CHROMOSOME LINEAGES IN AFRICAN RANOID FROGS

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Abstract
A microcomputer was used to assist with the analysis of chromosomes obtained from 52 species of African ranoid frogs. Although variation in chromosome number and morphology was encountered, the karyotypes provide evidence for two major chromosome groupings derived from an early dichotomy which resulted in two ancestral karyotypes having 26 and 24 chromosomes (2n). Subsequent chromosomal diversification has resulted in a variety of karyotypes with diploid numbers ranging from 14 to 54. The species which may be related to a 26-chromosome ancestral lineage are included in the genera Anhydrophryne, Chiromantis, Hylarana, Petropedetes, Rana, and Tomopterna. All these genera have species which posses a generalized karyotype which exhibits five pairs of distinctively larger chromosomes and a sharp distinction between the large and small chromosome pairs. Astylosternus and Pyxicephalus species may be derived from such a karyotype. Species in the genera Afrixalus, Hemisus, Kassina, Opisthothylax, Phlyctimantis, and Ptychadena may be related to an ancestral 24-chromosome karyotype. Chromosome number variation in Leptopelis, Cardioglossa, and Phrynobatrachus should be useful to outline species groupings within these genera. Twenty-four chromosomes were also found in Callulina kreffti Nieden, a brevicepine microhylid, which has a karyotype which is similar to the ranoid Hemisinae.