Testosterone secretion, musth behaviour and social dominance in captive male Asian elephants living near the equator.

Testosterone concentrations were measured in blood samples collected weekly over a 5 year period from six adult (19-40 year old) male Asian elephants (Elephas maximus maximus) living in captivity in Sri Lanka (7 degrees N), to investigate the relationship between androgen secretion and the occurrence of musth (temporal gland secretion, drip urination and aggressive behaviour). The testosterone profiles were very variable both within and between animals. Long-term phasic changes in blood concentrations of testosterone, associated with periods of musth, occurred in three of the six elephants, with the most pronounced cyclicity in the oldest animal. Musth occurred annually after periods of high androgen secretion and there was a positive correlation between the duration of musth and mean concentrations of testosterone during the previous 2 months. The time of musth, while consistent for an individual, was variable between animals. In four bulls living within one social group, there was a positive correlation between social rank and mean concentrations of testosterone over the 5 year study, and only the dominant animal showed periodic musth. Short-term changes in testosterone concentrations occurred in blood samples collected every 15 min for 7 h, and following the injection of 20 micrograms GnRH, consistent with regulation through the pulsatile secretion of LH. Overall, the results support the view that fully mature male Asian elephants living near the equator express an asynchronous, cyclical, circannual pattern of gonadal activity, with the cyclical pattern developing progressively from 20 to 40 years of age. The periodic increase in testosterone secretion during the gonadal cycle induces the development of musth; however, androgen withdrawal following a period of hypersecretion may be the cause of some aspects of musth behaviour (aggression, unpredictability, disobedience) which make bull elephants very difficult to manage in captivity.