Changes in wet meadow vegetation after 20 years of different management in a field experiment (North-West Germany)

Conservation and restoration of semi-natural wet grasslands often suffer from poor knowledge on successional pathways of respective habitats under different mowing treatments to derive profound management concepts. In this study, we present the results of a 20-year experiment in six semi-natural wet grassland sites in NW Germany including mowing with and without fertilizer addition and fallow. Succession was recorded by permanent plots. The studied wet grassland communities responded quite similar under equal management. Fallow resulted in the most significant changes in floristic and functional composition facilitating highly competitive rushes and tall forbs. The changes were more pronounced the more the experimental management treatment differed from the former use. For all mowing treatments without fertilizer application, we still observed directed changes in the floristic composition even after 20 years. In particular mowing twice led to a shift in floristic composition towards stress-tolerant plants with low nutrient demands, which was paralleled by decreasing productivity and strongly diminishing Ellenberg nutrient values. Our results documented that restoration of low-yielding target communities by regular mowing is possible – even in an area with high atmospheric nitrogen inputs. However, our results also show that succession did not come to an end even after 20 years, most obviously due to the continuous but very slow immigration and spread of new species.     

Greenberg dysplasia: first reported case with additional non-skeletal malformations and without consanguinity

The original article to which this Erratum refers was published in Prenatal Diagnosis 20(12) 2000, 1008–1011.     

Agriotes proximus and A. lineatus (Coleoptera: Elateridae): a comparative study on the pheromone composition and cytochrome c oxidase subunit I gene sequence

The presence of geranyl octanoate, previously found in pheromone gland extracts of Agriotes lineatus females, was also demonstrated in gland extracts of A. proximus females. Similar to A. lineatus, geranyl butanoate was present only in trace amounts in A. proximus female gland extracts. In air entrainment samples of female A. lineatus and A. proximus beetles, the relative ratio of geranyl butanoate and geranyl octanoate was higher than that in gland extracts. In addition, comparison of a segment of the mitochondrial cytochrome c oxidase subunit I gene of feral specimens of A. lineatus and A. proximus showed >99% similarity. Both pheromone profile and nucleotide sequence analysis delineate close relationship between the investigated taxa and postulate taxonomic revision. Further studies on sympatric populations of A. lineatus and A. proximus are underway to investigate and better understand possible processes of species diversification.     

Ultrastructure of pedal muscle as a function of temperature in nacellid limpets

Temperature and mitochondrial plasticity are well studied in fishes, but little is known about this relationship in invertebrates. The effects of habitat temperature on mitochondrial ultrastructure were examined in three con-familial limpets from the Antarctic (Nacella concinna), New Zealand (Cellana ornata), and Singapore (Cellana radiata). The effects of seasonal changes in temperature were also examined in winter and summer C. ornata. Stereological methods showed that limpet pedal myocytes were 1–2 orders of magnitude smaller in diameter (≈3.5 μm) than in vertebrates, and that the diameter did not vary as a function of temperature. Mitochondrial volume density (Vv_(mt,f)) was approximately 2–4 times higher in N. concinna (0.024) than in the other species (0.01 and 0.006), which were not significantly different from each other. Mitochondrial cristae surface density (Sv_(im,mt)) was significantly lower in summer C. ornata (24.1 ± 0.50 μm² μm⁻³) than both winter C. ornata (32.3 ± 0.95 μm² μm⁻³) and N. concinna (34.3 ± 4.43 μm² μm⁻³). The surface area of mitochondrial cristae per unit fibre volume was significantly higher in N. concinna, due largely to the greater mitochondrial volume density. These results and previous studies indicate that mitochondrial proliferation in the cold is a common, but not universal response by different species from different thermal habitats. Seasonal temperature decreases on the other hand, leading preferentially to an increase in cristae surface density. Stereological measures also showed that energetic reserves, i.e. lipid droplets and glycogen in the pedal muscle changed greatly with season and species. This was most likely related to gametogenesis and spawning.     

Nutritional and related experiments on laboratory maintenance of three species of symbiont-bearing,large foraminifera

Factors were examined that affect survival and growth of two common species of large foraminifera from the Red Sea,Amphisorus hemprichii Ehrenberg andAmphistegina lobifera Larsen, 1976. The former is host for dinoflagellate and the latter for diatom zooxanthellae. Experimental conditions were modeled on conditions at 25 m during spring at Wadi Taba, Gulf of Elat, Israel, the season and site where the experimental organisms were collected between 1983 and 1988. The two species responded quite differently in nutritional experiments.A. hemprichii grew, on average, 0.270 mm in diameter in 3 mo on a diet ofNitzschia subcommunis Hustedt,Chlorella sp. (clone AT) orCylindrotheca closterium Rabenhorst isolated from their native habitat. Unfed controls did not grow. In contrast, unfed populations ofA. lobifera grew as well or better than those that were fed unialgal diets. Growth of both species was enhanced on particular mixed algal diets. Both species required photosynthetically active symbionts. Even when fed weekly and supplied with nutrients, neither species survived in the dark. All individuals ofA. hemprichii died after 8 wk incubation in the dark;A. lobifera survived longer, but all were dead by 13 wk. The highest growth rate ofA. hemprichii (0.037 mm wk^–1) was obtained when they were fed, the medium was enriched, and the medium was changed weekly. All other conditions being the same, growth rate dropped to 0.009 mm wk^–1 when the medium was changed every 3 wk. In contrast,A. lobifera grew fastest when the medium was changed every 3 wk. Food or enrichment with nitrate or phosphate did not stimulate growth (0.03 mm wk^–1) over that of the controls. Specimens ofMarginopora kudakajimensis Gudmundsson from Japan, another dinoflagellate-bearing species, were also tested. They grew best (0.02 mm wk^–1) when cultured in light, in media enriched with nitrate and phosphate changed weekly, and fed. All three species withdrew nitrate and phosphate from the medium in chemostat experiments.     

Three beetles—three concepts. Different defensive strategies of congeneric myrmecophilous beetles

Myrmecophiles, i.e., organisms associated with ants live in a variety of ecological niches in the vicinity or inside ant colonies and employ different strategies to survive ant encounters. Because different niches are characterized by different encounter rates with host ants, strategies used to avoid ant aggressions should depend on these niches. This hypothesis was studied with three rove beetle species of the genus Pella, which are myrmecophiles of the ant Lasius fuliginosus and the non-myrmecophilous relative Drusilla canaliculata. Behavioral tests in the field revealed that Pella species are better adapted to interactions with ants than D. canaliculata, but that they use species-specific strategies in ant interactions. Pella cognata and Pella funesta avoid encounters with ants by swift movements. Chemical analyses of the defensive tergal gland secretions showed that P. cognata has replaced the aggression inducing undecane by the behaviorally neutral tridecane. P. funesta repels the ants by releasing the panic alarm pheromone sulcatone from its tergal gland resulting in an “ant free space” around the beetles. Finally, Pella laticollis uses a specific and unique appeasing behavior. Behavioral and chemical data did not reveal any indication for the mimicry of the ants' cuticular hydrocarbon profiles by any of the beetle species. It is discussed that the employed strategies correlate with the ecological niches of the beetles. P. cognata and P. funesta are living along ant trails with ample space to escape and the employed strategies are probably sufficient to escape from dangerous conflicts. In contrast, P. laticollis lives in refuse areas of ant nests with frequent ant encounters, and its appeasement strategy allows it to stay at the encounter site.     

Demonstration of sex pheromones in the predaceous diving beetle Rhantus suturalis (MacLeay 1825) (Dytiscidae)

Sex pheromones are used by a wide variety of species in terrestrial ecosystems. Much less is known about these pheromones in aquatic systems e.g., for diving beetles. To test the use of pheromones and visual signals for mate finding by the diving beetle Rhantus suturalis (MacLeay 1825), behavioral experiments were performed using three different types of vessels containing conspecific. In experiments with non-permeable glass flasks, which did not allow the diffusion of chemical substances, males and females did not stimulate any reaction by conspecific of either sex. In experiments with opaque but water permeable vessels, and in experiments with vessels made of finely woven steel, which allowed the perception of chemical as well as optical cues, male diving beetles were significantly attracted to females. Females were attracted to other females only in the last experiment, when simultaneously perceiving chemical and optical cues. These results indicate that R. suturalis females release sex pheromones to attract mating partners, which is the first experimental demonstration of pheromones in the Dytiscidae.