Wet season movements of individual wildebeests of the Serengeti migratory herd

Sixteen wildebeest were marked with radio transmitters and tracked for varying lengths of time during the period between late November, 1971, and mid-July 1972. They were repeatedly radiofixed from an aircraft prior to, during and after their annual wet season visit to the Serengeti Plain. Fix-to-fix tracks of animals showed that each hurried to the Plain at the onset of the rains, performed oscillatory movements over an individually distinct, elliptically shaped, fractional part of the Plain area, and departed into the woodland as the Plain dried out. Average fix-to-fix rate of travel approximated 3–75 km/day. Large aggregations of animals, armies, were smaller and more restless in the woodlands than on the Plain. Smaller aggregations included within armies, troops, varied in size as a function of activity. They were small when feeding and large when marching. Troops averaged larger in the woodlands mostly because they were more often marching there than on the plain. The tracked animals were equally successful in finding green forage in the presence of water in both habitats. The item in shortest supply appeared to be the presence of green forage in the woodlands and of water on the Plain. It is concluded that structural attributes of the woodlands, by lowering the security level of animals, played a part in making the Serengeti Plain attractive to the animals.     

Molecular Characterization of a Barley Gene Induced by Cold Treatment

A cDNA library was made from low positive temperature (6 ?C/2?C) grown barley shoot meristems. Several genes which are differentiallyexpressed, as measured by mRNA abundance, were selected fromthe library using a differential screen. This paper reportsan analysis of in vivo expression in several cultivars, theDNA sequence, copy number and chromosomal location of one gene(BLT14). In addition, genomic restriction fragment length polymorphismfor this gene in the 10 most widely UK-grown spring and 9 mostwidely UK-grown winter barley cultivars is analysed. Key words: Hordeum vulgare, low temperature, RFLP, differential expression, cDNA sequence     

Interactions between Marek's Disease Herpesvirus and Avian Leucosis Virus in Tissue Culture

A GROUP B herpesvirus is important in the aetiology of Marek's disease, a highly contagious lymphoproliferative disease of chickens^1,2. Chicks inoculated with enveloped Marek's disease herpesvirus (MDHV), extracted from feather follicle epithelium of chickens with the disease, developed tumour-like aggregates of lymphoid cells in the viscera and frequently in the peripheral nerves^3,4. Cultures of chicken embryo fibroblast (CEF) cells infected with MDHV develop discrete foci of altered cells⁵. Our data show that MDHV infection of cultures of CEF cells, previously infected with an avian leucosis virus (RAV-2), results in both a reduction in the number of MDHV foci and an increase in the complement fixing avian leucosis antigen (COFAL)⁶ titre.     

The effect of suspended clay on ciliate population growth rates

• 1 Renewed batch cultures of three algivorous and one bacterivorous ciliate showed that ciliate reproductive rates increase with increasing food concentration up to an asymptote. Maximum r_m values for Strobilidium gyrans, Bursaridium difficile and Euplotes eurystomus feeding on the cryptomonad alga Rhodomonas minuta were 0.87, 0.86 and 0.45 day-¹, respectively, while Paramecium aurelia feeding on the bacterium Enterobactor aerogenes had an r_m of 0.40 day-¹. B. difficile had a food threshold (r_m= 0) of 0.38 μg Cml-¹ and P. aurelia had a threshold of 1.6μg Cml-¹.
• 2 The presence of suspended fine (particle size <1 μm) and coarse (particle size 1–2μm) clay suppressed the half maximum reproductive rate of the ciliate Strobilidium gyrans by up to 69% but had no effect on B. difficile, E. eurystomus or P. aurelia. Populations of ciliates unaffected by clay may be released in situations where suspended particles negatively affect their metazooplankton predators and competitors.

     

Effects of forest clearcutting on leaf breakdown in a southern Appalachian stream

SUMMARY. Effects of forest clearcutting on rates of leaf breakdown were studied in Big Hurricane Branch, a second-order stream located at Coweeta Hydrologic Laboratory in the southern Appalachian Mountains of North Carolina, USA. Breakdown rates of leaves of three tree species were measured in the stream before, during and after the catchment was clearcut. Changes in the stream attributable to logging and associated activities—principally road building—were increased stream flow, increased sediment transport, elevated water temperatures, increased nitrate concentrations and decreased allochthonous organic inputs. Breakdown rates of all three leaf species were slowed during clearcutting and accelerated later. Following logging the breakdown rate of dogwood leaves was equal to the pre-treatment rate, and white oak and rhododendron leaves broke down faster than prior to treatment. We attribute the slow breakdown during treatment to burial of the leaf packs in sediment. Subsequent acceleration may have been due to a lack of alternative food sources for invertebrate detritivores.     

Xylem pathways in liana stems with variant secondary growth

FISHER, J. B. & EWERS, F. W., 1992. Xylem pathways in liana stems with variant secondary growth. The three-dimensional construction of stem xylem in tropical lianas (woody vines) was studied using several approaches: 1. observations of the xylem surface in stems with bark removed after NaOH treatment or natural retting; 2. reconstructions from serial transverse sections; 3. movement of dye solutions up isolated xylem sectors in intact plants, and 4. flow of dye solutions down branches and xylem sectors in isolated stem segments. Long distance (up to several metres) xylem pathways in unbranched stems and connections between lateral branches and main stems are described for !5 species in eight families which represented seven differnt patterns of secondary growth. The xylem in even the most complex stems is integrated by three-dimensional interconnections of xylem regions which may appear isolated in transverse section. Interconnections are most common at leaf and branch nodes. Some old stems have peripheral xylem that remains isolated over long distances in unbranched stems, but even these had structural and physiological interconnections between xylem regions at branch nodes.     

Proteins of the Crustacean Exoskeleton

We describe here some of the components of the exoskeleton ofthe decapod crustacean with emphasis on the constituent proteins,including both structural and enzymatic. All four layers, butparticularly the inner three, of the exoskeletons of four brachyuranscontain high concentrations of proteins 31 kDa; the innermostmembranous layer is especially rich in such proteins. A numberof crab exoskeletal proteins resemble insect cuticle proteinsin size (M_r) and isoelectric point (pI). A further similarityis the cross reactivity of crab exoskeletal proteins with fourdifferent antibodies against cuticular proteins of two speciesof insects. One of the small M_r exoskeletal proteins in theBermuda land crab Gecarcinus lateralis has a similar distributionas a protein of similar size in the cuticle of the tobacco hornworm Manduca sexta. The partial dissolution of an old exoskeletonand formation of the two outer layers of a new exoskeleton aremajor events in readying a crustacean for the increase in sizethat occurs at each molt. Expressing both parallel and sequentialactivation of a number of genes, a single layer of epidermalcells that bounds a crustacean such as G. lateralis synthesizesspecific proteins at different stages of the intermolt cycleas the outermost epicuticle and exocuticle are formed duringproecdysis and as the endocuticle and membranous layer are formedduring metecdysis. Finally, two sets of proteinases isolatedfrom integumentary tissues of land crabs degrade the same exoskeletalproteins in vitro as are degraded in vivo during proecdysis.     

Macroinvertebrate community structure,secondary production and trophic‐level dynamics in urban streams affected by non‐point‐source pollution

1. Despite non‐point‐source (NPS) pollution being perhaps the most ubiquitous stressor affecting urban streams, there is a lack of research assessing how urban NPS pollution affects stream ecosystems. We used a natural experimental design approach to assess how stream macroinvertebrate community structure, secondary production and trophic structure are influenced by urban NPS pollution in six streams. 2. Differences in macroinvertebrate community structure and secondary production among sites were highly correlated with stream‐water specific conductivity and dissolved inorganic phosphorus (DIP) concentrations. Macroinvertebrate richness, the Shannon diversity index and the Shannon evenness index were all negatively correlated with specific conductivity. These patterns were driven by differences in the richness and production of EPT and other intolerant taxa. Production of the five most productive taxa, tolerant taxa, non‐insect taxa and primary consumers were all positively correlated with stream‐water DIP. 3. Despite the positive correlation between primary consumer production and DIP, there was no correlation between macroinvertebrate predator production and either total or primary consumer macroinvertebrate production. This was observed because DIP was positively correlated with the production of non‐insect macroinvertebrate taxa assumed to be relatively unavailable for macroinvertebrate predator consumption. After removing production of these taxa, we observed a strong positive correlation between macroinvertebrate predator production and production of available prey. 4. Our results suggest that urban NPS pollution not only affects macroinvertebrate community structure, but also alters secondary production and trophic‐level dynamics. Differences in taxon production in our study indicate the potential for altered energy flow through stream food webs and potential effects on subsidies of aquatic insect prey to riparian food webs.