Latitudinal variation in octanol dehydrogenase and acid phosphatase allele frequencies in Drosophila melanogaster

Summary The octanol dehydrogenase (Odh) and acid phosphatase (Acph) loci of Drosophila melanogaster are each polymorphic for two electrophoretically detectable alleles. The frequencies of the Odh and Acph alleles have been analysed in populations sampled from up to a 40 ° latitudinal range in each of Australasia, North America and Europe/Asia. Odh ^S frequency is found to be significantly negatively associated with distance from the equator in all three zones. The relationship of Acph ^S frequency to distance from the equator is significant and negative in Australasia but neither significant nor consistent in sign in North America and Europe/Asia.     

Latitudinal variability of Drosophila melanogaster: allozyme frequencies divergence between European and Afrotropical populations

Allelic frequencies at five polymorphic loci were determined in seven European and six Afrotropical populations of Drosophila melanogaster. African populations, which may be considered as ancestral for the species, showed a greater genetic diversity as measured by the number of alleles found. Within each geographic group (Europe or tropical Africa) genetic distances between local populations were very small (D = 0.027). By contrast, the average distance between European and African populations (D = 0.389) was more than 12 times bigger. It was previously known that various morphological or physiological differences, which probably reflect genetic adaptations to different environments, exist between these temperate and tropical populations. Data presented here suggest that the divergence in allozyme frequencies also reflects some selective mechanisms.     

Latitudinal variability of Drosophila melanogaster: Allozyme frequencies divergence between European and Afrotropical populations

Allelic frequencies at five polymorphic loci were determined in seven European and six Afrotropical populations of Drosophila melanogaster. African populations, which may be considered as ancestral for the species, showed a greater genetic diversity as measured by the number of alleles found. Within each geographic group (Europe or tropical Africa) genetic distances between local populations were very small (D=0.027). By contrast, the average distance between European and African populations (D=0.389) was more than 12 times bigger. It was previously known that various morphological or physiological differences, which probably reflect genetic adaptations to different environments, exist between these temperate and tropical populations. Data presented here suggest that the divergence in allozyme frequencies also reflects some selective mechanisms.     

Mutagenic effects of thioacetamide in Drosophila melanogaster

Thioacetamide, which is carcinogenic in mice and rats, has been reported as negative in Ames's test on Salmonella his⁻ with and without liver microsomal fraction (S 9 mix). Tests on Drosophila reported here showed a significant increase in sex-linked recessive lethals after treatment with thioacetamide, both after injection and after feeding of males.     

Sterilizing effects of trimethylphosphate in Drosophila melanogaster

Trimethylphosphate (TMP) causes aspermia in D. melanogaster males. If larvae are allowed to develop on standard maize-meal medium containing 0.002 M TMP or greater, the enclosing adult males, when placed on uncontaminated medium, exhibit a period of temporary sterility. Between test groups the period of sterility is most variable at the doses of 0.002-0.004 M, but at 0.005 M or greater is approximately 11-12 days. Near-lethal doses of about 20 g/kg by abdominal injection produces a temporary sterility in adults, whereas oral doses up to 0.02 M are ineffective. Oogenesis in females is not affected by doses which cause temporary sterility in males. In adult male D. melanogaster, which were treated as larvae with 0.01 M TMP in the food medium, the basal region of testes and seminal vesicles do not contain spermatozoa. Cytological examinations of the spermatids reveal ultrastructural changes which are characteristic of those seen in X/O and sterile-mutant males; they contain incomplete axial fibre complexes, abnormal development of the mitochondrial derivatives, and nuclei which fail to elongate and condense. Evidence from cytological studies of larval testes suggests that the chemosterilizing effect of TMP is upon early primary spermatocytes. This is also supported by mating data.     

Fitness effects of Wolbachia and Spiroplasma in Drosophila melanogaster

Maternally inherited endosymbionts that manipulate the reproduction of their insect host are very common. Aside from the reproductive manipulation they produce, the fitness of these symbionts depends in part on the direct impact they have on the female host. Although this parameter has commonly been investigated for single infections, it has much more rarely been established in dual infections. We here establish the direct effect of infection with two different symbionts exhibiting different reproductive manipulation phenotypes, both alone and in combination, in the fruit fly Drosophila melanogaster. This species carries a cytoplasmic incompatibility inducing Wolbachia and a male-killing Spiroplasma, occurring as single or double (co-) infections in natural populations. We assessed direct fitness effects of these bacteria on their host, by comparing larval competitiveness and adult fecundity of uninfected, Wolbachia, Spiroplasma and Wolbachia–Spiroplasma co-infected females. We found no effect of infection status on the fitness of females for both estimates, that is, no evidence of any benefits or costs to either single or co-infection. This leads to the conclusion that both bacteria probably have other sources of benefits to persist in D. melanogaster populations, either by means of their reproductive manipulations (fitness compensation from male death in Spiroplasma infection and cytoplasmic incompatibility in Wolbachia infection) or by positive fitness interactions on other fitness components.     

Wolbachia effects in Drosophila melanogaster: in search of fitness benefits

Insect endosymbionts often influence host nutrition but these effects have not been comprehensively investigated in Wolbachia endosymbionts that are widespread in insects. Using strains of Drosophila melanogaster with the wMel Wolbachia infection, we showed that Wolbachia did not influence adult starvation resistance. Wolbachia also had no effect on larval development time or the size of emerging adults from a low nutrition medium. While Wolbachia may influence the expression of heat shock proteins, we found that there was no effect on adult heat resistance when tested in terms of survival or virility following heat stress. The absence of nutrition or stress effects suggests that other processes maintain wMel frequencies in natural populations of Drosophila melanogaster.     

Cross-generational fitness effects of infection in Drosophila melanogaster

Activation of the immune system is beneficial in defending against pathogens, but may also have costly side effects on an organism's fitness. In this study we examine the fitness consequences of immune challenge in female Drosophila melanogaster by examining both direct (within generation) and indirect (between generations) costs and benefits of immune challenge. Though passing immunity to offspring has been studied in mammals for many years, only recently have researchers found evidence for a cross-generational priming response in invertebrates. By examining both potential fitness costs and benefits in the next generation, we were able to determine what effect immune challenge has on fitness. In agreement with other studies, we found a direct cost to infection, where immune challenged females laid fewer eggs than unchallenged females in two of the three lines we examined. In addition, we found some evidence for indirect costs. Offspring from immune challenged mothers had shorter lifespans than those from unchallenged mothers in two of the three lines. Interestingly, we do not see any effect of maternal immune challenge on offspring's ability to overcome an infection, nor do we see an effect on other fitness traits measured, including egg size, egg-adult viability, and offspring resistance to oxidative stress. While previous studies in bumblebees and beetles have demonstrated cross-generation priming, our results suggest that it may not be a general phenomenon, and more work is needed to determine how widespread it is.     

Mutagenic effects of thioacetamide in Drosophila melanogaster.

Thioacetamide, which is carcinogenic in mice and rats, has been reported as negative in Ames's test on Salmonella his- with and without liver microsomal fraction (S 9 mix). Tests on Drosophila reported here showed a significant increase in sex-linked recessive lethals after treatment with thioacetamide, both after injection and after feeding of males.     

Developmental effects of monensin on Drosophila melanogaster

Extracellular matrix and membrane proteins and their correct secretion probably are key elements in morphogenesis and differentiation in Drosophila. In this study, we have analysed the effects of monensin, a Na⁺-H⁺-ionophore which blocks normal secretion, applied during cellular blastoderm formation on further development. Normal cell morphology and intercellular contacts are lost and the extracellular matrix becomes disorganized. Gastrulation is blocked and abnormal foldings can be observed. Cuticle phenotypes showed different degrees of ventral, dorsal, head and posterior defects. The results are discussed in the context of what is known about membrane and extracellular matrix proteins in Drosophila.     

Mutagen-sensitive mutants in Drosophila melanogaster: effects on premutational damage.

Drosophila melanogaster males from a Basc stock were mutagenized with either X-rays, ethyl methanesulfonate (EMS), or nitrogen mustard (HN2). Groups of identically treated males were crossed to different types of female. Sex-linked recessive lethals were scored as a genetic end point. The females used were homozygous for X-chromosomal mutations (mus(1)101D1, mus(1)104D1, mei-9 or mei-41D5) which lead to defective DNA repair and which increase the mutagen sensitivity of larvae. Females from a white stock with normal DNA repair capacities served as controls. The premutational lesions induced in mature sperm are only processed after insemination by the maternal enzyme systems present in the oocytes. Differences in the efficiency of the processing of lesions can lead to maternal effects on the frequency of mutations recovered from mutagenized sperm. It was found that, with the exception of mus(1)104D1, all mutants analysed significantly modify the mutation fixation of one or more types of premutational lesions. The most drastic effect is found with the mus(1)101D1 stock in which HN2-induced DNA cross-links do not lead to sex-linked recessive lethals. It is assumed that mus(1)101D1 is defective in an early step of DNA cross-link repair. Our first set of data clearly demonstrates that the study of maternal effects in Drosophila is an efficient tool to analyse the in vivo function of repair mutations on chemically induced mutagenesis.