Developmental deformities in the parthenogenetic lizard Cnemidophorus uniparens (Teiidae) and the "anomalous male" phenomenon

Parthenogenetic species of lizard occasionally produce male progeny characterized by developmental defects and low viability. Production of anomalous males is an unresolved problem in sexual differentiation as parthenogenetic female lizards are expected to produce female offspring. The "anomalous male" phenomenon was examined by sexing nonviable embryos produced by the parthenogenetic whiptail lizard Cnemidophorus uniparens. Twenty-six deformed embryos were obtained; all were female except for three which did not possess gonads. Male embryos were not detected. Developmental deformities found in Cnemidophorus embryos included anophthalmia, micropthalmia, encephalocoele, hypoplasia of the lower jaw, head foreshortening, gastroschisis, and malformations of the vertebral column. Several embryos possessed a combination of defects. Four hypotheses are presented to account for production of anomalous males by reptilian parthenoforms. Three hypotheses involve production of sex-reversed males (genetic females). A fourth hypothesis asserts that anomalous males are derived from hybridization events between a female from a unisexual species and a male from a bisexual species. Of the four hypotheses, the hybridization hypothesis has the greatest utility in explaining production of anomalous males by parthenogenetic lizards.