LONG-TERM CHANGES AND SEASONAL FLUCTUATIONS IN THE CHROMOSOMAL-POLYMORPHISM OF CHILEAN POPULATIONS OF DROSOPHILA-IMMIGRANS

Chilean populations of Drosophila immigrans are polymorphic for three paracentric inversions in the second chromosome designated as A, B and C. The other chromosomes are homosequential. In the last 35 years, substantial changes have been detected in the distribution or frequencies of two of the inversions. Inversion C, originally restricted to a local area near Valdivia (Lat. 39-degrees 41'S) in the 1950'S, has extended its distribution over the country from Lat. 29-degrees-54'S to Lat. 41-degrees-28'S. Inversion B, the only inversion present in all the populations examined, exhibits significant seasonal fluctuations in frequency. Inversion A, present in the Central and Southern regions of Chile, shows neither changes in seasonal frequencies nor in its distribution in Chile. It can be concluded that microevolutionary changes in D. immigrans, and probably in other species of the genus, are faster than formerly postulated.