Karyotype of a Ranid Frog, Platymantis pelewensis, from Belau, Micronesia, with Comments on Its Systematic Implications

Abstract

The karyotype of Platymantis pelewensis Peters, 1867, the only native, endemic amphibian in Belau, extremely isolated from other congeners, consisted of 2n = 22 homologous chromosomes largely forming a graded series. Of these, chromosomes of pairs 1, 5, 6, 8, 10, and 11 were metacentric; the remainder were submetacentric. Secondary constrictions were evident on shorter arms of pair 7. This karyotype is nearly identical with that of P. papuensis Meyer from New Guinea, but is distinct from two Philippine congeners hitherto karyotyped both in chromosome number and morphology. This suggests that the ancestral form of P. pelewensis dispersed from New Guinea or other Melanesian islands.