Growth Rates
A field study in Algeria indicates that Moroccan spiny-tailed lizards add approximately 1.5 to 2 inches (3.75 to 5 cm) of total growth each year until around the age of 8-9 years (Vernet, et al 1988). In captivity this rate can be exceeded due to a more reliable food source and probably better nutrition.
Growth rate in captivity is probably influenced by a variety of things such as nutritive value of food, temperature and possibly the presence of other lizards. For example, I compared the growth rate of eight individuals that hatched in 1996 with nine of their siblings that a friend raised. I kept the lizards separate from each other, ambient temperatures often exceeding 100F, and under full spectrum bulbs. The other nine were fed a similar diet and supplementation. However, they were all kept in the same cage, ambient temperatures were in the low 90Fs, and no full spectrum bulbs were used. Both setups provided incandescent spot lights to allow the animals to raise their body temperature above the ambient temperature. After 12 months the following data was collected.
Growth Rates of Siblings Raised Under Different Environmental Conditions
Measurements Siblings In Isolation at higher Ambient Temperatures (n=8) Siblings Raised as a Group at lower Ambient Temperatures (n=9)
Average Weight 122 grams 67 grams
Average Total Length 22.5 cm 18.6 cm
As the data indicates, there are significant differences between the two groups. My eight hatchlings were 21% longer in total length and weighed 82% more. Unfortunately, I can not determine which environmental factor was the cause of the difference or whether it was several factors in concert. However, I believe this data suggests that raising hatchlings separately at higher temperatures may increase growth.
Another interesting fact is the differential growth rates among individuals raised under exactly the same conditions. I have observed siblings in my own collection weigh twice as much after one and two years of growth. This can not be attributed to gender differences since I have observed it with both sexes.
I would think this info could be applied broadly to all Uromastyx species. Of course, there will be some variation between species and between individuals within a species.
With U. geyri, they have not been kept in captivity very long and breeding reports are scarce. This data just may not be available to us yet. This is why it's important that keepers such as yourself keep records of such information and share it with others.
