Differences in time until dispersal between cryptic species of a marine nematode species complex

Co-occurrence of closely related species may be achieved in environments with fluctuating dynamics, where competitively inferior species can avoid competition through dispersal. Here we present an experiment in which we compared active dispersal abilities (time until first dispersal, number and gender of dispersive adults, and nematode densities at time of dispersal) in Litoditis marina, a common bacterivorous nematode species complex comprising four often co-occurring cryptic species, Pm I, II, III, and IV, as a function of salinity and food distribution. The experiment was conducted in microcosms consisting of an inoculation plate, connection tube, and dispersal plate. Results show species-specific dispersal abilities with Pm I dispersing almost one week later than Pm III. The number of dispersive adults at time of first dispersal was species-specific, with one dispersive female in Pm I and Pm III and a higher, gender-balanced, number in Pm II and Pm IV. Food distribution affected dispersal: in absence of food in the inoculation plate, all species dispersed after ca four days. When food was available Pm I dispersed later, and at the same time and densities irrespective of food conditions in the dispersal plate (food vs no food), suggesting density-dependent dispersal. Pm III dispersed faster and at a lower population density. Salinity affected dispersal, with slower dispersal at higher salinity. These results suggest that active dispersal in Litoditis marina is common, density-dependent, and with species, gender- and environment-specific dispersal abilities. These differences can lead to differential responses under suboptimal conditions and may help to explain temporary coexistence at local scales

To stay or go: differential dispersal rates in cryptic species of a marine nematode

Behind the morphological similarity of many species, a hidden genetic diversity can be found. This cryptic diversity has been well documented in the marine nematode Rhabditis (Pellioditis) marina, a common bactivore associated with decomposing macro-algae in the littoral zone of coastal and estuarine environments. Four cryptic species of R. marina (Pm I, Pm II, Pm III and Pm IV) co-occur along the south-western coast and estuaries of The Netherlands. This coexistence challenges traditional competition theory, which states that competition will be most severe between closely related species. A previous study showed that competition between the four cryptic species occurred, but interspecific interactions were affected by environmental conditions such as salinity. One of the most important mechanisms to react to competition is dispersal. Most organisms have at least one stage in which dispersal occurs over a specific spatial scale. Meiobenthic species, however, lack any pelagic stage. But, recent research shows more and more evidence that meiofauna is also able to actively disperse with lateral sinusoidal movements in the interstitial spaces as one of the most common modes of dispersal of nematodes over short distances. Dispersal is a process triggered partially by the internal conditions of organisms and partially by environmental conditions. In the current experiment, species-specific differences in active dispersal rates and the effects of salinity and food distribution on dispersal behaviour were tested in four cryptic species of R. marina (Pm I, Pm II, Pm III and Pm IV), The results of the experiment showed that dispersal is a species-specific behaviour with Pm III being the most rapid disperser (first dispersal event occurred after an average of 3 days), and Pm I the slowest disperser (average of 10 days). An effect of food distribution on the dispersal rates of all cryptic species was found with the most rapid dispersal if no food was present at the start situation. Salinity also had an effect with a higher dispersal rate at lower salinity for all the species. Moreover, the number of dispersive organisms differed between the species, with only one female disperser in Pm I and Pm III and a mix of female and male dispersers for Pm II and Pm IV at the first dispersal event. This species-specific dispersal behaviour and the influence of external conditions on dispersal can influence the reaction on competition. In a future experiment the effect of competition on dispersal will be studied by using competition cultures, where all four cryptic species can influence each other, but the organisms have the chance to disperse away. These results are important to better understand the processes behind the coexistence of cryptic species

Throughput of ADSL modems

This paper considers the throughput of ADSL (Asymmetric Digital Subscriber Line) modems, used for high-speed data transmission over relatively unreliable connections, e.g. copper telephone wires. The modem technique uses an error correcting code and interleaving. The settings include a grouping factor $S$ which affects the amount of data per code word, the number $R$ of redundant bytes per code word and the interleave depth $D$. The influence of these parameters on both the effective data transmission rate and the resulting error rate in the received signal are determined for two error situations: random errors and bursts of errors. An approximate analysis for the random error case of the throughput of a TCP (Transport Control Protocol) connection using an ADSL modem shows that maximum throughput is obtained for the highest values of $S$ and $R$

Black Dialect in Children\u27s Books

Black non-Standard English is different in grammar (syntax) from Standard English. The advent of the 60\u27s produced authors who explored the full possibilities of language to deal with their themes. The increased use of dialect by black authors, particularly children\u27s authors, was a sign that the nature of the black experience as they wanted to convey it did not have to rely on traditional forms, and literary devices; that they could treat familiar, realistic ideas and situations using a familiar dialect and relate that idea more effectively

Coexisting cryptic species of the Litoditis marina complex (Nematoda) show differential resource use and have distinct microbiomes with high intraspecific variability

Differences in resource use or in tolerances to abiotic conditions are often invoked as potential mechanisms underlying the sympatric distribution of cryptic species. Additionally, the microbiome can provide physiological adaptations of the host to environmental conditions. We determined the intra-and interspecific variability of the microbiomes of three cryptic nematode species of the Litoditis marina species complex that co-occur, but show differences in abiotic tolerances. Roche 454 pyrosequencing of the microbial 16S rRNA gene revealed distinct bacterial communities characterized by a substantial diversity (85-513 OTUs) and many rare OTUs. The core microbiome of each species contained only very few OTUs (2-6), and four OTUs were identified as potentially generating tolerance to abiotic conditions. A controlled experiment in which nematodes from two cryptic species (Pm1 and Pm3) were fed with either an E. coli suspension or a bacterial mix was performed, and the 16S rRNA gene was sequenced using the MiSeq technology. OTU richness was 10-fold higher compared to the 454 data set and ranged between 1118 and 7864. This experiment confirmed the existence of species-specific microbiomes, a core microbiome with few OTUs, and high interindividual variability. The offered food source affected the bacterial community and illustrated different feeding behaviour between the cryptic species, with Pm3 exhibiting a higher degree of selective feeding than Pm1. Morphologically similar species belonging to the same feeding guild (bacterivores) can thus have substantial differences in their associated microbiomes and feeding strategy, which in turn may have important ramifications for biodiversity-ecosystem functioning relationships

Chytrid epidemics may increase genetic diversity of a diatom spring-bloom

Contrary to expectation, populations of clonal organisms are often genetically highly diverse. In phytoplankton, this diversity is maintained throughout periods of high population growth (that is, blooms), even though competitive exclusion among genotypes should hypothetically lead to the dominance of a few superior genotypes. Genotype-specific parasitism may be one mechanism that helps maintain such high-genotypic diversity of clonal organisms. Here, we present a comparison of population genetic similarity by estimating the beta-dispersion among genotypes of early and peak bloom populations of the diatom Asterionella formosa for three spring-blooms under high or low parasite pressure. The Asterionella population showed greater beta-dispersion at peak bloom than early bloom in the 2 years with high parasite pressure, whereas the within group dispersion did not change under low parasite pressure. Our findings support that high prevalence parasitism can promote genetic diversification of natural populations of clonal hosts

Strong differences in the clonal variation of two Daphnia species from mountain lakes affected by overwintering strategy

<p>Abstract</p> <p>Background</p> <p>The population structure of cyclical parthenogens such as water fleas is strongly influenced by the frequency of alternations between sexual and asexual (parthenogenetic) reproduction, which may differ among populations and species. We studied genetic variation within six populations of two closely related species of water fleas of the genus <it>Daphnia </it>(Crustacea, Cladocera). <it>D. galeata </it>and <it>D. longispina </it>both occur in lakes in the Tatra Mountains (Central Europe), but their populations show distinct life history strategies in that region. In three studied lakes inhabited by <it>D. galeata</it>, daphnids overwinter under the ice as adult females. In contrast, in lakes inhabited by <it>D. longispina</it>, populations apparently disappear from the water column and overwinter as dormant eggs in lake sediments. We investigated to what extent these different strategies lead to differences in the clonal composition of late summer populations.</p> <p>Results</p> <p>Analysis of genetic variation at nine microsatellite loci revealed that clonal richness (expressed as the proportion of different multilocus genotypes, MLGs, in the whole analysed sample) consistently differed between the two studied species. In the three <it>D. longispina </it>populations, very high clonal richness was found (MLG/N ranging from 0.97 to 1.00), whereas in <it>D. galeata </it>it was much lower (0.05 to 0.50). The dominant MLGs in all <it>D. galeata </it>populations were heterozygous at five or more loci, suggesting that such individuals all represented the same clonal lineages rather than insufficiently resolved groups of different clones.</p> <p>Conclusions</p> <p>The low clonal diversities and significant deviations from Hardy-Weinberg equilibrium in <it>D. galeata </it>populations were likely a consequence of strong clonal erosion over extended periods of time (several years or even decades) and the limited influence of sexual reproduction. Our data reveal that populations of closely related <it>Daphnia </it>species living in relatively similar habitats (permanent, oligotrophic mountain lakes) within the same region may show strikingly different genetic structures, which most likely depend on their reproductive strategy during unfavourable periods. We assume that similar impacts of life history on population structures are also relevant for other cyclical parthenogen groups. In extreme cases, prolonged clonal erosion may result in the dominance of a single clone within a population, which might limit its microevolutionary potential if selection pressures suddenly change.</p