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

Influence of experimental set-up and methodology for measurements of metabolic rates and critical swimming speed in Atlantic salmon Salmo salar

In this study, swim‐tunnel respirometry was performed on Atlantic salmon Salmo salar post‐smolts in a 90 l respirometer on individuals and compared with groups or individuals of similar sizes tested in a 1905 l respirometer, to determine if differences between set‐ups and protocols exist. Standard metabolic rate (SMR) derived from the lowest oxygen uptake rate cycles over a 20 h period was statistically similar to SMR derived from back extrapolating to zero swim speed. However, maximum metabolic rate (MMR) estimates varied significantly between swimming at maximum speed, following an exhaustive chase protocol and during confinement stress. Most notably, the mean (±SE) MMR was 511 ± 15 mg O2 kg−1 h−1 in the swim test which was 52% higher compared with 337 ± 9 mg O2 kg−1 in the chase protocol, showing that the latter approach causes a substantial underestimation. Performing group respirometry in the larger swim tunnel provided statistically similar estimates of SMR and MMR as for individual fish tested in the smaller tunnel. While we hypothesised a larger swim section and swimming in groups would improve swimming performance, Ucrit was statistically similar between both set‐ups and statistically similar between swimming alone v. swimming in groups in the larger set‐up, suggesting that this species does not benefit hydrodynamically from swimming in a school in these conditions. Different methods and set‐ups have their own respective limitations and advantages depending on the questions being addressed, the time available, the number of replicates required and if supplementary samplings such as blood or gill tissues are needed. Hence, method choice should be carefully considered when planning experiments and when comparing previous studies.publishedVersio

Operational retrieval of trace gases concentrations from IASI spectra

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