Heteromorphic Z and W sex chromosomes in Physalaemus ephippifer (Steindachner, 1864) (Anura, Leiuperidae)

Heteromorphisms between sex chromosomes are rarely found in anurans and sex chromosome differentiation is considered to be a set of recent recurrent events in the evolutionary history of this group. This paper describes for the first time heteromorphic sex chromosomes Z and W in the leiuperid genus Physalaemus. They were found in P. ephippifer, a species of the P. cuvieri group, and corresponded to the eighth pair of its karyotype. The W chromosome differed from the Z chromosome by the presence of an additional segment in the short arm, composed of a distal NOR and an adjacent terminal DAPI-positive C-band. The identification of this sex chromosome pair may help in future investigations into the sex determining genes in the genus Physalaemus.