between mosses and lichens at high elevations, but no
difference was found in the heterogeneity of species assemblages. Alpha diversity
was significantly lower at high-elevation than at low-elevation sites, but the
estimated number of species was not reduced when compared with sites at low
elevations. Geographical distance between sites had no effect on species
composition in either mosses or lichens. The distribution of species was highly
heterogeneous, with a low similarity among assemblages.
Main conclusions As expected, bdelloids appear to occupy habitats selectively.
The altitudinal gradient in species richness for bdelloid rotifers is limited to a
decrease in a diversity only; such a decrease is not caused by a lower number of
species (low c diversity) being able to tolerate harsh conditions, and high-altitude
species are not a subset of species living at lower elevations. The observed values
of a, b and c diversity at high altitudes in the Alps are compatible with the
scenario of a very low number of available propagules because of the low density
of patches of favourable habitat. Our results suggest that the geographical
distribution of animals, and therefore biodiversity patterns, may be strongly
influenced by animal size, as small organisms such as bdelloids appear to show spatial patterns that differ from those known in larger animals. Differences in
body size should be taken into account carefully in future studies of biodiversity
patterns
The importance of being a bdelloid : ecological and evolutionary consequences of dormancy
No full textThe bdelloid rotifers represent an intriguing example of organisms displaying an array of unusual ecological and evolutionary features, yet have managed to remain an extremely successful group for more than 35 million years. Some of these unusual features include: strictly parthenogenetic reproduction, degenerate tetraploidy, horizontal gene transfer, and resistance to desiccation, starvation and ionising radiation. This review emphasises these as well as other ecological and evolutionary features of bdelloids, highlighting the current knowledge regarding the patterns and processes governing these organisms. We suggest a unifying framework, with dormancy representing the bdelloids' key feature. We hypothesise that dormancy, and especially the DNA repair mechanisms activated during dormancy recovery, might be responsible for all the unusual features present in the taxon. We propose further work that needs to be performed to test this hypothesis, and recommend further research areas that will help to unravel this "evolutionary scandal''
Postembryonic development oh hard jaws (trophi) in a species belonging to the Brachionus plicatilis complex (Rotifera, Monogononta) : a morphometric analysis
No full textThe presence of hard jaws (trophi), with species-specific shape and size, is a taxonomic
feature of Rotifera, a group of microscopic metazoans. Since trophi are used to discriminate
among species, it is important to know whether these structures change in taxonomically important
ways during postembryonic development. Using both SEM and optical images, we analyzed more
than 100 individuals of a single clonal lineage of a monogonont rotifer, Brachionus plicatilis, in order
to describe body and trophi development after hatching. Body size, expressed as lorica width and
length, was isometrically related to age of the animals only during preadult stages. Trophi size,
expressed as length of the different parts, was unrelated to either age or body size. Therefore, trophi
elements do not grow after hatching in B. plicatilis. Despite the dimensional invariance with age,
some differences in trophi size among individuals of the same clone were recorded. No difference in
left–right asymmetry of the trophi was shown; the asymmetric elements of the trophi named rami
consistently had the right ramus longer than the left. This constancy is in contrast to the reported
trophi asymmetries in bdelloid rotifers, in which left–right asymmetries are not constant within clonal
lineages. In conclusion, we suggest that also trophi size, constant within the analyzed clone, may
be used as an additional taxonomic feature to help in the discrimination of taxa within the B. plicatilis
complex of cryptic species
Trophi structure in bdelloid rotifers
No full textBdelloids show a rather uniform morphology of jaws (trophi), named ramate. The most recognizable feature is the presence of a series of teeth forming unci plates. The unci are not uniform in size; each plate has 1-10 major median teeth. Using SEM pictures of trophi and data from the literature, we analyzed the number of major unci teeth in relation to trophi size, total number of teeth, and environmental features. Variability in the number of major unci teeth in bdelloids is not related to trophi size or to total number of unci teeth, while total number of unci teeth and trophi size seem to be related to each other: larger trophi in general have more teeth than smaller trophi. Few major teeth are more common in species living in water bodies where they possibly eat unicellular algae, while more major teeth are more common in species living outside water bodies, among mosses and lichens, where they possibly eat bacteria
Do rotifer jaws grow after hatching?
No full textThe hard articulated jaws of some pseudocoelomte metazoans were recently used in reconstructing their phylogenetic relationships, but we still do not know if these structures could change in size and shape during the life of individuals, and experimental data are lacking on their post-embryonic development. Rotifers are one of the groups in which hard articulated jaws, called trophi, are well known, and are widely used taxonomically. Here we report on SEM study of trophi of rotifers of different ages, to determine if the trophi structures change in shape and/or in size during post-embryonic development. We used linear measurements and geometric morphometrics analyses from scanning electron microscopic pictures of trophi of Cupelopagis vorax, Dicranophorus forcipatus, Macrotrachela quadricornifera, Notommata glyphura, Rotaria macrura, R. neptunoida, and R. tardigrada. Results for these species show that trophi do not change after hatching, either in size or in shape. In contrast, data on Asplanchna priodonta reveal trophi growth after hatching
Marine rotifers from the Northern Adriatic Sea, with description of Lecane insulaconae sp. nov. (Rotifera: Monogononta: Lecanidae)
No full textDuring a survey of the marine rotifers of the Northern Adriatic Sea, Italy, we found a total of 20 taxa, including a new species
of Lecane. This novelty, Lecane insulaconae sp. nov., occurred in the interstitial area of sandy sediment in the outlet of the
Isonzo River, at a salinity of 30‰ and is therefore the first exclusively marine representative of this diverse (~200 species)
genus. It is characterized by unique sets of anterolateral projections on the ventral and dorsal lorica. Here, we present the
description of the species, together with scanning electron microscopy pictures of trophi of this and some other species, and
an account of the marine rotifers encountered during the survey
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