No abstract

1. D. melanogaster and D. simulans are sibling species; they are morphologically almost identical and genetically very similar. Whereas their sexual behavior patterns are qualitatively similar, hybrids are rarely produced and when they are, they are sterile. 2. Although not all data are in agreement, D. melanogaster generally exhibits more chromosomal, enzyme, and protein polymorphism than does D. simulans. Utilizing this relationship, as well as arguments presented in the literature, one can argue for an association between genetic variability and level of ecological heterogeneity. This association is found for two major environmental variables, temperature and light dependence. 3. On a seasonal basis, D. melanogaster achieves large population numbers early in the summer, as D. simulans does in the autumn...

Monthly collections of three Drosophila species were made over a 39-month period. D, melanogaster was found to be the most common species during summer, D. sirnulans during autumn and D. irnrnigrans during winter. Numerical fluctuations were most marked in the first two species and were related to macroenvironmental temperature. The D. irnmigrans population remained relatively constant throughout the year and the number of the species collected was independent of macroenvironmental variation. For all three species the dimensions of the niche were related to macroenvironmental temperature. This result is discussed in relation to the interaction between numbers in the population, the niche breadth of the species and the environment.

Olfactory response and resource utilization in Drosophila were compared among three domestic ( D . melanogaster, D. simulans, D. immigranr) and one Australian endemic ( D . lafivittata) species. Olfactory response was measured in a choice type olfactometer (Fuyama, 1976). The following chemicals common in Drosophila resources were used as odourants: acetaldehyde, acetic acid, propionic acid, methanol, ethanol, n-propanol, isopropanol, n-butanol. Resource status of these chemicals was determined either from the literature or by adult longevity tests.All species were attracted by acetaldehyde, while methanol, isopropanol and n-butanol were unattractive. Ethanol attracted all species except D . immigrans, while only D . lativittata and D . melanogastcr were attracted to n-propanol, propionic acid and acetic acid Methanol and isopropanol were not utilized as resources by any of the species, while D . melanogaster and D . lativitfata showed greater utilization/tolerance of the other chemicals. Some correlation between resource utilization and olfactory response was found at the interspecific level, although not all chemicals utilized as resources are attractants. The adaptive significance of the interspecific variation in olfactory response is discussed, especially in relation to habitats selected. The results provide suggestions for habitat selection studies at the intraspecific level.

On the basis of life-span, the threshold ranking at which ethanol and acetic acid ceased to be resources and became stresses for 3 sympatric, cosmopolitan Drosophila species was: D. melanogaster Mg. > D. simulans Sturt. > D. immigrans Sturt. The threshold ranking between larval attraction and avoidance followed the same sequence. An Adh-null mutant of D. melanogaster utilised ethanol to an extremely low threshold, while acetic acid was utilised to a threshold close to that of the D. melanogaster population; this predictable result was paralleled by larval attraction to acetic acid but not ethanol. It can therefore be concluded that there is an association between biochemical and behavioural phenotypes relating to resources commonly available in nature. Acetic acid acts as an attractant to larvae of all species at concentrations down to 1/1000 of the concentrations of ethanol attracting flies, which suggests that acetic acid may be a resource recognition compound, as well as a food resource.