Phenotypic variability of wild living and laboratory grown Drosophila: Consequences of nutritional and thermal heterogeneity in growth conditions

Catalogue of the Diptera (Insecta) of Morocco- an annotated checklist, with distributions and a bibliography

The faunistic knowledge of the Diptera of Morocco recorded from 1787 to 2021 is summarized and updated in this first catalogue of Moroccan Diptera species. A total of 3057 species, classified into 948 genera and 93 families (21 Nematocera and 72 Brachycera), are listed. Taxa (superfamily, family, genus and species) have been updated according to current interpretations, based on reviews in the literature, the expertise of authors and contributors, and recently conducted fieldwork. Data to compile this catalogue were primarily gathered from the literature. In total, 1225 references were consulted and some information was also obtained from online databases. Each family was reviewed and the checklist updated by the respective taxon expert(s), including the number of species that can be expected for that family in Morocco. For each valid species, synonyms known to have been used for published records from Morocco are listed under the currently accepted name. Where available, distribution within Morocco is also included. One new combination is proposed: Assuaniamelanoleuca (Séguy, 1941), comb. nov. (Chloropidae).

The roles of cell size and cell number in determining ovariole number in Drosophila

All insect ovaries are composed of functional units called ovarioles, which contain sequentially developing egg chambers. The number of ovarioles varies between and within species. Ovariole number is an important determinant of fecundity and thus affects individual fitness. Although Drosophila oogenesis has been intensively studied, the genetic and cellular basis for determination of ovariole number remains unknown. Ovariole formation begins during larval development with the morphogenesis of terminal filament cells (TFCs) into stacks called terminal filaments (TFs). We induced changes in ovariole number in Drosophila melanogaster by genetically altering cell size and cell number in the TFC population, and analyzed TF morphogenesis in these ovaries to understand the cellular basis for the changes in ovariole number. Increasing TFC size contributed to higher ovariole number by increasing TF number. Similarly, increasing total TFC number led to higher ovariole number via an increase in TF number. By analyzing ovarian morphogenesis in another Drosophila species we showed that TFC number regulation is a target of evolutionary change that affects ovariole number. In contrast, temperature-dependent plasticity in ovariole number was due to changes in cell-cell sorting during TF morphogenesis, rather than changes in cell size or cell number. We have thus identified two distinct developmental processes that regulate ovariole number: establishment of total TFC number, and TFC sorting during TF morphogenesis. Our data suggest that the genetic changes underlying species-specific ovariole number may alter the total number of TFCs available to contribute to TF formation. This work provides for the first time specific and quantitative developmental tools to investigate the evolution of a highly conserved reproductive structure.

Phenotypic variability of natural populations of an invasive drosophilid, Zaprionus indianus, on different continents: comparison of wild-living and laboratory-grown flies

Phenotypic variability in nature is the most important feature for Darwinian adaptation, yet it has been rarely investigated in invasive species. Zaprionus indianus is an Afrotropical drosophilid species that have recently invaded the Palearctic and the Neotropical regions. Here, we compared the variability of three size-related traits and one meristic trait the sternopleural (STP) bristle number, between wild-collected flies living under different conditions: a stressful Mediterranean environment in Egypt, and a benign tropical environment in Brazil. From each population, a F(1) generation was also grown under the stable conditions of the laboratory. Variability of size in nature had a variance 13 times greater than in the laboratory, but not affected by different climates. By contrast, STP variability was identical in nature and in the laboratory. Sexual dimorphism was also investigated with contrasting results between traits. It is suggested that the very high invasiveness of Z. indianus might be related to a better capacity to survive adverse conditions.

Quantitative morphometrical analysis of a North African population of Drosophila melanogaster: sexual dimorphism, and comparison with European populations

Genetic variability of quantitative traits was investigated in a Moroccan population of Drosophila melanogaster, with an isofemale line design. Results were compared with data previously obtained from French populations. Although the environmental and thermal conditions are very different in France and Morocco, only two significant differences were observed: a shorter wing and a lighter abdomen pigmentation in Morocco. It is, therefore, concluded that Moroccan D. melanogaster are quite typical temperate flies, belonging to the Palaearctic region, and very different from the ancestral Afrotropical populations. Almost all traits were genetically variable, as shown by significant intraclass correlations among lines. Genetic correlations were highly significant among three size-related traits, while much lower between size and bristle numbers. Fluctuating asymmetry was greater for abdominal bristles than for sternopleural bristles. Sex dimorphism, analysed as a female/male ratio, was identical in French and Moroccan populations. Examination of the thorax length/thorax width ratio showed that the thorax is more elongated in females. Sexual dimorphism of wing length was significantly more correlated to thorax width than to thorax length. The results illustrate the value of measuring numerous quantitative traits on the same flies for characterizing the genetic architecture of a natural population. In several cases, and especially for genetic correlations, some interesting suggestions could be made, which should be confirmed, or invalidated, by more extensive investigations.

Short-term hardening effects on survival of acute and chronic cold exposure by Drosophila melanogaster larvae

We quantified the variation and plasticity in cold tolerance among four larval stages of four laboratory strains of Drosophila melanogaster in response to both acute (<2h of cold exposure) and chronic ( approximately 7h of cold exposure) cold exposure. We observed significant differences in basal cold tolerance between the strains and among larval stages. Early larval instars were generally more tolerant of acute cold exposures than third-instar larvae. However, wandering larvae were more tolerant of chronic cold exposures than the other stages. Early stages also displayed a more pronounced rapid cold-hardening response than the later stages. Heat pre-treatment did not confer a significant increase in cold tolerance to any of the strains at any stage, pointing to different mechanisms being involved in resolving heat- and cold-elicited damage. However, when heat pre-treatment was combined with rapid cold-hardening as sequential pre-treatments, both positive (heat first) and negative (heat second) effects on cold tolerance were observed. We discuss possible mechanisms underlying cold-hardening and the effects of acute and chronic cold exposures.