Genetic and morphometric analysis of three species of the genus HypostomusLacepede, 1803 (Osteichthyes : Loricariidae) from the Rio Iguacu basin (Brazil)

Three species of Hypostomus from the Rio Iguacu basin, H. aff. commersonii, H. derbyi and H. myersi, were examinated by multivariate analysis, PCA and size-free discriminant canonical analysis, by the external characters trus s network method and starch gel isoenzyme electrophoresis in heart, liver a nd muscle tissues. Twenty-six gene loci of 14 isoenzyme systems (AAT, ACP, ADH, GDH, G3PDH, G6PDH, GPI, IDHP, LDH, MDH, ME, PGM, PER and SOD) were sco red for the first time for these species. The percentage of polymorphic loc i (P0.99) varied from 11.54% for H. derbyi and H. myersi to 19.23% in H. af f. commersonii. Expected mean heterozygosity (H-e) varied from 0.011 in H. derbyi to 0.044 in H. aff. commersonii. Nei's genetic distance (D) between H. aff. commersonii and H. derbyi was 0.142, between H. aff. commersonii an d H. myersi 0.621, and between H. derbyi and H. myersi 0.776. We discuss hy potheses for the maintenance of the low mean heterozygosity observed, and f or the presence of these species in this drainage basin.