Date of this Version
The Prairie Naturalist 40(112): March/June 2008, pp15-22
The Texas horned lizard (Phrynosoma cornutum) is a Texas state-threatened species and acquisition of data related to the species' ecology is essential. To accomplish this task individual animals need to be marked. Many marking techniques are available for lizards, however the majority of techniques have been tested on adults only. Studies involving hatchling and juvenile horned lizards are scarce due to problems associated with marking and relocating individuals in these age classes. I demonstrated that injection of passive integrated transponders (PIT's) can safely be used as a marking method in young Texas horned lizards. Thirty-two captive bred hatchling lizards were used. Hatchlings were allowed to grow to 20 mm snout-vent length (SVL) before PIT's were inserted into 16 hatchlings while the other 16 hatchlings were used as control animals. Hatchlings were measured and weighed weekly for 14 weeks and blood samples obtained weekly for 3 weeks to assess if PIT's affected lizard growth and health. No differences were noted in treatment effects for SVL (F1450 = 0.85, P = 0.37), weight (F1,450 = 1.60, P = 0.22), or white blood cell and differential counts (F1,30 < 1.47, P > 0.23). However, an interaction between treatment and week occurred (F I4.450 = 1.79, P = 0.04) for SVL. Texas horned lizard hatchlings that were PIT-tagged were larger in SVL during weeks 3, 7 to 10, and 12 than control lizards. No ditferences in SVL were noted between treatment groups during the remaining weeks. A duration effect was noted for both SVL (F 14,450 = 7654.0, P = 0.0001) and mass (F14,450 = 1595.1, P = 0.000 I). Snout-vent length for both PIT-tagged and control lizards increased weekly until week 12 when growth rate began to slow down. Mass gain for both groups of lizards was similar, with weekly spurts occurring except between weeks 0 and 1,7 and 8, 12 and 13, and 13 and 14. Passive integrated transponders did not interfere with the growth or health of young Texas horned lizards; therefore, they can be safely used as a marking tool.