On the ecology of Lecane (Rotifera)

A material consisting of 49 taxa of Lecane (Rotifera), from diverse waters in south and Central Sweden, was analyzed to reveal their relationships to substrate and habitat. Most species did not show any pronounced preference for any substrate, occurring in several diverse substrates, and especially in periphytic environments. Only a few species seemed to specialize in bog substrates. Some taxa were found, sometimes at a high frequency, on an artificial substrate, white cotton, indicating a high degree of mobility.     

Spatial gradients in species diversity of microscopic animals: the case of bdelloid rotifers at high altitude

Aim 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 α, β and γ 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 α diversity and heterogeneity (anova ), species composition (analysis of similarities test), and γ 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 α diversity only; such a decrease is not caused by a lower number of species (low γ 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 α, β and γ 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.     

Extreme levels of hidden diversity in microscopic animals (Rotifera) revealed by DNA taxonomy

Knowledge and estimates of species richness at all scales are biased both by our understanding of the evolutionary processes shaping diversity and by the methods used to delineate the basic units of diversity. DNA taxonomy shows that diversity may be underestimated by traditional taxonomy, especially for microscopic animals. The effects of such hidden diversity are usually overlooked in ecological studies. Here, we estimate hidden diversity in bdelloid rotifers, a group of microscopic animals. We analyse cryptic diversity using a coalescent approach to infer taxonomical units from phylogenetic trees. Cryptic diversity was measured for eight traditional species of bdelloid rotifers and the results compared to that of the monogonont rotifer Brachionus plicatilis species complex, which is well studied and for which cross-mating experiments have been performed to explicitly define some of the species boundaries. A taxonomic inflation of up to 34 potential cryptic taxa was found in bdelloids. Cryptic taxa within each traditional species may be spatially isolated, but do not have narrower ecological niches. The species deemed as generalists exhibit the highest cryptic diversity. Cryptic diversity based on molecular characterization is commonly found in animals; nevertheless, the amount of cryptic diversity in bdelloids is much higher than in other groups analysed so far, maybe because of their peculiar parthenogenetic reproduction, other than microscopic size. We discuss this hypothesis in the light of the available empirical evidence from other groups of microscopic invertebrates, such as tardigrades and mites, which share size, habitat heterogeneity, potential for dispersal, and/or parthenogenetic reproduction.     

Microfauna associated with algal mats in melt ponds of the Ross Ice Shelf

Summary The microfauna of benthic algal mats in eight ponds of diverse chemistry on the Ross Ice Shelf was examined. Tardigrades, nematodes and rotifers were successfully extracted from algal material by a modified Baermann funnel technique, which was robust enough to use under field conditions. Seven species of rotifer (of which 6 were bdelloids) and one species of nematode and tardigrade were found, all of which are cosmopolitan to Antarctic lentic ecosystems. Philodina sp. was the only invertebrate to occur in all ponds sampled. Rotifers were the most abundant invertebrates with average densities in all ponds of 4.26×10⁵ individuals/m², whereas nematodes were least abundant with densities of 4.96×10⁴ individuals/m². Total invertebrate densities and densities of individual taxa were significantly different in each of the 8 ponds, and of those measured environmental parameters were most strongly associated with conductivity. Cores taken from four ponds 2 cm into underlying substratum revealed that most animals live within the algal mats, with underlying sediment supporting a minimal population.     

Surviving starvation: Changes accompanying starvation tolerance in a bdelloid rotifer

Bdelloid rotifers survive desiccation and starvation by halting activity and entering a kind of dormancy. To understand the mechanisms of survival in the absence of food source, we studied the anatomical and ultrastructural changes occurring in a bdelloid species, Macrotrachela quadricornifera Milne 1886, after starvation for different periods. The starved rotifers present a progressive reduction of body size accompanied with a consistent reduction of the volume of the stomach syncytium, where lipid inclusions and digestive vacuoles tend to fade with prolonged starvation. Similar reduction occurs in the vitellarium gland, in which yolk granules progressively decrease in number and size. The changes observed in the syncytia of the stomach and the vitellarium suggest that during starvation M. quadricornifera uses resources diverted from the stomach syncytium first and from the vitellarium syncytium later, resources that are normally allocated to reproduction. The fine structure of starved bdelloids is compared with that of anhydrobiotic bdelloids, revealing that survival during either forms of dormancy is sustained by different physiological mechanisms. J. Morphol., 2011. © 2011 Wiley Periodicals, Inc.     

On the reality and recognisability of asexual organisms: morphological analysis of the masticatory apparatus of bdelloid rotifers

Species concepts and definitions have been a long-standing debate in evolutionary biology since before Darwin, and almost all proposed solutions are based upon grouping and clustering, with species conceived as somehow biological distinct entities, originated and maintained mainly by reproductive isolation. Lacking reproductive exchange, asexual organisms such as bdelloid rotifers, the best-supported clade of so-called 'ancient asexuals', pose an interesting challenge to debates over the reality of species. However, few data are available on bdelloid rotifers. The only evidence has been that bdelloid species have been more consistently recognised than in their sister sexual group, the monogonont rotifers, across successive taxonomic treatments, but this is confounded by the much lesser degree of taxonomic interest in bdelloids. We applied geometric morphometrics analyses on shape and size of hard masticatory pieces, named trophi, of 1420 bdelloids, belonging to 48 populations of eight traditional species, to test the hypothesis of recognisability of bdelloids. Our morphological analysis confirms that traditional bdelloid species are separated distinct entities, possessing trophi morphologies divided by gaps between taxa, similar to patterns of morphological features in sexually reproducing organisms. In common with most microscopic understudied organisms, bdelloid rotifers harbour much previously undescribed diversity: we found significant differences in trophi morphology within traditional species, revealing the existence of cryptic taxa, similar to those also found in facultatively sexual monogonont rotifers. We confirm that recognisability in bdelloids is not qualitatively different from other small understudied animals such as monogononts, and that sexual versus asexual reproduction does not lead to differences in morphological diversity patterns, as previously suggested based on interpretation of taxonomic revisions.     

Rotifers of the Kalahari Gemsbok National Park,South Africa

The Kalahari Gemsbok National Park in the Northern Cape Province, South Africa, is bounded by two dry river beds in which 39 artificial water sources have been provided for the use of the wild animals. The water in these sources varies from fresh to highly saline and an opportunity is thus provided to determine, not only which rotifer species are able to colonise such sources, but what their salinity tolerances are. The rotifer fauna, studied in summer and winter, is dominated by mixed populations of Brachionus calyciflorus, B. plicatilis and Hexarthra jenkinae, with only a few other monogononts and bdelloids. The most striking feature of the rotifer fauna in these troughs is the very low species diversity encountered.     

On the ecology of Cephalodella

A material consisting of 66 species of Cephalodella (Rotifera), from diverse waters in south and central Sweden, was analyzed to reveal their possible relationships to substrate and habitat. Most species preferred periphytic environments. Most species have a broad ecological range, only a few being bog specialists. An artificial substrate, white cotton, was colonized by several species, even some without eyes.     

Evidence of weak habitat specialisation in microscopic animals

Macroecology and biogeography of microscopic organisms (any living organism smaller than 2 mm) are quickly developing into fruitful research areas. Microscopic organisms also offer the potential for testing predictions and models derived from observations on larger organisms due to the feasibility of performing lab and mesocosm experiments. However, more empirical knowledge on the similarities and differences between micro- and macro-organisms is needed to ascertain how much of the results obtained from the former can be generalised to the latter. One potential misconception, based mostly on anedoctal evidence rather than explicit tests, is that microscopic organisms may have wider ecological tolerance and a lower degree of habitat specialisation than large organisms. Here we explicitly test this hypothesis within the framework of metacommunity theory, by studying host specificify in the assemblages of bdelloid rotifers (animals about 350 μm in body length) living in different species of lichens in Sweden. Using several regression-based and ANOVA analyses and controlling for both spatial structure and the kind of substrate the lichen grow over (bark vs rock), we found evidence of significant but weak species-specific associations between bdelloids and lichens, a wide overlap in species composition between lichens, and wide ecological tolerance for most bdelloid species. This confirms that microscopic organisms such as bdelloids have a lower degree of habitat specialisation than larger organisms, although this happens in a complex scenario of ecological processes, where source-sink dynamics and geographic distances seem to have no effect on species composition at the analysed scale.     

On the ecology of Trichocercidae (Rotifera)

A material consisting of 46 trichocercid rotifers from diverse waters in south and central Sweden was analyzed to reveal their relationships to their substrate. Most species were found in a wide variety of periphytic environments, but a few seemed to be specialized on bogs or psammon, respectively. Several trichocercids are generally regarded as plankters, but some of them obviously invade the open water only on certain occasions. A few species of Trichocerca are registered as indicators of eutrophy, but in some cases only a planktic occurrence may be regarded as indicating. On the other hand, hypertrophic environments are generally avoided. Trichocerca similis prefers polyhumic environments, T. uncinata oligotrophic and running-water conditions. The occurrence is often best explained by studying the food choice.     

Saprophagous insect larvae,Drosophila melanogaster,profit from increased species richness in beneficial microbes

Female fruit flies, Drosophila melanogaster, lay their eggs on decaying plant material. Foraging fly larvae strongly depend on the availability of dietary microbes, such as yeasts, to reach the adult stage. In contrast, strong interference competition with filamentous fungi can cause high mortality among Drosophila larvae. Given that many insects are known for employing beneficial microbes to combat antagonistic ones, we hypothesized that fly larvae engaged in competition with the noxious mould Aspergillus nidulans benefit from the presence of dietary yeast species, especially when they are associated with increasingly species rich yeast communities (ranging from one to six yeast species per community). On a nutrient‐limited fruit substrate infested with A. nidulans, both larval survival and development time were positively affected by more diverse yeast communities. On a mould‐free fruit substrate, merely larval development but not survival was found to be affected by increasing species richness of dietary yeasts. Not only yeast diversity had an effect on D. melanogaster life‐history traits, but also the identity of the yeast combinations. These findings demonstrate the importance of the structure and diversity of microbial communities in mutualistic animal–microbe interactions.     

To bde or not to bde: Sex and the bdelloid rotifer

Most species eventually end up having sex, but not the bdelloids, and in pondering what lies beyond what we can see in evolution, there's the rub.     

Natural taxonomic categories of angiosperms obey Benford's law,but artificial ones do not

Benford's phenomenological law gives the expected frequencies of the first significant digit (i.e., the leftmost non-zero digit) of any given series of numbers. According to this law, the frequency of 1 is higher than that of 2; this in turn appears more often than 3, and so on decreasing until 9. Similarly, Benford's law can also be applied to the first two significant digits (i.e., from 10 to 99), and so on. We applied Benford's law to sets of taxonomic data sets consisting of the number of taxa included in taxa of higher rank. We chose the angiosperms (Magnoliophyta) as a model case, because they are very diverse, are monophyletic, and a consensus on taxonomy of orders and families has been achieved (classification APG III), and we used as sets of data the number of species, genera, families, and orders. Only the number of species per family and per order are Benford's sets, but the remaining data sets do not obey Benford. Furthermore, in the case of the analysis of the first two significant digits of species per genus, the deviation from Benford was very large, but they fit to a power law. Given that the conformity to Benford's law is fulfilled for ‘natural' taxonomic categories of angiosperms (i.e., species and family), but not for those with more artificiality (genus), we speculate, ‘the more natural, the more Benford'.     

A carnivorous bdelloid rotifer, Abrochtha carnivora n.sp.

Abstract. Here we describe a new bdelloid rotifer, Abrochtha carnivora n.sp., that preys on other bdelloids and monogonont rotifers. This is the first report of predatory behavior in bdelloids. Despite this extraordinary behavior, A. carnivora displays no major structural deviation from the standard body plan for members of the bdelloid family Philodinavidae: body with head (with ciliated corona), trunk, and foot, mastax with ramate trophi. The finding of such a carnivorous species, unique for the class, appears to contradict the common assumption that the wholly parthenogenetic bdelloids are evolutionary dead-ends.     

Patterns of diversity in microscopic animals: are they comparable to those in protists or in larger animals?

Aim General patterns of biodiversity, such as latitudinal gradients and species‐area relationships, are found consistently in a wide range of organisms, but recent results for protist diversity suggest that organisms shorter than 2 mm do not display such patterns. We tested this prediction in bdelloid rotifers, pluricellular metazoans smaller than 2 mm, but with size and ecology comparable to protists. Location A single valley in northern Italy was surveyed in detail and compared to all available faunistic data on bdelloids worldwide. Methods We analysed 171 local assemblages of bdelloid rotifers living in 5 systems of dry mosses and submerged mosses in running water and in lakes. We compared patterns of alpha, beta, and gamma diversity, and nestedness of metacommunities, with those known from protists and larger organisms. Results Bdelloid rotifers showed low local species richness (alpha diversity), with strong habitat selection, as observed in larger organisms. The number of species differed among systems, with a higher number of species in dry than in aquatic mosses. There was no hierarchical structure or exclusion of species in the metacommunity pattern within each system. Local diversity for the entire valley was surprisingly high compared with worldwide bdelloid diversity, similar to observed patterns in protists. Main Conclusions Bdelloid rotifers have some of the peculiarities of protist biodiversity, although at slightly different spatial scales, thus confirming the idea of a major change in biodiversity patterns among organisms shorter than 2 mm. However, bdelloids show stronger habitat selection than protists. We suggest two possible explanations for the observed patterns: (1) dispersal is very rare, and not all bdelloid clones are arriving everywhere; and (2) dispersal is effective in displacing propagules, but environmental heterogeneity is very high and prevents many species from colonizing a given patch of moss.     

The effect of partial and total drought on the macroinvertebrate communities of three small Danish streams

Three cases of partial or total drought were studied. A two weeks' stop of water flow with reduced water level and stagnant water was survived by most stream species. Only the population of Baetis rhodani Pict. was almost eliminated. An unprecedented drought of 2-3 months reduced numbers of stream species. The differential effects are discussed in relationship to the behaviour, life cycle and physiology of the individual species. After the drought many invaders were found, but most disappeared rapidly. Only Asellus aquaticus L. maintained a population in the stream. In an intermittent stream with 3–4 months' drought no changes were observed, and many species were the same as those which survived in the second stream. It is concluded that the consequences of an increasing frequency of drought, for example due to increasing ground water use, will depend on the species normally present and on the season and duration of the drought.     

HEAVY METAL ACCUMULATION AND THE NATURE OF EDAPHIC ENDEMISM IN THE GENUS CALOCHORTUS (LILIACEAE)

Bulb and leaf tissues from five species in the genus Calochortus and the soils from collection sites were analyzed for cation and trace element concentrations. All five species, only three of which are considered ultramafic endemics, possessed high concentrations of nickel and copper in both the bulbs and leaves, but not at levels high enough (> 1% dry wt) to be considered hyperaccumulators. Only moderate to trace amounts of cobalt and chromium were detected in both plant tissues. Calcium-magnesium ratios, typically low in ultramafic soils and plants, were low in bulb tissue, but two to 10 times higher in leaf tissue. The ability to tolerate excessively high levels of nickel and other heavy metals may be a physiological exaptation of the genus Calochortus and not necessarily an evolutionary response by several species to life on an ultramafic substrate. The nature of “serpentine” endemism is discussed in the context of heavy metal accumulation by various plant species.     

Beech versus spruce deadwood as forest microhabitat: does it make any difference to bryophytes?

The presence data of 153 bryophyte species, recorded on beech (BDW) and spruce (SDW) deadwood in the managed forests within a montane watershed, were analysed by controlling for different plot size, substrate pH and elevation. Only three pleurocarpous species, which were probably remnant epiphytes from live wood, showed relative specificity for BDW, but none to SDW. The few species displaying preference for BDW or SDW were generally true epixylic, mosses and hepatics, respectively. The chances of occurrence of epiphytic (early successional) and epixylic (mid-late successional) taxa on either deadwood species increased and respectively, decreased with the substrate pH. There was no consistent relationship between bryophyte preference to BDW/SDW and elevation. Neither total nor threatened species richness was related to deadwood species identity. However, at 100 cm² resolution and within certain extension range, the cumulative number of bryophyte species was significantly higher on BDW than on SDW, despite no significant difference in species pool size. Threatened species richness increased monotonically towards lower elevations, suggesting that valley bottoms might act as refugia with high air humidity. The number of threatened species and in particular, the presence of Lophozia ascendens, were good predictors of total bryophyte richness regardless of deadwood species identity.     

Influence of substrate preference and complexity on co-existence of two non-native gammarideans (Crustacea: Amphipoda)

Substrate choice, swimming activity and risk to predation by burbot (Lota lota) of the well established Gammarus roeselii and the invader Dikerogammarus villosus were studied in mixed and single-species aquarium experiments. We used stones, gravel and aquatic weeds (Elodea, Chara) as substrates. We hypothesized that both species have different substrate preferences and that substrate affects the predation risk. We also assumed that presence of D. villosus influences substrate preference and predation risk of G. roeselii since the invader is known to affect the behavior of other gammarids. Adults of D. villosus in single species experiments and juveniles in mixed and single species experiments were evenly distributed over the different substrates but adults in mixed species experiments were more likely to prefer stone substrate. In contrast, adults and juveniles of G. roeselii clearly preferred aquatic weeds independent of the presence/absence of the invader. Both species preferred substrates with fissured surface over substrates with smooth surface. Gammarus roeselii was observed swimming more often than D. villosus in the open water but its swimming activity was lower when its preferred substrate was present compared with its swimming activity if non-preferred substrates were present. Predation rate of burbot on D. villosus was comparatively low and independent of the substrate. Burbot consumed many more G. roeselii than D. villosus, both in mixed and single species experiments. But when the preferred substrate of G. roeselii (weeds) was used in the experiments, predation rate of burbot on G. roeselii was somewhat lower than that when non-preferred substrates were present. The results of the experiments support our hypothesis that the gammarids studied here have different substrate preferences and that presence of the preferred substrate can affect predation risk. However, there is no evidence that presence of D. villosus affected substrate choice or predation risk in G. roeselii. We consider that differences in use of spatial niches permit co-existence of G. roeselii and D. villosus in the wild when substrates are diverse. The fact that G. roeselii than D. villosus is more often observed swimming in the open water may explain its higher risk of being captured by fish.     

A comparative study of diet in three sympatric populations of<Emphasis Type="Italic"> Patagonotothen</Emphasis> species (Pisces: Nototheniidae)

The diet of three Patagonotothen species was investigated from the bycatch of near-bottom trawls for squid on the southern Falkland Island shelf. Patagonotothen ramsayi had a moderately diverse diet that was mostly zooplankton, especially amphipods, but included benthos and discards from the fishery, especially squid. P. guntheri also had a moderately diverse zooplankton diet, especially copepods, and benthos and squid damaged by the fishery. The diet of P. tessellata was the most diverse and was mainly benthos, including damaged scallops, with some euphausiids and amphipods. Feeding niche overlap of fish between 10 and 20 cm TL for the three species was between 5.8 and 9.2% for each pair of species, indicating relatively little overlap even though all species scavenged on organisms made available by the fishery. Thus the diet of these three Patagonotothen species indicates substantial feeding niche separation, and that the three species are moderately specialised feeders.