Heteromorphic sex chromosomes inEupsophus insularis (Amphibia: Anura: Leptodactylidae)

The chromosomes of the Chilean frogEupsophus insularis are described for the first time. This species has a chromosome number of 2n=30, and based on the karyotype it is concluded thatE. insularis is closely related toE. migueli. E. insularis has an XX/XY system of sex determination, and pericentromeric constitutive heterochromatin is present in all chromosomes except in the Y chromosome. It is postulated that the Y chromosome is derived from a small ancestral metacentric chromosome that lost its heterochromatic segment.accepted for publication by M. Schmid