Chromosoma (Berl.) 81, 199-212 (1980) CHROMOSOMA 9 by Springer-Verlag 1980 Polyploidy in the Australian Leptodactylid Frog Genus Neobatrachus M.J. Mahony and E.S. Robinson School of Biological Sciences, Macquarie University,North Ryde, New South Wales 2113, Australia Abstract. Karyotypic analysis of six species of the Australian leptodactylid frog genus Neobatrachus showed that N. pictus, N. centralis, N. pelobatoides and N. wilsmorei are diploid (2n = 24) while N. sudelli and N. sutor are tetra- ploid (4n =48). Polyploidy has not been reported previously among Austra- lian anurans. Idiograms of the six species indicate that they are similar to the other Australian leptodactylids so thr discribed. DNA values of the tetraploids are approximately double the values for diploids. Tetraploid nu- clear and cell sizes are greater compared with diploids but total body size shows no increase. At diakinesis in primary spermatocytes of tetraploids, mainly tctravalents together with a few bivalents are present. Silver staining of metaphase spreads clearly demonstrates the location of NORs at the secondary constrictions and their frequent association in the tetraploid N. su- tor. Nucleolar number in interphasc nuclei provides a reliable guide for distinguishing tetraploid from diploid frogs in the absence of chromosome analysis and can be determined for both living and preserved specimens. The possible origins and relationships of the tetraploid species are discussed. Introduction Australian ground-dwelling frogs have long been included with their South American relatives in the large family Leptodactylidae. The Australian represen- tatives (subfamily Myobatrachinae) are karyotypically homogeneous and well- defined compared with other leptodactylid groups (Morescalchi, 1973, 1979). Chromosome complemcnts of species from ten Australian genera consist of six relatively long and sic medium to small pairs of metacentrics or submetaccn- trics so that 2n=24, NF=48; those of Platyplectron have one less pair of smaller chromosomes i.e. 2n=22; NF=44 (Robinson and Stephcnson, 1967; Ullerich, 1967; Woodruff, 1972; Morescalchi and Ingram, 1974, 1978; Morescalchi, 1979; King et al., 1979). Six of the 13 documented examples of naturally-occuring anuran polyploidy 0009-5915/80/0081/0199/$02.80