THE EVOLUTIONARY HISTORY OF DROSOPHILA-BUZZATII .27. THORAX LENGTH ISPOSITIVELY CORRELATED WITH LONGEVITY IN A NATURAL-POPULATION FROM ARGENTINA

The correlation between body size and longevity was tested in an Argen tinian natural population of Drosophila buzzatii. Mean thorax length o f flies newly emerging from rotting cladodes of Opuntia vulgaris was s ignificantly smaller than that of two samples of flies caught at baits . The present results which might be interpreted as directional select ion for longevity favoring larger flies are in agreement with previous results achieved in a Spanish natural population of D. buzzatii. Flie s emerging from different substrates showed significant differences in thorax length, suggesting that an important fraction of phenotypic va riance can be attributed to environmental variability. However, labora tory and field work in different populations of D. buzzatii showed a s ignificant genetic component for thorax length variation.