No abstract

We evaluated genetic differences between two populations of Drosophila melunoguster that differed in thermal tolerance. Adults of one tropical population (Mali) survived heat shock (39.5"C for 30 min.) at 84%. By contrast, those from a strain collected in Denmark survived at a rate of only 53 'YO. The greatest effect on variation was differences in cytoplasms, but variation in chromosomes 2 and 1 also played a role on tolerance. Heat shock proteins, however, reside on chromosome 3 and, therefore, variation at these sites is low or differences had little effect on results obtained from the methods employed.

An analysis of the interpopulational differences observed between four European and four Chilean stocks of Drosophila subobscura, with regard to wing size, egg-to-adult development time and preadult viability, shows highly significant differences between the eight stocks irrespective of the continent from which the flies are derived. The divergence of the local populations with regard to the quantitative traits described here, supplements other evidence of interpopulational differences in mating activity, chromosomal and enzyme polymorphisms. These together indicate that the evolutionary process that promotes race formation is relatively rapid, bearing in mind that D. subobscura was detected for the first time in South America in 1978.

In February 1978, in Puerto Montt (Chile) the palearctic species Drosophila subobscura was detected. The expansion of the species in this country has been very rapid, and now it is found over a distance of at least 2000 km North-South. The newly established populations are very flourishing and show a high degree of inversion chromosomal polymorphism. On the basis of the chromosomal arrangements present, an hypothesis can be formulated about the origin and characteristics of the founder group. Possibly, the founders came from Eastern or South Eastern Spain and formed a group of 10 or more individuals. The colonization of D. subobscura in Chile seems to follow the model of expansion of a cosmopolitan species, passively transported by man rather than the more active expansion of colonizers less tied to human activity, envisaged in Carson's models of colonization processes. The high level of chromosomal polymorphism observed in the populations of D. subobscura in Chile, coincides with this interpretation.

Monthly collections of Drosophilidae during a three years period, at a small area near Santiago, Chile, were analized by quantitative methods. The diversity analysis, the index of evenness and cluster analysis of the samples and species in time, shows that the community structure changes drastically through the year and, that each species has a clear seasonal pattern. Analyses of the niche breadths for each of the species indicate that the most common species (these are 8 out of the 17 species collected) are all most clear generalists, whereas the remaining 9 species appear rather narrow with regard to seasonality. The analyses of niche overlap revealed that there is a strong tendency for association between certain species. The recently introduced palearctic species D. subobscura tends to be more closely associated to the native species such as D. pavani and the scaptomizids, than to the cosmopolitan species, such as D. simulans and D. melanogaster. Zusammenfassung Analyse einer Drosophila‐Gemeinschaft an einem Standort in Zentral‐Chile über einen Zeitraum von drei Jahren Monatliche Drosophila‐Fänge über einen Zeitraum von drei Jahren an einem Standort bei Santiago in Chile wurden mit quantitativen Methoden analysiert. Die Diversitätsanalyse, der Index für Gleich‐förmigkeit (eveness) und die Clusteranalyse der Stichproben bzw. der Artenzusammensetzung in der Zeit zeigen, daß sich die Struktur des Artenspektrums über das Jahr hinweg drastisch verädert und daß jede Art ein deutliches Jahreszeiten‐Muster hat. Die Analysen über die Nischenbreiten für jede der Arten weisen darauf hin, daß die häufigsten Arten (das sind 8 der 17 gefangenen Arten) in allen Fállen allgemeine Generalisten sind, während die verbleibenden 9 Arten durch ein ziemlich kurzes jahreszeitliches Auftreten gekennzeichnet sind. Die Analysen der Nischenüberlappungen ergeben, daß es eine strenge Tendenz für eine Assoziation zwischen bestimmten Arten gibt. Die est vor kurzem eingeschleppte paläarktische Art D. subobscura tendiert mehr dam, gemeinsam mit den endemischen Arten, wie D. pavani und den Scaptomyciden, hufzutreten als mit den kosmopoliten Arten, wie D. simulans und D. melanogaster.