THE PRODUCTION OF PARTHENOGENETIC MAMMALIAN EMBRYOS AND THEIR USE IN BIOLOGICAL RESEARCH

1. The eggs of many mammalian species show signs of early parthenogenetic development as they age after ovulation and oocytes may form transplantable terato-carcinomas. These cases of apparently spontaneous parthenogenetic development suggest that the cells of the female germ line have an inherent tendency to divide and differentiate. 2. The ovulated eggs of virgin female mammals may be stimulated to start parthenogenetic development by a wide variety of treatments. Most of these damage the egg so that it does not develop beyond the 4 cell stage. However if the eggs are exposed to electrical activation, hyaluronidase treatment, or temperature shock then in many cases they will develop into blastocysts. 3. These blastocysts may be either haploid or diploid. Haploid blastocysts may be formed either by the egg extruding the nucleus of the second polar body or by the egg dividing in half, so that the female pronucleus is in one cell and the nucleus of the second polar body is in another cell. Diploid blastocysts are formed by the retention of the nucleus of the second polar body within the egg. The way in which the egg develops may be controlled by altering the osmolarity of the culture medium, the age of the egg at the time of activation, or the strain of animal used. 4. The action of the sperm on the egg can be defined by comparing the events of normal fertilization and parthenogenetic activation. Both these stimuli cause the egg to expose binding sites for Concanavalin A to synthesize DNA and to divide. However, the release of cortical granules, which occurs after fertilization, does not appear to be induced by parthenogenetic activation, and it is significant that parthenogenones lack the sperm nucleus and mitochondria. 5. The majority of parthenogenones die soon after implantation. Death at this time occurs with parthenogenones obtained from the activated eggs of both inbred and outbred stocks. Death might be caused by recessive lethal mutations or by extra-genetic effects of the maternal chromosomes. 6. Parthenogenones contain endogenous A-type particles which shows that these bodies are inherited through the female germ line. 7. Parthenogenones may in the future provide both a method for chromosome mapping and a source of haploid cells. At present the use of mammalian parthenogenones in biological research is restricted by the heavy embryonic losses which occur around the time of implantation. This means that the role of the sperm, gene activity and virus expression must be studied during a very limited period. Part of the mortality before implantation is the consequence of the damage which the egg suffers during activation and it should be possible to reduce this loss by improving the techniques for activation. It may also be possible to increase the quantity of cells derived from haploid and diploid mammalian embryos by deriving teratocarcinomas from them.     

THE COLLECTION OF FOUND IVORY IN MURCHISON FALLS NATIONAL PARK, UGANDA

The paper concerns the circumstances surrounding the collection of ivory from dead elephants, with particular reference to Murchison Falls National Park. The characteristics of the interval between death and complete disintegration of an elephant are described. These, combined with observations of known age skeletons, comprised the criteria used in classifying skeletons found from the air into three relative age classes. Average annual mortality is estimated for the population north of the Nile (MFPN) at 147 animals yielding 1945 kg of ivory, and for that south of the Nile (MFPS) at 474 animals yielding 7497 kg ivory. Park-found ivory records are analyzed for the 11 y 1959–69. The expected age distribution of deaths is compared with the observed. For MFPN a bias in favour of large (male) tusks is present, explicable by the concentration of ranger search effort in areas of known high male density. For MFPS a bias towards small tusks is thought to be caused by elephants wounded outside the park dying inside it. The National Park recovers an average of 27.6 % of its available ivory per annum, with large annual fluctuations probably correlated with the incidence of wounding outside the park. High losses to poachers are evident. An aerial search for ivory showed a tendency for elephants to die near watercourses. A finding rate of one carcass every 4.3 km of watercourse was obtained. As only 5 % of carcasses still had tusks the aerial searching was prematurely terminated. The results indicated a finding efficiency of 26.4% of the available current year carcasses. Comparative costing suggests that ground searching would be a more efficient method of finding ivory than aerial searching. The high value of the available ivory in Murchison and other areas justifies intensive searching. The low collection rates prevailing in East Africa are largely attributable to the absence of appropriate search efforts.     

Growth Regulation of Galium mollugo L. Cell Suspensions by a-Naphthalene Acetic Acid

Fidgeon, C. and Wilson, G. 1987. Growth regulation of Galiummollugo L. cell suspensions by -naphthalene acetic acid.—J.exp. Bot. 38: 1491–1500. Galium mollugo cell suspension cultures were found to requirethe plant growth regulator -naphthalene acetic acid (-NAA) forcontinued growth and cell division. This requirement could notbe substituted in either batch or semi-continuous culture byindole-3-acetic acid (IAA) or 2,4-dichlorophenoxy acetic acid(2,4-D) at any concentration tested. However, ß-naphthaleneacetic acid (ß-NAA) and indole-3-butyric acid (IBA)were found to support growth when supplied at a concentrationtwo orders of magnitude greater than the normal media level(0–5 mg dm³). The growth of Galium cells was found to be influenced not onlyby the -NAA initially supplied in the medium but also by theexposure to -NAA in previous growth cycles. Preculture of cellsfor 3 d in an -NAA containing medium, followed by cell washingand re-inoculation into -NAA free medium, supported a quantitativegrowth response similar to that obtained after 14 d in the control-NAA containing medium. Even short-term exposures between 0·5and 6·0 h stimulated a detectable growth response 14d later. These observations raise questions relating to theuptake and perception of exogenously supplied growth regulatorsby cultured cells. The delayed kinetics of this form of response is of significancein culture regimes in which cells are transferred from one mediumto another, differing in their growth regulator composition,in order to induce morphogenesis     

Comparison of the Surface Proteins and Glycoproteins On Erythrocytes of Calves Before and During Infection With Babesia Bovis

The surface proteins and glycoproteins on red cells from normal and Babesia bovis-infected calf blood have been compared. Several radiolabeling probes were used to label specifically external membrane molecules which were then separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and identified by autoradiography or fluorography. No differences were observed among the Coomassie Blue-stained membrane proteins of erythrocytes from individual uninfected calves. Comparison of red cells from these animals also indicated no qualitative differences in the surface proteins with accessible tyrosyl residues labeled by lactoperoxidase-catalyzed radioiodnation, although some quantitative variation in the uptake of radioactivity into particular proteins was observed. the major radioiodinated bands on normal bovine erythrocytes had Mr of 165, 130, 90, and 45 kiloDaltons. However, labeling of surface glycoproteins by the periodate/[³H]NaBH₄ and galactose oxidase (± neuraminidase)/[³H]NaBH₄ methods showed significant differences in the surface proteins of red cells from individual uninfected calves. of 14 animals tested, 5 had major labeled glycoproteins of unique Mr. No changes were observed in radioiodinated surface proteins of total red cell samples from infected calves with 0.5-6% parasitemia. Radioiodination of concentrated infected red cells from the same samples (concentrated by selective hypotonic lysis of uninfected erythrocytes in KC1) resulted in the labeling of 3 new surface proteins, with Mr of 118, 115, and 60 kiloDaltons. the same new ¹²⁵I-labeled bands were identified on infected cells from 3 avirulent strains of B. bovis used in vaccine production. Furthermore, in concentrated infected cells there was very poor radiolabeling of major bands strongly labeled on uninfected cells (Mr 165, 130, and 90 kiloDaltons), suggesting parasite-induced loss of these proteins. Although there were some differences in ³H-labeled surface glycoproteins of red cells from normal and. B. bovis -infected blood, they were restricted to minor labeled bands and were not seen consistently. the labeled surface glycoproteins of concentrated infected cells were very similar to those of the uninfected red blood cells from infected blood.     

The foraging behaviour of Australian honeyeaters: a review and some comparisons with hummingbirds

The foraging behaviour of Australian honeyeaters is reviewed in terms of diet, foraging selectivity, foraging flight mode, quality and quantity of nectar encountered per flower, flower densities encountered and effect of predation. At the same time comparisons are made between honeyeaters and hummingbirds. These two groups of birds are superficially similar. Both feed on nectar and insects. Both tend to have long curved bills and tongues adapted for removal of nectar from flowers. Both tend to feed at long, red flowers. However, on close inspection, honeyeaters and hummingbirds are quite dissimilar. For example, many honeyeaters include fruit in their diets. Hummingbirds almost never eat fruit. Honeyeaters appear to be considerably less nectarivorous and more insectivorous than hummingbirds. Honeyeaters are, for the most part, larger than hummingbirds and they usually perch while feeding whereas hummingbirds usually hover. Honeyeaters but not hummingbirds often flock while feeding. Predation appears to be considerably more important for honeyeaters than for hummingbirds. Territorial defense of flowers seems common in hummingbirds but uncommon in honeyeaters. These differences are discussed in detail and explanations are offered for them wherever possible.     

Dynamic Properties of Giant Muscle Fibers of the Barnacle

Giant muscle fibers of the barnacle give graded, relativelyslow contractions, A plateau level, termed the unit response,occurs with stimuli of 3 msec, but pulses longer than 10–15msec give much greater tension or shortening. Repetitive stimulationwith pulses of 3 msec leads to a tetanus. The magnitude of activestate was determined, and found to be also graded in natureand slow to develop, though early in onset. The full developmentof active state requires 80–120 msec. A high level ofeffective series-elasticity was associated with the sarcomeresthemselves.     

Gregarious flowering in a lowland tropical rainforest: A possible response to disturbance by Cyclone Winifred

Observations in tropical lowland rainforests damaged by Cyclone Winifred on 1 February 1986 suggest that the disturbance has been followed by an unusual burst of flowering. Fifty-four species of concurrently flowering shrubs and trees were recorded in early March along a 4 km road transect in a cyclone-damaged forest. Approximately 80% of the smaller tree and shrub species observed were flowering. Twelve species which had flowered and fruited prior to the cyclone flowered again. Some species which normally flower following periods of partial or complete deciduousness in the drier months of the year flowered after being defoliated by the cyclone. Widespread defoliation of the rainforests, together with the hot, dry weather which followed the cyclone, exposed the understorey layers to abrupt increases in temperature, insolation, and water stress. It is postulated that these environmental changes may have effected the synchronization of flowering of a larger number of species than would normally occur. It is suggested that longterm changes in the species composition of the damaged forests as a result of coincidences of seed availability and regenerative space may occur.     

Vision and the foraging technique of skimmers (Rynchopidae)

In birds, the position and extent of the region of binocular vision appears to be determined primarily by feeding ecology. Of prime importance is the degree to which vision is used for the precise control of bill position when foraging. Skimmers (Rynchops, Rynchopidae, Charadriiformes) exhibit a unique foraging behaviour and associated structural adaptations. When foraging they fly low and straight over water with the mouth open and the mandible partially submerged. Items that are hit by the lower mandible are grasped by a rapid reflex bill closure. It is believed that this unique ‘skimming’ foraging technique is guided by tactile rather than visual cues. It is predicted therefore that the visual fields of skimmers will have similar topography to those of other tactile feeding birds. We determined retinal visual fields in Black Skimmers Rynchops niger using an ophthalmoscopic reflex technique. Contrary to expectation the visual fields of Black Skimmers are not like those of other tactile feeders. They show high similarity with those of birds that feed by precision‐pecking. The projection of the bill tip when the mouth is closed and when open (as in skimming) falls within the frontal binocular field and there is an extensive blind area above and behind the head. We argue that this visual field topography functions to achieve accurate bill positioning with respect to the water surface when skimming and, because foraging skimmers cannot determine the identity of what they are seizing as they skim, to permit the visual identification of prey items held between the mandibles after they have been taken from the water surface. When skimming, only a small portion of the binocular field, approximately 5° wide and extending 5° above the horizontal, looks in the direction of travel. The small size of this forward‐facing region of binocularity in skimmers suggests that control of locomotion in birds does not necessarily require extensive binocularity in the direction of travel.     

Chlorsulfuron Reduces Extension of Wheat Root Tips in Low-zinc Solution Culture

Root tip extension was used as a measure of wheat root responseto exposure to the sulfonylurea herbicide chlorsulfuron. Plantspre-grown in low-zinc (0.2 µMZnHEDTA) solutions were placedin a perspex chamber with nutrient solution on both sides ofa partition separating the root tip from the rest of the plant.The root tip was exposed to different concentrations of chlorsulfuronand observations were made during 22 h. Increasing the concentrationof zinc in the solution around the root tip to 4 µMZnHEDTAdid not alter root tip extension in the absence of chlorsulfuron.Significant decreases in root growth after 22 h were obtainedwith concentrations of 120 µg chlorsulfuron l^-1and greater.Increasing the Zn concentration from 0.2 to 20 µMZnHEDTAin the nutrient solution around the root tip decreased controlroot growth but stimulated chlorsulfuron-treated roots to extendat the same rate as chlorsulfuron-free control plants. AddingZn and chlorsulfuron to the more mature root parts above theroot tip partition did not significantly influence root tipextension. It is concluded that chlorsulfuron inhibits wheatroot growth and that increased Zn concentrations can alleviateor prevent the deleterious effects of chlorsulfuron.Copyright1998 Annals of Botany Company Wheat,Triticum aestivumL., chlorsulfuron, root growth, zinc.