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R A Johnstone

Publications and source records attributed to R A Johnstone.

9 recordsLinked to original sources
PubMed1992

Variation across species in the size of the nuclear genome supports the junk-DNA explanation for the C-value paradox.

The amount of DNA in the nuclear genome (the DNA C-value) of eukaryotes varies at least 80,000-fold across species, and yet bears little or no relation to organismic complexity or to the number of protein-coding genes. This phenomenon is known as the C-value paradox. One explanation for the C-value paradox attributes the size of the nuclear genome to 'junk' (typically non-coding) genetic elements that accumulate until the costs to the organism of replicating excess DNA select against it. Across species, organisms that develop at a slower rate should tolerate more junk DNA. Alternatively, junk DNA may function as a nucleo-skeleton to maintain the volume of the nucleus at a size proportional to the volume of the cytoplasm in the cell. Across species, the DNA C-value is predicted to vary with the nuclear and cytoplasmic volumes of cells. Previous studies have not been able to distinguish between the skeletal-DNA and junk-DNA explanations for the C-value paradox. We report a study of DNA content in 24 salamander species which does. The size of the nuclear genome is correlated with developmental rate even after the effects of nuclear and cytoplasmic volume have been removed. However, genome size is not correlated with cytoplasmic volume after controlling for developmental rate. These results support the view that junk DNA accumulates in the nuclear genome until the costs of replicating it become too great, rather than that it functions as a nucleo-skeleton.

Animals↗
PubMed1992

Error-prone signalling.

The handicap principle of Zahavi is potentially of great importance to the study of biological communication. Existing models of the handicap principle, however, make the unrealistic assumption that communication is error free. It seems possible, therefore, that Zahavi's arguments do not apply to real signalling systems, in which some degree of error is inevitable. Here, we present a general evolutionarily stable strategy (ESS) model of the handicap principle which incorporates perceptual error. We show that, for a wide range of error functions, error-prone signalling systems must be honest at equilibrium. Perceptual error is thus unlikely to threaten the validity of the handicap principle. Our model represents a step towards greater realism, and also opens up new possibilities for biological signalling theory. Concurrent displays, direct perception of quality, and the evolution of 'amplifiers' and 'attenuators' are all probable features of real signalling systems, yet handicap models based on the assumption of error-free communication cannot accommodate these possibilities.

Animal Communication↗
PubMed1992

The continuous Sir Philip Sidney game: a simple model of biological signalling.

An analysis of Maynard Smith's two-player, ESS model of biological signalling, the "Sir Philip Sidney game", is presented. The stable strategies of the players in this game are shown to satisfy the conditions of Zahavi's handicap principle. At equilibrium, signals are honest, costly, and costly in a way that is related to the true quality revealed. Further analysis reveals that the level of cost required to maintain stability is inversely related to the degree of relatedness between the players. It therefore seems likely that stable biological signalling systems will feature lower signalling costs when communication occurs between relatives. A three-player, extended version of the model is investigated, in which signals are passed via an intermediate, or "messenger". It is shown that this destabilizes the signalling system, and leads to increased signalling costs. This result suggests that "kin conflict" theories of the evolution of the endosperm in flowering plants require further refinement. The introduction of a novel resource acquisition tissue, which mediates parent-offspring interaction during development, cannot be assumed to limit parent-offspring conflict simply because it carries an extra copy of the maternally inherited genes. The ability to add such complications to the Sir Philip Sidney game and still obtain solutions makes it a very useful modelling tool.

Animals↗
PubMed1989

A review of fatal road accidents in Oxfordshire over a 2-year period.

The records of 131 road accident fatalities which occurred in Oxfordshire over a 2-year period were reviewed. Aspects of the accident circumstances, the injuries incurred and the cause of death were examined. The majority of fatal accidents occurred during daylight hours and in dry weather. Deaths were mainly due to cerebral injury (34.4 per cent) or uncontrollable (mainly thoracic) haemorrhage (25.2 per cent), or a combination of both (8.4 per cent). A number of deaths occurred in hospital from complications rather than from the injury itself. In addition to this, there were four deaths from natural causes. Where death occurred at the scene of the accident, blood alcohol levels were determined. Almost 50 per cent of the drivers for whom a level was obtained had measurable alcohol in their bloodstream, and 28 per cent of such drivers were over the legal limit. Three cases who reached hospital alive were, on review, assessed to have potentially survivable injuries, and a further two patients died in the post-accident period of potentially survivable complications.

Accidents, Traffic↗
PubMed1989

Biomechanical aspects of pelvic and hip injuries in road traffic accidents.

The mechanism of pelvic fractures has been well documented from radiographs but little is known of the forces required to produce these injuries. We examined 40 cases of pelvic injury sustained in road traffic accidents where the direction of impact and the velocity differential was known. In frontal impacts, indirect shear injuries of the pelvis were prominent, while in side impacts, lateral compressive injuries occurred. With increasing velocity differentials and vehicle deformation and intrusion, more severe pelvic injury occurred, often in association with significant head, chest, and lower limb injuries. Side impacts were noted to produce more severe injuries at lower velocity differentials when compared with frontal crashes.

Accidents, Traffic↗