E. C. R. Reeve

Bio: E. C. R. Reeve is an academic researcher. The author has an hindex of 1, co-authored 1 publications receiving 164 citations.

Some genetic tests on asymmetry of sternopleural chaeta number in Drosophila

Abstract: 1. Published data suggest that mean left-right asymmetry in number of sternopleural bristles of D. melanogaster declines when inbred lines are crossed, while the corresponding variance for sternite bristles remains unchanged. Some genetic tests were undertaken to analyse this difference in behaviour of the two characters.2. A progeny test on a wild stock showed that a small amount of genetic variance in sternopleural asymmetry was present, equivalent to about 2% of the total phenotypic variance.3. It was possible to increase and decrease the level of sternopleural asymmetry in two wild stocks by selection. These experiments gave an estimated heritability of some 2–3%, in close agreement with the progeny test. Change in asymmetry did not necessarily lead to a change in mean count.4. Homozygous lines, consisting of individual third chromosomes from the Renfrew wild stock made homozygous in an inbred line genetic background, were intercrossed, and the average indices for a number of characters of eight inter crosses involving eight lines were compared with their mid-parent averages. Thorax length was 2% greater and its variance 32% less in the crosses; total sternopleural count and its variance did not change significantly, but the asymmetry variance declined by 18%. In contrast, the corresponding asymmetry or independent variance for numbers of sternite bristles was 6% higher in the crosses, although the total sternite count and its variance did not change. These results fit in with previous work.5. Tests on a similar set of homozygous lines in which the third chromosomes came from the SP wild stock, and on some long inbred lines from the Pacific wild stock, gave discordant results. Of eight SP lines examined, four were homozygous for a gene polychaetoid, and four were homozygous for a genetic effect causing sockets without bristles to occur among the sternopleurals. Both types had much greater sternopleural variance and asymmetry than the Renfrew lines, and both indices declined sharply in intercrosses leaving these genetic effects heterozygous, but neither declined if they were left homozygous in the crosses. Similarly high sternopleural variances were found in the Pacific lines, but only the total variance declined in males and only the asymmetry variance declined in the females, when they were intercrossed. All the four Pacific lines tested appeared to be homozygous for a genetic effect which caused a variable number of dorso-central and scutellar bristles to be replaced by sockets without bristles, and an occasional extra scutellar bristle to appear. This effect was also probably responsible for the high sternopleural variances.6. Males of the Pacific inbred lines and intercrosses were compared when reared on the normal live medium and on a synthetic diet in reduced concentration, which reduced body-size by 23% (thorax area). The inbred lines were reduced more than the F1's in total sternopleural count and its variance, but the F1's were reduced more in sternopleural asymmetry, by the restricted diet.7. The problems of interpreting these experiments, in view of our ignorance of the biological functions and attributes of the sternopleural and sternite bristles, are discussed. It is concluded that we have no basis yet for deciding whether sternopleural bristle number is of adaptive significance, but this is considered improbable.8. The experimental evidence suggests that sternopleural asymmetry cannot be considered a measure of general developmental stability, particularly as the level of asymmetry can be reduced by selection well below that of typical wild stocks.9. The scaling problems arising when the mean asymmetry of lines with different mean counts are to be compared, are examined, and it is suggested that the ratio of asymmetry to total count does not eliminate scale effects.10. Developmental and anatomical differences between the sternopleural and sternite bristles suggest a possible reason why they behave differently when inbred lines are intercrossed.

Evolutionary Significance of Phenotypic Plasticity in Plants

Abstract: Publisher Summary This chapter focuses on evolutionary significance of phenotypic plasticity in plants. The expression of an individual genotype is modified by its environment. The amount by which it can be modified is termed its plasticity. This plasticity can be either morphological or physiological; these are interrelated. The plasticity of a character is related to the general pattern of its development, and apart from this, that plasticity is a general property of the whole genotype. Plasticity of a character appears to be specific for that character, specific in relation to particular environmental influences, specific in direction, under genetic control not necessarily related to heterozygosity, and able to be radically altered by selection. Because plants are static organisms, plasticity is of marked adaptive value in a great number of situations. Examples of all these situations in plant species are discussed. They indicate that adaptation by plasticity is a widespread and important phenomenon in plants and has evolved differently in different species. The mechanisms involved in plasticity are varied. At one extreme, the character shows a continuous range of modification dependent on the intensity of the environmental stimulus. At the other, the character shows only two discrete modifications. The stimulus causing these modifications may be direct or indirect. The mechanisms found can be related to the particular environmental situation involved.

Fluctuating Asymmetry: Measurement, Analysis, Patterns

Abstract: With these words Darwin opened a brief paragraph citing observations antithetical to his supposition: anecdotal reports of the inheritance of characters missing from one side of the body. His initial hunch, however, has stood the test of time: Genetic studies have confirmed that where only small, random deviations from bilateral symmetry exist, the deviations in a particular direction have little or no measurable heritability (17, 47, 51, 65a, 73a, 74, 91). The genetic basis of bilateral symmetry thus appears to differ fundamentally from that of virtually all other morphological features. Why, then, all the recent (and not so recent) interest in such minor, nondirectional deviations from bilateral symmetry [fluctuating asymmetry (FA); 60 cited in 99]? Four reasons. First, FA relates in a curious way to what is perhaps the major unsolved general problem in modem biology: the orderly expression of genotypes as complex, three-dimensional phenotypes. As was emphasized in a flurry of activity in the mid to late 1950s, and many times since, FA provides an appealing measure of 'developmental noise,' or minor environmentally induced departures from some ideal developmental program (101). Its appeal derives from an a priori knowledge of the ideal: perfect bilateral symmetry. For unilateral characters, the ideal is rarely known (but see 1, 2, and 59 for one possible approach). A second reason for interest in

A study of fluctuating asymmetry

Abstract: Fluctuating asymmetry, discussed below, is commonly used to estimate the effects of minor developmental accidents. These accidents differ between individuals, and there are also individual differences in resistance to these accidents. The ability to resist such developmental accidents will here be referred to as buffering against them. Because of the interrelations of morphogenetic systems, it is possible that an organism well buffered in one character is also well buffered in others, i.e., for this reason the microenvironmental perturbations on different systems in an individual may result in a tendency for the fluctuating asymmetry of different characters in that individual to be higher or lower than usual. Such a correlation in buffering capacities could also-be produced by differences in genotypes and environments acting separately'on different morphogenetic systems, but this is another matter. This investigation concerns the fluctuating asymmetry of different characters. No new evidence is given as to buffering against environmental stresses of a larger scale, such as temperature or the presence of parasites. A mean positive correlation between the fluctuating asymmetries of a number of un-

Fluctuating asymmetry: an epigenetic measure of stress

Abstract: (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.

Mapping phenotypes: canalization, plasticity and developmental stability

Abstract: The relationship between genotype and phenotype is not one to one. This statement is central to our understanding of how natural selection shapes phenotypic evolution. Here, we clarify the links between canalization, plasticity and developmental stability, the three major processes involved in the control of phenotypic variability. We present a short historical review, including the original definitions of these concepts, and then summarize their current meaning and use, highlighting possible sources of confusion. Some of the perspectives allowed by a more synthetic conceptual framework are presented, in the light of the recent advances in molecular and developmental genetics.