No abstract

Expression of the amylase multigene family of Drosophila ananassae was investigated in thirdinstar larvae and adults. A developmental differentiation was found between the Amyl-2 and Amy3-4 gene clusters, the former being preferentially expressed in larvae, the latter in adults. During adult life, we observed a decrease in Amy] -2 expression in males of certain strains. We have raised some arguments for the existence of trans-active regulators, acting as repressors of Amy]-2 in adults. The putative repressors might exhibit a geographical polymorphism, with a fixed active form in Pacific regions and a polymorphic pattern in Africa, thus increasing the diversity observed in adult amylase phenotypes. A clear differentiation between the two gene clusters was also found in tissue-specific activity along the third-instar larval midgut. In the anterior midgut, only Amy]-2 is active, while both gene groups are expressed in the posterior midgut, with an additional subzonation within it.

It was shown earlier that variants for the regulatory and structural components of the a-amylase gene-enzyme system in populations of D. melanogaster show moderate to strong linkage disequilibria suggesting selection. Here we demonstrate directly, that there are selective differences between particular combinations of regulatory variants of map genes, controlling a-amylase midgut activity patterns, and structural variants of a-amylase encoded by the Amy genes. Adult survival of stocks homozygous for different combinations of Amy and map variants was measured on carbohydrate solutions of starch, maltose and glucose, respectively. On starch, within Amy1 and Amy4'6 stocks, the map variant with extended a-amylase midgut activity pattern lived longer than the map variant with the small a-amylase midgut activity pattern. However, both Amy4'6 stocks lived longer on starch than the Amy1 stocks. On maltose and glucose no differences were recorded. Differences in survival on starch could be related to a-amylase activity levels. It is concluded that polymorphism of both the regulatory map genes and the structural Amy genes are important for determination of the selective differences between D. melanogaster stocks on starch.

The Drosophila fauna of a deciduous flood plain forest rich in undergrowth near the river Isar, close to Munich, Germany, was surveyed in summer 1990. Decaying herbage baits (decay artificially induced) were set out to study the exploitation of that resource by Drosophila. Sixteen plant species belonging to several families dominant in the collecting area were tested. All attracted and produced drosophilid flies. Ten Drosophila species utilized decaying plant material as breeding sites; at least eight of the ten are polyphagous. Decaying stalks and leaves of Angelica sylvestris (Apiaceae) were examined in detail. In the case of the most frequent species of Drosophila attracted to A. sylvestris, the number of adults collected did not correlate with the number of flies emerging from the substrate. This was particularly true of D. limbata and D. phalerata. When oviposition and larval development of D. limbata and D. phalerata on A. sylvestris was tested in the laboratory, the number of offspring per female was the same in both species. The difference between these two species of the quinaria group in the exploitation of A. sylvestris in the field is therefore not due to differential suitability of the substrate.

Three sibling species of Drosophila, D. melanogaster, D. simulans and D. mauritiana, still without complete reproductive isolation, show specific fluorescent patterns. The difference is so striking that a tubular lamp of 365 nm U.V. light and a binocular are sufficient for routine observations. Besides those differences, it has been concluded from the comparison with totally different species like Drosophila busckii and D. littoralis that the basic pattern formations of the three species are broadly the same. Observations of behaviour under U.V. light suggest that the visual stimulation is integrated in communication in addition to olfactory, aural and tactile stimuli. Our preliminary results suggest that fluorescence is widely present in insects, perhaps even in arthropods in general. Such fluorescent patterns can perhaps shed a new light upon the status of sibling species. The results suggest that fluorescence is dependent on redox-sensitive pteridines.