Influence of extreme heat or cold stresses on body pigmentation of Drosophila melanogaster.

Thoracic and abdominal pigmentation were measured in Drosophila melanogaster under a cold circadian stress (8-25 °C) and a heat one (18-33 °C) and compared to the phenotypes observed under similar but constant temperatures of 17 or 25 °C respectively. An isofemale line design permitted to submit each line (full sibs) to the four thermal regimes. Under cold stress, the pigmentation was similar to the value observed at constant 25 °C, suggesting a kind of functional dominance of the high temperature phase.

Thermal phenotypic plasticity of body size in Drosophila melanogaster: sexual dimorphism and genetic correlations.

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.

Divergent abdominal bristle patterns in two distantly related drosophilids: antero-posterior variations and sexual dimorphism in a modular trait.

The number of neurosensory bristles on abdominal sternites of Drosophila is a most investigated trait for quantitative genetic studies. However, the developmental pattern expressed on successive segments in both sexes has remained so far a neglected field. We explored three aspects of this general problem with an isofemale line design: comparing two distantly related species, Drosophila melanogaster and Zaprionus indianus, investigating bristle number variation along the antero-posterior axis, and analysing the sexual dimorphism.

Sexual dimorphism of body size and sternopleural bristle number: a comparison of geographic populations of an invasive cosmopolitan drosophilid.

Zaprionus indianus is a cosmopolitan drosophilid, of Afrotropical origin, which has recently colonized South America. The sexual dimorphism (SD) of body size is low, males being almost as big as females. We investigated 10 natural populations, 5 from America and 5 from Africa, using the isofemale line technique.

Sexual size dimorphism in a Drosophila clade, the D. obscura group.

The Drosophila obscura clade consists of about 41 species, of which 20 were used for analyses of wing and thorax length. Our primary goal was to investigate the magnitude of sexual size dimorphism (SSD) of these traits within this clade and to test Rensch's Rule [when females are larger than males, SSD (e.g.

Phenotypic plasticity of body size in a temperate population of Drosophila melanogaster: when the temperature-size rule does not apply.

A natural population of Drosophila melanogaster in southern France was sampled in three different years and 10 isofemale lines were investigated from each sample. Two size-related traits, wing and thorax length, were measured and the wing/thorax ratio was also calculated. Phenotypic plasticity was analysed after development at seven different constant temperatures, ranging from 12 degrees C to 31 degrees C.

Phenotypic plasticity and reaction norms of abdominal bristle number in Drosophila melanogaster.

The phenotypic plasticity of abdominal bristle number (segments 3 and 4 in females) was investigated in 10 isofemale lines from a French population, grown at 7 constant temperatures, ranging from 12 to 31 degrees C. Overall concave reaction norms were obtained with a maximum around 20-21 degrees C. Intraclass correlation (isofemale line heritability) was not affected by temperature.

REML estimates of genetic parameters of sexual dimorphism for wing and thorax length in Drosophila melanogaster.

Restricted maximum likelihood was used to estimate genetic parameters of male and female wing and thorax length in isofemale lines of Drosophila melanogaster, and results compared to estimates obtained earlier with the classical analysis of variance approach. As parents within an isofemale line were unknown, a total of 500 parental pedigrees were simulated and mean estimates computed. Full and half sibs were distinguished, in contrast to usual isofemale studies in which animals were all treated as half sibs and hence heritability was overestimated.

Heat induced male sterility in Drosophila melanogaster: adaptive genetic variations among geographic populations and role of the Y chromosome.

We analyzed genetic variation among geographically diverse populations of Drosophila and showed that tropical flies are more tolerant than temperate ones to heat-induced male sterility, as assessed by the presence of both motile sperm and progeny production. In tropical populations, the temperature inducing 50% sterility (median threshold) is 1 degrees C above the value for temperate populations (30.4 vs.

Genetic variability of sexual size dimorphism in a natural population of Drosophila melanogaster: an isofemale-line approach.

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.

Comparative life histories and ecophysiology of Drosophila melanogaster and D. simulans.

Numerous laboratory investigations have compared Drosophila melanogaster and D. simulans for various life history traits and fitness related ecophysiological parameters. From presently available information, it is however difficult to get a general comparative pattern describing the divergence of their ecological niches and understanding their demographic success.

Male sterility thermal thresholds in Drosophila: D. simulans appears more cold-adapted than its sibling D. melanogaster.

Numerous different criteria may be used for analysing species thermal adaptation. We compared male sterility thresholds in the two most investigated cosmopolitan siblings, D. melanogaster and D.

DESCRIBING THE EVOLUTION OF REACTION NORM SHAPE: BODY PIGMENTATION IN DROSOPHILA.

If phenotypic plasticity is a trait subject to selection and evolution, we need to quantify reaction norms and to identify the potential target(s) of selection. Previously we proposed the use of polynomial coefficients as reaction norm descriptors. However, the interpretation of these coefficients is not straightforward if the reaction norm is not linear.

DESICCATION AND STARVATION TOLERANCE OF ADULT DROSOPHILA: OPPOSITE LATITUDINAL CLINES IN NATURAL POPULATIONS OF THREE DIFFERENT SPECIES.

Desiccation and starvation tolerance were measured along latitudinal transects in three Drosophilid species (Drosophila ananassae, D. melanogaster, and Zaprionus indianus) of the Indian subcontinent. In each case, significant latitudinal clines were observed; desiccation tolerance increased with latitude while starvation tolerance decreased.

GROWTH TEMPERATURE AND ADULT PIGMENTATION IN TWO DROSOPHILA SIBLING SPECIES: AN ADAPTIVE CONVERGENCE OF REACTION NORMS IN SYMPATRIC POPULATIONS?

Phenotypic plasticity of abdomen pigmentation was investigated in populations of the sibling species Drosophila melanogaster and D. simulans, living in sympatry in two French localities. Ten isofemale lines of each population and species were grown at different constant temperatures spanning their complete thermal range from 12 to 31°C.