Discovery of new rearrangements for the third chromosome in Colombian Drosophila pseudoobscura populations and homogeneity of rearrangement frequencies through a whole year

The present work is an analysis of the third chromosomal rearrangements, during a year (1996-1997), in several Andean Colombian Drosophila pseudoobscura populations. The two main results obtained were as follows: (1) Several new rearrangements, not reported until now, were detected in these Colombian populations. These new rearrangements were Standard (ST), Cuernavaca (CU), Olympic (OL), and one rearrangement very similar to the Mexican endemic Amecaineca (AM). This discovery puts in evidence that the Colombian D. pseudoobscura karyotype pool is richer than that previously found by other authors. Until now, only the SC (Santa Cruz) and TL (Tree Line) rearrangements had been described in Colombian populations. (2) Another interesting feature discovered in these Neotropical D. pseudoobscura populations was the homogeneity and constancy of rearrangement frequencies throught a year, independently of rain level changes. This result shows that in Colombia there are populations with a rigid polymorphic system, which are typical of central and rich ecological situations, despite of its marginal ecological situation. Only in the Yosemite region of USA a population with the same characteristics has been previously detected. Therefore, the current Colombian Drosophila pseudoobscura populations have a unique chromosomal dynamic.