EMBRYONIC-DEVELOPMENT TIMES AND EGG RETENTION IN 4 SPECIES OF SCELOPORINE LIZARDS

1. To test the hypothesis that rapid embryogenesis is an adaptation to cold climate, embryonic development time was measured in three oviparous species of Sceloporus that occur at different altitudes: S. woodi (lowland), S. virgatus (intermediate) and S. scalaris (high altitude). 2. Total embryonic development time (TEDT), defined as the time between ovulation to hatching, was measured at the same constant temperature (30-degrees-C) in the laboratory. Mean TEDT was 61.6 days in S. woodi, 55.3 days in S. virgatus, and 45.6 days in S. scalaris. 3. Embryo stages at oviposition, which provide a qualitative assessment of egg retention time, were noted for females ovipositing in laboratory aquaria. S. woodi exhibited brief egg retention, S. virgatus, intermediate egg retention, and S. scalaris, prolonged egg retention. 4. There was an apparent negative correlation between TEDT and elevation, as well as between TEDT and egg retention time. 5. The TEDT of S. jarrovi (56.6 days), a viviparous montane congener, was less than that of S. woodi, indicating that the developmental rate of S. jarrovi embryos was greater than that in a lowland species. 6. Despite differences in thermal characteristics of environments at different elevations, minimum estimates of TEDT in the field for S. woodi, S. virgatus, and S. scalaris were similar. 7. Measures of TEDT in these species of Sceloporus were consistent with the hypothesis that more rapid embryogenesis, like egg retention, acts to reduce the time it takes embryos to develop in cold climates. It is also hypothesized that more rapid development evolves in response to cold climate and is capable of lowering the threshold temperature at which viviparity evolves.