Physicochemical stream bed characteristics and recruitment of the freshwater pearl mussel (Margaritifera margaritifera)

1. The freshwater pearl mussel (Margaritifera margaritifera) is endangered and of conservation importance. We used its survival/mortality during the critical post‐parasitic phase as a biological indicator for the habitat quality of the stream substratum. 2. We established and tested biological, physical and chemical methods of assessing the stream bed in 26 streams from seven European countries. We analysed penetration resistance, texture, the concentrations and ratios of C, N, S, P, Fe, Mn in fine material <100 μm, and redox, pH and electric conductivity at the surface and at 5 and 10 cm into the substratum. 3. Sites with high stream bed quality (promoting pearl mussel populations with good juvenile recruitment) had coarser and better sorted substrata with significantly lower quantities of fines, and a higher Mn concentration in the fines, than poor quality sites. Redox potential (Eh) at sites without recruitment differed markedly between the free‐flowing water at the surface and at 5 and 10 cm in the bed, whereas no differences were detectable at good quality sites. This was also true of electric conductivity and, to a lesser extent, pH. The stream bed at sites lacking pearl mussel recruitment had a more variable and higher penetration resistance, indicating clogging of the interstitial macropore system by the deposition of mud and compaction of the stream bed. 4. Our results show that habitat quality for pearl mussels depends strongly on the exchange between the surface and the interstices, which is governed by physicochemical characteristics of the stream substratum. Combined measurements of penetration resistance, depth gradients of Eh and texture were most suitable for assessing stream bed quality, while water chemistry was insufficient because of the decoupling of interstitial and free‐flowing water at poor quality sites.     

Enrichment of human bone marrow mononuclear phagocytes and characterization of macrophage subpopulations by immunoenzymatic double staining

In order to isolate and enrich bone marrow mononuclear phagocytes, we performed magnetic-activated cell sorting using beads coupled to a monoclonal antibody directed against the monocyte/macrophage surface molecule CD14. Co-localization of antigens in single cells was achieved by combining an alkaline phosphatase--anti-alkaline phosphatase and an avidin--biotin complex immunoassay, avoiding the use of peroxidase. Bone marrow macrophages were first labelled by the monoclonal antibody PG-M1 (anti-CD68). Subsequently, cytoplasmic and/or surface double staining by the monoclonal antibodies against HLA-DR and Mac-2 antigen or the lectin GSA-I-B4 was carried out. Whereas HLA-DR was co-expressed by the great majority of PG-M1+ macrophages (84.9% +/- 6.9%), only a subpopulation exhibited Mac-2 (69.9% +/- 5.9%) antigen or galactoside structures detected by GSA-I-B4 (65.0% +/- 6.7%). The latter result differed only slightly from the percentage of GSA-I-B+4 macrophages determined in a previous comparative immunomorphometrical study. Therefore, using our method of isolation and enrichment by magnetic-activated cell sorting, only a negligible portion of macrophages is apparently stimulated, as shown by GSA-I-B4 staining. This methodology seems to be a valuable tool for further studies on the monocyte--macrophage system. © 1998 Chapman & Hall     

Beyond gradual warming: extreme weather events alter flower phenology of European grassland and heath species

Shifts in the phenology of plant and animal species or in the migratory arrival of birds are seen as ‘fingerprints’ of global warming. However, even if such responses have been documented in large continent‐wide datasets of the northern hemisphere, all studies to date correlate the phenological pattern of various taxa with gradual climatic trends. Here, we report a previously unobserved phenomenon: severe drought and heavy rain events caused phenological shifts in plants of the same magnitude as one decade of gradual warming. We present data from two vegetation periods in an experimental setting containing the first evidence of shifted phenological response of 10 grassland and heath species to simulated 100‐year extreme weather events in Central Europe. Averaged over all species, 32 days of drought significantly advanced the mid‐flowering date by 4 days. The flowering length was significantly extended by 4 days. Heavy rainfall (170 mm over 14 days) had no significant effect on the mid‐flowering date. However, heavy rainfall reduced the flowering length by several days. Observed shifts were species‐specific, (e.g. drought advanced the mid‐flowering date for Holcus lanatus by 1.5 days and delayed the mid‐flowering date for Calluna vulgaris by 5.7 days, heavy rain advanced mid‐flowering date of Lotus corniculatus by 26.6 days and shortened the flowering length of the same species by 36.9 days). Interestingly, the phenological response of individual species was modified by community composition. For example, the mid‐flowering date of C. vulgaris was delayed after drought by 9.3 days in communities composed of grasses and dwarf shrubs compared with communities composed of dwarf shrubs only. This indicates that responses to extreme events are context specific. Additionally, the phenological response of experimental communities to extreme weather events can be modified by the functional diversity of a stand. Future studies on phenological response patterns related to climate change would profit from explicitly addressing the role of extreme weather events.     

Control of the horizontal flight-course by air-current sense organs in Locusta migratoria

ABSTRACT. The role of the air-current sense organs of Locusta migratoria (the antennae and the hair fields on the frons and vertex of the head) in control of the horizontal flight-course in relation to the air was investigated in locusts flying tethered on a torque gauge. The antennae were apparently not of importance in the control of flight direction in the horizontal plane. If the hair fields were stimulated by an air current from either side, however, a torque on the vertical body axis was generated by the beating wings after a reaction time of at least 0.1 s. In free flight this would result in a yaw, bringing the animal back in line with the air stream. This torque reaction will stabilize the flight direction in the horizontal plane via a negative feedback mechanism, the hair fields above the lateral ocelli being the feedback receptors. In free flying locusts a torque on the vertical body axis can be generated by both the beating wings and the abdomen working as a rudder when bent to either side. The wings, however, are dominant in the reflex stabilization of the flight-course.     

Three-Dimensional Reconstruction of a Dictyosome using Serial Sections

A single dictyosome from a suspension cultured sycamore cellhas been reconstructed on an enlarged scale using electron micrographsobtained from a series of 12 thin sections as the basis forthe moulding of profile slices. Slices were hardened and stucktogether to form single cisternae, tubules and vesicles. Thesestructural elements were joined, true-to-scale, to give a three-dimensionalfigure. The model thus obtained is more realistic than otherwell-known dictyosomal models previously presented in the literature.In contrast to these our model exhibits occasional membranecontinuities between adjacent cisternae of the dictyosomal stackand entertains the possibility of similar connections betweencisternae of the endoplasmic reticulum and the Golgi apparatus. Key words: Acer pseudoplatanus, Dictyosome reconstruction