KARYOTYPE PLASTICITY IN NEOTROPICAL LEISHMANIA - AN INDEX FOR MEASURING GENOMIC DISTANCE AMONG L(V)-PERUVIANA AND L(V)-BRAZILIENSIS POPULATIONS

A method for phenetic analysis of karyotype data has been developed fo r Leishmania populations. Measurement of size difference between chrom osomes recognized by a given DNA probe in different isolates led to th e formulation of a Chromosome Size Difference Index (CSDI). The method was applied to phenetic analysis of 4 sets of chromosomes each set be ing recognized by a different probe - in 37 L. (Viannia) peruviana iso lates sampled along a North-South transect through the Peruvian Andes and, in 11 L. (V.) braziliensis isolates from the Amazonian forest (Pe ru, Bolivia and Brazil). Karyotype variability was better accounted fo r by CSDI than by a method based on disjunctive encoding of karyotype data. CSDI evidenced the nature of relationships between L. braziliens is and L. peruviana and it provided a coherent picture of geographical and genomic differentiation among parasite populations. The latter di d cluster according to their geographical origin. L. braziliensis was found karyotypically more homogeneous than L. peruviana. Within L. per uviana, Northern populations were closer to L. braziliensis than to So uthern L. peruviana populations. The validity of karyotypic population s, or karyodemes, was sustained.