The fossil record of Limopsis (Bivalvia: Limopsidae) in Antarctica and the southern high latitudes

Abstract: Limopsis is one of the most speciose and widespread bivalve genera in the Southern Ocean at the present day. However, the fossil record of the genus is poorly known from the southern high latitudes. Here, we review the fossil record in this region to help understand the evolutionary origins of the genus. Limopsis infericola sp. nov. and additional specimens of a previously described species are added to the fossil record of Antarctica. The globally distributed limopsid clade had its earliest occurrences in the Early Cretaceous of Europe and New Zealand, then radiated during the Late Cretaceous (Maastrichtian, 70.6–65.5 Ma). Fossil evidence shows that the genus underwent a second, Cenozoic, radiation related to the isolation of Antarctica and the onset of cooling in the southern hemisphere. The genus has persisted in Antarctica for the last 50 myr, adapting to extreme changes in the environmental conditions, including surviving the last glacial maximum in marine refugia.     

Large-scale climatic signatures in lakes across Europe: a meta-analysis

Recent studies have highlighted the impact of the winter North Atlantic Oscillation (NAO) on water temperature, ice conditions, and spring plankton phenology in specific lakes and regions in Europe. Here, we use meta-analysis techniques to test whether 18 lakes in northern, western, and central Europe respond coherently to winter climate forcing, and to assess the persistence of the winter climate signal in physical, chemical, and biological variables during the year. A meta-analysis approach was chosen because we wished to emphasize the overall coherence pattern rather than individual lake responses. A particular strength of our approach is that time-series from each of the 18 lakes were subjected to the same robust statistical analysis covering the same 23-year period. Although the strongest overall coherence in response to the winter NAO was exhibited by lake water temperatures, a strong, coherent response was also exhibited by concentrations of soluble reactive phosphorus and soluble reactive silicate, most likely as a result of the coherent response exhibited by the spring phytoplankton bloom. Lake nitrate concentrations showed significant coherence in winter. With the exception of the cyanobacterial biomass in summer, phytoplankton biomass in all seasons was unrelated to the winter NAO. A strong coherence in the abundance of daphnids during spring can most likely be attributed to coherence in daphnid phenology. A strong coherence in the summer abundance of the cyclopoid copepods may have been related to a coherent change in their emergence from resting stages. We discuss the complex nature of the potential mechanisms that drive the observed changes.     

Gas exchange patterns of Pterostichus niger (Carabidae) in dry and moist air

Gas exchange patterns of adult male Pterostichus niger Schaller after hydration (i.e. given access to food and water) are compared in dry air [5–7% relative humidity (RH)] and moist air (90–97% RH) by means of flow‐through CO₂ respirometry combined with infrared probe actography. Of thirty beetles examined, slightly more than 50% showed continuous gas exchange and are not considered further. Of the remaining beetles, the majority (approximately 71%) display a pattern of cyclic gas exchange in both dry and moist air (i.e. CO₂ gas is released in bursts, with a low level of CO₂ release during the interburst periods). A minority of the beetles (four out of 30) are found to exhibit discontinuous gas exchange in both dry and moist air; this is characterized by three clearly separated states of the spiracles: closed (C), flutter (F) and open (O) phases. The pattern of cyclic gas exchange is associated with weak abdominal pulsations. After switching from moist to dry air, a small modulation of the discontinuous gas exchange cycles (maximum mean CO₂ production rate) occurs, providing no clear support for the hygric theory of discontinuous gas exchange in this species (i.e. that it serves to restrict respiratory water loss).     

Attachment forces of pea aphids (Acyrthosiphon pisum) on different legume species

1. Sympatric populations of insects adapted to different host plants are good model systems not only to study how they adapt to the chemistry of their food plant, but also to investigate whether morphological modifications evolved enabling them to live successfully on a certain plant species. 2. The pea aphid, Acyrthosiphon pisum (Harris) encompasses at least 11 genetically distinct sympatric host races, each showing a preference for a certain legume species. The leaflet surfaces of these legumes differ considerably in their wax coverage. 3. It was investigated whether the attachment structures of three pea aphid genotypes from different host races are adapted to the different surface properties of their host plants and whether they show differences in their attachment ability on the respective host and non‐host plants. 4. The surface morphology of plants and aphid tarsi was examined using SEM (scanning electron microscopy). The ability of the aphids to walk on specific surfaces was tested using traction force measurements. 5. The presence of wax blooms on the leaflets lowers the aphids' attachment ability considerably and diminishes their subsequent attachment on ‘neutral’ surfaces like glass. The pea aphid host races differ in their ability to walk on certain surfaces. However, the genotype from the adapted aphid host race was not necessarily the one with the best walking performance on their host plant. All aphids, regardless of the original host plant, were most efficient on the neutral control surface glass. The general host plant Vicia faba was the plant with the most favourable surface for all aphid host races.     

Genetic differentiation between populations of the European rose hip fly Rhagoletis alternata

We tested for genetic differentiation between populations of Rhagoletis alternata Fall. (Diptera: Tephritidae) on three different host species. We collected larvae from three rose species of the section Caninae ( Rosa canina L., Rosa corymbifera Borkh . , and Rosa rubiginosa L.) from 15 sites across Germany, where the three roses occurred together. Additionally, we sampled three sites in Switzerland. Roses differ in morphology (e.g. leaf glands) as well as phenology. We were able to score nine allozyme loci (five polymorphic). Populations from the three hosts did not differ in genetic variability. We found significant genetic differentiation between populations from different host species. However, the differentiation was very low (0.9%). Hence, we found no indication for host races. Furthermore, surprisingly little geographical structure of genetic differentiation was found between populations of this fruit fly across central Europe. We offer three mutually non-exclusive explanations for these findings. First, gene flow between populations of Rh. alternata is high. Second, the pattern of genetic differentiation is based on a recent expansion of the distributional range . Third, the ongoing gene flow between roses of the section Caninae acts as a hybrid bridge.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 90 , 619–625.     

Occurrence of the Parasitic Dinoflagellate Amoebophrya ceratii in Chesapeake Bay Populations of Gymnodinium sanguineum

Chesapeake Bay populations of the red-tide dinoflagellate Gymnodinium sanguineum were regularly infected by the parasitic dinoflagellate Amoebophrya ceratii during the summers of 1988–1991. Infections developed inside the nucleus of G. sanguineum and were always lethal to the host. Parasite generation time was ? 40 h at 23° C, with the intracellular, trophont phase lasting 39.5 ± 0.3 h, and the extracellular, vermiform stage persisting for ? 20 min. Near surface accumulations of G. sanguineum sometimes exceeded 1,000 cells/ml; however, host abundance was relatively low when integrated over the surface mixed layer of each station (mean = 12.2 cells/ml ± 2.96 SE; n = 60). Parasitized hosts were encountered in 75% of the samples where host abundance was ≥ 1 per ml, and epidemic outbreaks (20–40% hosts infected) were observed on several occasions. Epidemic infections were generally located several meters below surface accumulations of G. sanguineum and were always restricted to a narrow region near the pycnocline. Consequently, integrated station values for parasite prevalence were low, with an average 2.7% (± 0.31 SE; n = 60). Parasite induced mortality removed up to 8% of G. sanguineum populations per day, but averaged < 2% of host biomass throughout the Bay. Thus, parasitism by A. ceratii does not appear to be a major factor regulating G. sanguineum bloom in the main stem of Chesapeake Bay.     

Rhythms of passive and active ventilation, and circulation recorded in diapausing pupae of Mamestra brassicae using constant volume respirometry

Abstract.  The periodically occurring convective inflow of air into the tracheal system, or passive suction ventilation, together with the cyclic bursts of release of CO₂ and active ventilation, is recorded in diapausing pupae of Mamestra brassicae . A constant volume respirometer combined with an opto-cardiograph-actograph is used. In all pupae with a metabolic rate of 0.025–0.054 mL g⁻¹ h⁻¹, the bouts of almost imperceptible abdominal contractions are recorded during the bursts of carbon dioxide release and this mode of active ventilation is qualified as extracardiac haemocoelic pulsations. The pupae whose metabolic rate is 0.052–0.075 mL⁻¹ g⁻¹ h⁻¹ show more vigorous abdominal contractions. The results demonstrate that, in diapausing pupae, characterized with low metabolic rates, both passive suction ventilation, referred to also as passive suction inspiration, and active ventilation occurs. In approximately 50% of the pupae, each gas exchange microcycle during the interburst periods begins with a miniature PSI followed by a microburst of CO₂ release; in approximately 30% of the individuals, passive suction inspirations occur separately from CO₂ microbursts; in the remaining pupae, miniature ones without microbursts of CO₂ are recorded. A typical event is heartbeat reversion: in longer periods, the heart peristalses are directed forward (anterograde of heartbeat) and, in shorter periods, the heart peristalses are directed backward (retrograde of heartbeat). At 0 °C, the cyclic release of CO₂ and miniature passive suction inspirations during the interburst periods are preserved at lower frequencies but active ventilation is lost.