Karyotypes of two Australian hylids

Karyotypes of the Australian frogs Hyla caerulea (White) and Hyla phyllochroa Günther were prepared and analysed from colchicine-treated, primary cultures of adult heart, lung and kidney. The diploid chromosome number for both species is 26, which resembles that of most known karyotypes of Papuan hylids but differs from that of the genus Hyla in other regions. A statistical comparison, involving data from arm ratios, centromere indices and relative lengths of metaphase chromosomes of H. caerulea incubated at 31 and 37° C respectively, showed that the differences were non-significant at the 5% level. Similar treatment of data from cells of Hyla caerulea and Hyla phyllochroa incubated at 31°C failed to show a significant species difference. Absolute lengths of haploid chromosome complements of the two species at the same temperature were found to differ significantly. No evidence of sexual heteromorphism was found. The occurrence of a terminally situated, heterochromatic zone associated with the longer arm of the 11th pair of chromosomes is described and compared with the known condition in other hylids.