Summary
An electrophoretic study was undertaken to determine the extent of genetic variability in three taxa of legumes (Aeschynomene sensitiva Sw. var. sensitiva, Aeschynomene sensitiva Sw. var. amazonica Rudd, Papilionoideae: Mimosa pigra L , Mimosoideae) along a 2,174 Km reach of the Amazon River from Iquitos, Peru, to Manaus, Brazil. Genetic variability was expressed in terms of: 1) degree of enzyme polymorphism (P'), and 2) average populational heterozygosity (H'). Five enzyme systems were examined: leucine aminopeptidase (LAP), glutamate dehydrogenase (GDH), phosphoglucomutase (PGM), phosphoglucoisomerase (PGI). and acid phosphotase (AcPH). Riverine taxa provide a unique system for the experimental study of population biology and evolution. The origin, perpetuation, and dynamics of genic variation within and among populations is used as an indicator of evolutionary change. Gene flow in these entomophilous, water dispersed legumes is undirectional and linear, with minor blackflow by pollen vectors. Of the enzymes examined, LAP was a monomer for all three taxa with low polymorphic values. AcPH, also a codominant monomer, had no detectable isoenzyme fraction; a situation also found in PGM systems. PGI is a very complex system controlled by several loci. GDH is monomorphic with one resolvable band. Mean polymorphism for the two Aeschynomene taxa is 21.3% (P' = 0.213), and for the Mimosa is 24.5% (P' = 0.245). Average populational heterozygosity (Nei statistic, H') varied between 0.10 to 0.43 for Aeschynomene. This value was significantly higher for the Mimosa, which ranged between 0.33 and 0.50. Heterozygosity index, genetic similarity index, demographic patterns, and biology show a concise correlation between genetic variability and adaptative strategy. Populations with a high extinction probability are more homozygous than populations with greater survival probability. Homozygosity is favored in perturbed populations along the Rio Amazonas.