Assembly of zooplankton communities in newly created ponds

1. The creation or severe disturbance of habitat patches is generally followed by a phase of community (re)assembly. After such an event, the trajectory of community assembly in habitat patches may be highly variable because of stochasticity during the dispersal and colonization process. Conversely, assembly patterns may also be deterministic if communities are shaped by prevalent environmental conditions in the habitat patches (species sorting), or by systematic differences in the dispersal capacities of species. 2. In this study, we investigated the pattern of community assembly of zooplankton species in 25 newly created ponds at 13 different sites in Flanders (Belgium). Over a period of three consecutive years, we assessed at what rate and with what frequency species of the regional species pool colonized the newly created ponds. We also studied the development of community structure over time and tested whether the dynamics were consistent across different ponds at the different locations. In addition, we characterized the dynamics of metacommunity features, such as alpha, beta and gamma diversity in clusters of ponds. 3. Even within the first year after their creation, the new ponds were rapidly colonized by a small subset of species from the regional species pool (Daphnia obtusa, Chydorus sphaericus and Simocephalus vetulus). These species dominated the cladoceran assemblages during the subsequent years. Other species in the regional species pools were only sporadically able to colonize ponds. 4. During the entire study period, we observed no significant shifts in species lists or in the occurrences of species among years. The low incidence of the majority of species may be the result of dispersal limitation or the failure of immigrants to establish due to priority effects exerted by the first colonizers. There was, nevertheless, a consistent change in the relative abundance of species, which was most probably mediated by differences in the hatching time among species influencing species composition in the first year. 5. In contrast to expectations, we observed no increase in average alpha diversity (local species richness) and gamma diversity (total richness of entire pond clusters) during the course of the study period. Beta diversity was relatively low from the beginning and remained constant throughout the study period. These deterministic patterns can mainly be attributed to the dominance of the three first colonizing species and the low success rate of other species in colonizing the ponds.     

Conservation of the introgressed European water frog complex using molecular tools

In Belgium, the Pelophylax esculentus complex has recently been subjected to multiple introductions of non-native water frogs, increasing the occurrence of hybridisation events. In the present study, we tested the reliability of morphometric and recently developed microsatellite tools to identify introgression and to determine the origin of exotic Belgian water frogs. By analysing 150 individuals of each taxon of the P. esculentus complex and an additional 60 specimens of the introduced P. cf. bedriagae , we show that neither of the currently available tools appears to have sufficient power to reliably distinguish all Belgian water frog species. We therefore aimed at increasing the discriminatory power of a microsatellite identification tool by developing a new marker panel with additional microsatellite loci. By adding only two new microsatellite loci (RlCA5 and RlCA1b20), all taxa of the P. esculentus complex could be distinguished from each other with high confidence. Three more loci (Res3, Res5 and Res17) provided a powerful discrimination of the exotic species.     

Morphometric correlates of karyotype and host plant in genus Euceraphis (Hemiptera: Aphididae)

Abstract Samples of birch- and alder-feeding aphids of genus Euceraphis were measured and analysed using multiple discriminant analysis (canonical variates) to find out if morphological variation correlated with previously reported differences of karyotype and host association. The dataset comprised groups of specimens defined solely by locality and collection date. Mean scores on the first two canonical variates clustered the samples fully in accordance with their karyotypes and host plants, confirming the existence of a number of morphologically similar but distinct host-specific taxa within the E. betulae group. Three new species are described: Euceraphis borealis Blackman, sp.n. on Betula glandulosa and B. nana , Euceraphis papyrifericola Blackman, sp.n. on B. papyrifera , and Euceraphis quednaui Blackman, sp.n. on B. occidentalis . A key is provided to alate viviparae of the genus.     

Sensitivity of Laminariales zoospores from Helgoland (North Sea) to ultraviolet and photosynthetically active radiation: implications for depth distribution and seasonal reproduction

Depth distribution of kelp species in Helgoland (North Sea) is characterized by occurrence of Laminaria digitata in the upper sublittoral, whereas L. saccharina and L. hyperborea dominate the mid and lower sublittoral region. Laminaria digitata is fertile in summer whereas both other species are fertile in autumn/winter. To determine the light sensitivity of the propagules, zoospores of L. digitata, L. saccharina and L. hyperborea were exposed in the laboratory to different exposure times of photosynthetically active radiation (PAR; 400–700 nm), PAR + UVA radiation (UVAR; 320–400 nm) and PAR + UVAR + UVB radiation (UVBR; 280–320 nm). Optimum quantum yield of PSII and DNA damage were measured after exposure. Subsequently, recovery of photosynthetic efficiency and DNA damage repair, as well as germination rate were measured after 2 and 3 d cultivation in dim white light. Photosynthetic efficiency of all species was photoinhibited already at 20 µmol photons m⁻² s⁻¹ PAR, whereas UV radiation (UVR) had a significant additional effect on photoinhibition. Recovery of the PSII function was observed in all species but not in spores exposed to irradiation longer than 4 h of PAR + UVA + UVB and 8 h of PAR + UVA. The amount of UVB-induced DNA damage measured as cyclobutane–pyrimidine dimers (CPDs) increased with exposure time and highest damage was detected in the spores of lower subtidal L. hyperborea relative to the other two species. Significant removal of CPDs indicating repair of DNA damage was observed in all species after 2 d in low white light especially in the spores of upper subtidal L. digitata. Therefore, efficient DNA damage repair and recovery of PSII damage contributed to the germination success but not in spores exposed to 16 h of UVBR. UV absorption of zoospore suspension in L. digitata is based both on the absorption by the zoospores itself as well as by exudates in the medium. In contrast, the absorption of the zoospore suspension in L. saccharina and L. hyperborea is based predominantly on the absorption by the exudates in the medium. This study indicates that UVR sensitivity of zoospores is related to the seasonal zoospore production as well as the vertical distribution pattern of the large sporophytes.     

Aminoacylation and conformational properties of yeast mitochondrial tRNA mutants with respiratory deficiency

We report the identification and characterization of eight yeast mitochondrial tRNA mutants, located in mitochondrial tRNA(Gln), tRNA(Arg2), tRNA(Ile), tRNA(His), and tRNA(Cys), the respiratory phenotypes of which exhibit various degrees of deficiency. The mutations consist in single-base substitutions, insertions, or deletions, and are distributed all over the tRNA sequence and structure. To identify the features responsible for the defective phenotypes, we analyzed the effect of the different mutations on the electrophoretic mobility and efficiency of acylation of the mutated tRNAs in comparison with the respective wild-type molecules. Five of the studied mutations determine both conformational changes and defective acylation, while two have neither or limited effect. However, variations in structure and acylation are not necessarily correlated; the remaining mutation affects the tRNA conformation, but not its acylation properties. Analysis of tRNA structures and of mitochondrial and cytoplasmic yeast tRNA sequences allowed us to propose explanations for the observed defects, which can be ascribed to either the loss of identity nucleotides or, more often, of specific secondary and/or tertiary interactions that are largely conserved in native mitochondrial and cytoplasmic tRNAs.