FLUCTUATING ASYMMETRY: AN EPIGENETIC MEASURE OF STRESS

(1) Fluctuating asymmetry (FA) is a useful trait for monitoring stress in the laboratory and in natural environments.
(2) Both genomic and environmental changes can increase FA which represents a deterioration in developmental homeostasis apparent in adult morphology. Genetic perturbations include intense directional selection and certain specific genes. Environmental perturbations include temperature extremes in particular, protein deprivation, audiogenic stress, and exposure to pollutants.
(3) There is a negative association between FA and heterozygosity in a range of taxa especially fish, a result consistent with FA being a measure of fitness.
(4) Scattered reports on non-experimental populations are consistent with experiments under controlled laboratory conditions. FA tends to increase as habitats become ecologically marginal; this includes exposure to environmental toxicants.
(5) In our own species, FA of an increasing range of traits has been related to both environmental and genomic stress.
(6) Domestication increases FA of the strength of homologous long bones of vertebrate species due to a relaxation of natural selection.
(7) FA levels are paralleled by the incidence of skeletal abnormalities in stressful environments.
(8) Increased FA is a reflection of poorer developmental homeostasis at the molecular, chromosomal and epigenetic levels.     

SELECTION, PREDICTION AND RESPONSE

1. The biometric approach to selection experiments has been outlined, and found to be rather deficient because it is based on excessively restrictive models which cannot take into account the complex architectures of quantitative traits as are being revealed today. 2. The nature of polygenes is discussed in detail from the theoretical point of view. In out breeding species, some form of the balanced polygenic complex is likely, showing polymorphism for the constituent genes. Although polymorphism is implicit in the argument, definitive evidence for poiymorphisms has only just appeared. 3. There is no evidence that polygenes differ from any other gene. 4. Several artificial selection experiments are described, in particular in Drosophila. By means of appropriate breeding techniques after obtaining responses to selection, genetic activity controlling quantitative traits can be located to chromosomes, and even specific loci found. Such few studies as have been carried out reveal, in general, the types of genetic architecture predicted on theoretical grounds. 5. Selection for behavioural traits is considered briefly and it appears that no new principles are needed, except that careful environmental control and objective measurement present problems. 6. The results of selection for quantitative traits in micro-organisms reveal similarities to results in higher organisms in the few cases where definitive work has been carried out. 7. Work on the simulation of models by computers has not greatly advanced selection experiment theory, mainly because, with few exceptions, linkage has been ignored. 8. The existing theory on which selection experiments are based is inadequate for several reasons. It cannot predict the rate of response to selection nor the ultimate limits to selection, the nature of correlated responses to selection, nor the nature of gene segregation underlying the observed variability. 9. Strains set up from single inseminated founder females from the same population of Drosophila have been shown to differ genetically for several quantitative traits. Therefore the base population is polymorphic for genes controlling these traits. This was exploited by carrying out directional selection on lines derived from those strains showing a high incidence of scutellar chaetae. This led to far more rapid responses to selection than lines derived from strains where the incidence of scutellar chaetae was lower. 10. Ultimately, one can envisage the selection experiment as it is known today being partly replaced by the manipulation of located genes controlling quantitative traits into certain combinations.     

The changing status of the Brown hare (Lepus capensis L.) in Britain

Game bag records are used to examine temporal and geographical changes in numbers of Brown hares. Records are taken from a survey made by the Oxford Bureau of Animal Population in 1938, which covered over 400 estates, and from the Game Conservancy's National Game Census, which has been monitoring shooting records of between 400 and 500 estates since 1961. Eastern regions of Britain had higher bags of hares than western regions in the three periods; 1891–1910, 1917–1936, 1961–1978. Hare game bags were generally high in counties with large proportions of tilled land. There was no consistent temporal trend in bags from different areas before 1938, but all areas show a considerable reduction in bags since 1961. This reduction is statistically significant. Time-series analysis of one extended set of data did not show evidence of cyclic fluctuations.     

Toxicity of Xanthene Dyes to Entomopathogenic Fungi

Effects of xanthene dyes on mycelial growth and conidial germination in three species of entomopathogenic fungi, Beauveria bassiana, Metarhizium anispoliae and Paecilomyces fumosoroseus, were evaluated in a variety of assay systems. In a disk-diffusion assay, erythrosin B and phloxine B (but not eosin B) produced zones of inhibition in colonies of all three species under continuous exposure to light at disk-loadings of 100mug. None of the dyes produced zones of inhibition in the absence of light at disk loadings of 100mug. Both erythrosin B and phloxine B inhibited mycelial growth of all three species in the light in a dose-dependent manner. Weaker dose-responses for inhibition of growth in the dark were observed for some fungus/dye combinations. Erythrosin B, tested singly, completely inhibited conidial germination in the light in all eight fungal strains tested at 100mug ml-1 medium, but failed to inhibit conidial germination in any of these strains in the dark at the same concentration of dye. For single strains of each of the three fungi, erythrosin B and phloxine B inhibited conidial germination in a dose-dependent manner in the light with IC50s < 6.2mug dye ml-1 medium for all fungus/dye combinations. Phloxine B was a more potent inhibitor of germination than erythrosin B for all three fungal species. At fixed dosages of erythrosin B and phloxine B, inhibition of conidial germination in all three species increased with time of exposure to light. These results constitute the first quantitative demonstration of photodynamic inhibition of conidial germination in fungi by xanthene dyes.     

Cytochromes,Lactic Dehydrogenase and Transformation in Leishmania*

SYNOPSIS. A major difference in heme content was found between leishmanias and leptomonads of Leishmania donovani. When tested with a fluorescence method for heme, leishmanias gave a negative response whereas leptomonads fluoresced brightly. Studies on the terminal respiration of L. tarentolae leptomonads by absorption spectra assay and respiratory inhibitors indicated the presence of cytochromes. Lactic dehydrogenase could not be detected in the leptomonad stage nor could it be found in any other hemoflagellate culture form tested.     

Tobraviruses—plant pathogens and tools for biotechnology

The tobraviruses, Tobacco rattle virus (TRV), Pea early‐browning virus (PEBV) and Pepper ringspot virus (PepRSV), are positive‐strand RNA viruses with rod‐shaped virus particles that are transmitted between plants by trichodorid nematodes. As a group, these viruses infect many plant species, with TRV having the widest host range. Recent studies have begun to dissect the interaction of TRV with potato, currently the most commercially important crop disease caused by any of the tobraviruses. As well as being successful plant pathogens, these viruses have become widely used as vectors for expression in plants of nonviral proteins or, more frequently, as initiators of virus‐induced gene silencing (VIGS). Precisely why tobraviruses should be so effective as VIGS vectors is not known; however, molecular studies of the mode of action of the tobravirus silencing suppressor protein are shedding some light on this process.