Jean R. David
Articles written in Journal of Genetics
Volume 77 Issue 1 April 1998 pp 13-20
We analysed reaction norms of pigmentation (thorax and abdomen) according to growth temperature for 20 isofemale lines collected near Delhi (India) and compared them to results obtained for two French populations. The climatic conditions of the two locations were strongly different, with monthly average temperature ranging between 4.2°C and 20.5°C in France and between 14.3°C and 34.3°C in India. For each segment, a decrease of the pigmentation was observed with increasing temperature and the shapes of the reaction norms were more or less parallel. On average Indian flies were lighter than French ones, in agreement with the thermal budget hypothesis. We further investigated the shapes of reaction norms by polynomial adjustment and observed significant differences. In several cases, a maximum divergence was observed at high temperature, implying a change in the shape of the norm. Characteristic values related to the thermal reactivity were also significantly different between populations but no general tendency was found. Genetic variability, estimated by the coefficient of intraclass correlation, was significantly lower in India (0.27 ±0.026) than in France (0.39 ±0.028), and we discuss the significance of this difference.
Volume 82 Issue 3 December 2003 pp 79-88
Most animal species exhibit sexual size dimorphism (SSD). SSD is a trait difficult to quantify for genetical purposes since it must be simultaneously measured on two kinds of individuals, and it is generally expressed either as a difference or as a ratio between sexes. Here we ask two related questions: What is the best way to describe SSD, and is it possible to conveniently demonstrate its genetic variability in a natural population? We show that a simple experimental design, the isofemale-line technique (full-sib families), may provide an estimate of genetic variability, using the coefficient of intraclass correlation. We consider two SSD indices, the female-male difference and the female/male ratio. For two size-related traits, wing and thorax length, we found that both SSD indices were normally distributed. Within each family, the variability of SSD was estimated by considering individual values in one sex (the female) with respect to the mean value in the other sex (the male). In a homogeneous sample of 30 lines of
Volume 85 Issue 1 April 2006 pp 9-23 Research Article
A natural population of
Volume 86 Issue 2 August 2007 pp 149-158 Research Article
Mesosternal (MS) bristles in
Volume 87 Issue 3 December 2008 pp 209-217 Research Article
The phenotypic plasticity of wing size and wing shape of
Volume 87 Issue 4 December 2008 pp 407-419 Research Article
Environmental stress has been suggested to be a major evolutionary force, both through inducing strong selection and because of its direct impact on developmental buffering processes that alter the evolvability of organisms. In particular, temperature has attracted much attention because of its importance as an ecological feature and the relative ease with which it can be experimentally manipulated in the lab. Evolution Canyon, Lower Nahal Oren, Israel, is a well studied natural site where ecological parameters are suspected to drive evolutionary differentiation. In this study, using Drosophila melanogaster isofemale lines derived from wild flies collected on both slopes of the canyon, we investigated the effect of developmental temperature upon the different components of phenotypic variation of a complex trait: the wing. Combining geometric and traditional morphometrics, we find only limited evidence for a differentiation among slopes. Investigating simultaneously phenotypic plasticity, genetic variation among isofemale lines, variation among individuals and fluctuating asymmetry, we could not identify a consistent effect of the stressful conditions encountered on the south facing slope. The prevailing structuring effect is that of the experimentally manipulated temperature which clearly influences wing mean size and shape. Variability, in contrast, is not consistently affected by temperature. Finally, we investigated the specific relationship between individual variation and fluctuating asymmetry. Using metric multi-dimensional scaling we show that the related patterns of wing shape variation are not identical, supporting the view that the underlying developmental processes are to a certain extent different.
Volume 90 Issue 2 August 2011 pp 295-302 Research Article
Thirty isofemale lines collected in three different years from the same wild French population were grown at seven different temperatures (12–31°C). Two linear measures, wing and thorax length, were taken on 10 females and 10 males of each line at each temperature, also enabling the calculation of the wing/thorax (W/T) ratio, a shape index related to wing loading. Genetic correlations were calculated using family means. The W–T correlation was independent of temperature and on average, 0.75. For each line, characteristic values of the temperature reaction norm were calculated, i.e. maximum value, temperature of maximum value and curvature. Significant negative correlations were found between curvature and maximum value or temperature of maximum value. Sexual dimorphism was analysed by considering either the correlation between sexes or the female/male ratio. Female–male correlation was on average 0.75 at the within line, within temperature level but increased up to 0.90 when all temperatures were averaged for each line. The female/male ratio was genetically variable among lines but without any temperature effect. For the female/male ratio, heritability (intraclass correlation) was about 0.20 and evolvability (genetic coefficient of variation) close to 1. Although significant, these values are much less than for the traits themselves. Phenotypic plasticity of sexual dimorphism revealed very similar reaction norms for wing and thorax length, i.e. a monotonically increasing sigmoid curve from about 1.11 up to 1.17. This shows that the males are more sensitive to a thermal increase than females. In contrast, the W/T ratio was almost identical in both sexes, with only a very slight temperature effect.
Volume 99, 2020
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