ABSTRACT
All adult specimens known for Gymnophthalmus underwoodi are females, and their mode of reproduction has been a mystery. In order to rule out the possibility of a bisexual mode of reproduction by means of mating with undiscovered males, hermaphroditism, or sex reversal during ontogeny, we examined hundreds of serial histological sections of complete reproductive tracts from juveniles and adults representing two generations of a lineage raised in captivity. In addition, comparative dissections were performed on other individuals and other species, and reproduction to the F5 generation was documented in laboratory colonies of G. underwoodi established from Trinidad and Surinam stocks. A lineage of three successive generations was produced entirely by individuals that were maintained in isolation from the moment of hatching. All specimens of G. underwoodi proved to be female, with reproductive anatomy identical to that of females of closely related, bisexual species of Gymnophthalmus: G. pleei and G. speciosus. Thus, G. underwoodi is an all-female species that reproduces by means of strict parthenogenesis, in the absence of sperm. As in the macroteiids of the genus Cnemidophorus studied previously, Gymnophthalmus has functional mesonephric kidneys throughout life. G. underwoodi ranks among the smallest amniotes, adults weighing about 1.2 gm and having a body length of 36-43 mm. Data from the laboratory colonies indicate the following: clutch size, 1-4 (X = 2); mean egg size about 9.4 × 6.5 mm (weight, 0.23 gm); development time, up to 61 days or more; hatchling body length, 16-19 mm (X = 18); hatchling tail length, 18-25 mm (X = 22); hatchling weight, 0.09-0.14 gm (X = 0.115); reproduction continuous year round with individuals able to produce successive clutches in less than a month but quiescent periods following reproductive sessions; maturity attainable seven mo after hatching; longevity at least 4 yr and 5 mo; and a dramatic decline occurred in egg viability in successive generations in the laboratory.
