1. During their development in natural conditions, Drosophila larvae and pupae face heterogeneous environmental conditions (HEC). Analysing the morphology of wild-living adults is a means of evaluating the effects of HEC.2. Two drosophilid species of the Zaprionus genus that recently invaded the Nile delta were investigated, and three metric, size-related traits, and one meristic trait, the sternopleural bristle number, were measured. Data were compared with those of F 1 generation reared under favourable laboratory conditions.3. Body size was smaller in nature, but also extremely variable among individuals, with an average coefficient of variation (CV) of 9.1 ± 0.3, against a much lesser value of 2.4 ± 0.1 in laboratory flies. Correlations among size traits were also greater in nature (0.96 ± 0.01) than in the laboratory (0.75 ± 0.04).4. By contrast, sternopleural bristles produced similar results in wild-living and laboratory flies. In nature, mean numbers were only slightly less than in the laboratory and the CVs were almost identical (10.87 ± 0.70 vs 10.80 ± 0.76).5. Fluctuating asymmetry of sternopleural bristles was also identical in the two kinds of flies , and was not influenced by HEC, indicating a high level of developmental canalisation with respect to HEC.6. The implications of the results for the problems of field heritability and developmental stability are discussed.
Zaprionus indianus is an Afrotropical drosophilid species that has expanded its geographical range in the Palearctic region and the Americas during the second half of the last century. It has invaded Egypt within the past two decades from East Africa or Asia and became a dominant species in the drosophilid fauna therein, but the exact date of introduction and source of the propagule remain unknown. Here, we investigate the genetic structure of eight geographical populations within and around the Nile Delta using mitochondrial DNA sequences of the cox2 gene and chromosomal inversion polymorphism. A very low level of genetic variability was detected for both markers, mainly attributed to the introduction bottleneck. Nonetheless, both indicate a significant population structure, with a southeastern-northwestern cline. Demographic history analysis suggested northwestern populations to be younger (expanding in ca. 1992) than southeastern ones (expanding in ca. 1985). The In(II)A polymorphism was only observed in the northwestern population, but one-year interval analysis of the Alexandria population revealed the lack of seasonal fluctuation and a trend toward the loss of the polymorphism. Based on these data and faunistic records, we propose a multiple introduction scenario for Z. indianus in Egypt-according to which a first wave in the early 1980s from Sudan through normal northward range expansion or fruit trade, and a second wave in the early 1990s from Asia via fruit trade. We also suggest, from ecological observations, fruit trade data and known adaptive versatility of Z. indianus, date palm, the dominant fruit in Egypt and in the oases where Z. indianus predominates, to play a major role in the spread of the species in the Middle East.
The present study was undertaken to investigate the genetic nature of zinc (Zn) accumulation in the ear-leaves of maize (Zea mays L.) plants.Fourteen inbred lines were evaluated. Out of which, five inbreds were chosen, two high Zn accumulators (Rg-5 and Rd-2), two low Zn accumulators (Rg-8 and G-307) and a moderate one (K-64). These five parental inbreds were utilized to obtain all possible ten F1 hybrids (in one direction), 10 F2, 10 Bl, and 10 B2. All genotypes were planted and Zn was estimated at 50% tasseling stage. Zinc accumulation in the present genotypes was found to be genetically controlled and affected by additive genes. Significant values were obtained for the General Combining Abilities (GCA) but not for the Specific Combining Abilities (SCA) and the high Zn accumulating parents were the best general combiners. Four genes were found to be the minimum segregating factors in the (high x low) crosses for Zn accumulation.
Mesosternal (MS) bristles in Drosophila are a pair of machrochaetae found at the sternal end of the sternopleural (STP) microchaetae, and are thought to be invariable. In a closely related drosophilid genus, Zaprionus, their number is four and, in contrast to Drosophila, they show interspecific and intraspecific variability. The genetic basis of MS bristle number variability was studied in Z. indianus, the only cosmopolitan species of the genus. The trait responded rapidly to selection and two lines were obtained, one lacking any bristles (0-0) and the other bearing the normal phenotype (2-2). Other symmetrical phenotypes, (1-1) and (3-3), could also be selected for, but with lesser success. By contrast, STP bristle number did not vary significantly between the two lines (0-0) and (2-2), revealing its genetic independence from MS bristle number. Reciprocal crosses between these two lines showed that MS bristle number is mainly influenced by a major gene on the X chromosome (i.e. F(1) males always resembled their mothers) with codominant expression (i.e. heterozygous F(1) females harboured an average phenotype of 2 bristles). However, trait penetrance was incomplete and backcrosses revealed that this variability was partly due to genetic modifiers, most likely autosomal. The canalization of MS bristle number was investigated under different temperatures, and the increased appearance of abnormal phenotypes mainly occurred at extreme temperatures. There was a bias, however, towards bristle loss, as shown by a liability (developmental map) analysis. Finally, when ancestral and introduced populations were compared, the latter were far less stable, suggesting that genetic bottlenecks may perturb the MS bristle number canalization system. MS bristle number, thus, appears to be an excellent model for investigating developmental canalization at both the quantitative and the molecular level.
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