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Organisms have evolved diverse behavioural strategies that enhance the likelihood of encountering and assessing mates

The ability to recognize individuals is essential to many aspects of social behaviour, such as the maintenance of stable social groups, parent-offspring or mate recognition, inbreeding avoidance and the modulation of competitive relationships. Odours are a primary mediator of individuality signals among many mammals. One source of odour complexity in rodents, and possibly in humans, resides in the highly polymorphic major histocompatibility complex (MHC). The olfactory acuity of mice and rats allows them to distinguish between the urinary odours of congenic strains differing only in single genes within the MHC, although the chemical mediators or odorants are unknown. However, rodent urine also contains a class of proteins, termed major urinary proteins (MUPs), that bind and release small volatile pheromones. We have shown that the combinatorial diversity of expression of MUPs among wild mice might be as great as for MHC, and at protein concentrations a million times higher. Here we show in wild house mice (Mus domesticus) that urinary MUPs play an important role in the individual recognition mechanism.

A recent study1 of the surface manifestation of incremental lines associated with enamel formation suggested that the crowns of early hominid incisor teeth were formed more rapidly than those of modern humans. In the absence of comparative data, the authors were forced to assume that enamel increments in fossil teeth were similar to those in modern humans. We have used evidence from the fractured surfaces of molar teeth to deduce estimates for both long- and short-period incremental growth markers within enamel in east African 'robust' australopithecine and early Homo teeth. We conclude that in these early hominids, crown formation times in posterior teeth, particularly in the large thick enamelled2 molar teeth of the east African 'robust' australopithecines, were shorter than those of modern humans. This evidence, considered together with data on crown and root formation times in modern apes3, suggests that the posterior teeth in these hominids both formed and erupted more rapidly than those of modern man. These results have implications for attempts to assess dental and skeletal maturity in hominids.

THE most striking and important feature of members of the genus Rhizobium is their ability to nodulate and fix nitrogen in the roots of legumes. There is specificity in this interaction. Legumes belonging to one cross-inoculation group are nodulated only by certain classes of Rhizobium and indeed Rhizobium species are defined in terms of the host legumes that they can nodulate—for example, R. leguminosarum nodulates peas, R. trifolii nodulates clover and R. phaseoli nodulates beans of the genus Phaseolus. The genetic bases of the nodulation process and of host specificity are poorly understood. Many Rhizobium strains harbour plasmids1–4 and genetic evidence has suggested that such plasmids might carry some of the information required for the development of the symbiosis5,6. We report here that the ability to nodulate peas can be transferred at high frequency from a strain of R. leguminosarum to a non-nodulating strain of R. leguminosarum and to three other species of Rhizobium that nodulate legumes other than peas. We infer from this that some of the genetic information required for nodulation is plasmid-linked.

Zone plate shadow casting is a complementary technique to the Leith–Upatnieks modification of Gabor's interferometric method for producing holograms1,2. Suggested originally by Mertz3 in 1961 for use in X-ray astronomy, the technique has received considerable attention in nuclear medicine4 for imaging radioactive organs via emitted X-rays and γ-rays and, more recently, for examining in a tomographic sense the microscopic spatial source distributions of X rays and charged particles in laser-produced plasmas5. A series of simple experiments are described here which demonstrate that zone plate encoded neutron holography can be used to image objects. An object placed in a cold neutron beam from a research reactor scatters neutrons through a Fresnel zone plate, with alternate zones of gadolinium and aluminium, which produces a hologram of the object on an X-ray film. The image is constructed by placing the hologram, linearly reduced in size, in a converging laser beam which produces a real image of the original object. Results are presented for two objects, a pair of 0.01 m diameter rubber spheres and a 0.04 m square Maltese cross made from poly-tetrafluoroethylene (PTFE).

IN an experiment on radio propagation which is currently being flown in the British Skylark rocket, pulse signals on frequencies in the range 2–10 Mc/s are radiated from a ground based transmitter T (Fig. 1) and the pulse pattern received at the rocket R is telemetered back to ground. An additional very high frequency (104 Mc/s) pulse is also radiated from the ground and received at the rocket so that both the true path and group path are measured simultaneously. Pulse patterns are recorded at 1/50 sec intervals throughout flight and provision is made for switching to different selected frequencies when required. Time base scans on coarse and fine scales enable the overall pattern to be studied and the time separation between the various pulses to be measured accurately. A typical pulse pattern is shown in Fig. 2a which for clarity is reproduced as a line tracing in Fig. 2b. In this example, pulse A is the VHF 104 Mc/s signal, pulse B the direct HF (3.6 Mc/s) signal and the broader pulse C is the indirect echo signal reflected from the F layer.

ALTHOUGH the main temporal variations in the ionosphere show a very large measure of solar control, it has long been recognized that some ionospheric phenomena have features which strongly suggest a non-solar origin or control. One such example is the ‘winter anomaly’ in ionospheric absorption. Thus a recent survey1 snows that this phenomenon seems to have a definite regional character in that although on any one day it may extend over areas of at least 106 km2 its enhancement in one longitude zone appeared to correspond to a diminution in its intensity in another longitude zone. Recently there has been clear evidence that at least part of this ‘winter anomaly’ is to be associated with abnormal warmings in the stratosphere at levels of about 30 km. Convincing evidence for such a relationship has been found in some recent work by Shapley and Beynon at Aberystwyth (preceding communication). As part of a broader consideration of this problem we have examined the seasonal variation in various parameters at different levels in the atmosphere and these are briefly reported below.

New studies on the jaws of hominids, based on incremental growth markings in teeth, can now provide an absolute timescale with which to calibrate dental developmental events such as tooth emergence. These new estimates of crown-formation times and the observed sequences of dental development are different in the hominids Australopithecus and Paranthropus. Early hominids evidently had shorter periods of dental development than modern humans and therefore a less prolonged infancy.

Studies using 13C-enriched precursors in combination with carbon magnetic resonance spectroscopy have established the biosynthetic origin of most of the carbon atoms present in rifamycin S and suggest a common scheme for ansamycin biogenesis.

Application of an Agar–Agar Diffusion Procedure to Pesticide Residue Analysis and to the Cholinesterase Screening of Candidate Pesticides