Experimental elevation of wildlife testosterone using silastic tube implants

Testosterone (T) is a key androgen that mediates vertebrate molecular, cellular, and behavioral processes. Its manipulation is therefore of interest to a vast number of researchers studying animal behavior and reproduction, among others. Here, the usage of silastic implants across wildlife species is reviewed, and a method to manipulate rock hyrax (Procavia capensis) testosterone levels using silastic implants is presented. Using a series of in-vitro and in-vivo experiments, the secretion patterns of silastic tubes and silastic glue were tested and were surprisingly found to be similar. In addition, we studied endogenous T levels in wild-captured rock hyraxes (Procavia capensis), and using T implants succeeded in elevating T to the maximal physiological concentrations recorded during the mating period. The number of implants that were inserted was the only predictor of T levels, and seven 20 mm implants were found to be the optimal dose. Implants induced sexual behaviors in the non-reproductive period. The duration of time that the implants were in the hyrax was the only significant factor that influenced the amount of T left over in the implant once it was removed. All together we affirm that T implants may offer a versatile tool for wildlife behavioral research by elevating T levels in the non-breeding period to maximal breeding levels.