Physiological and biochemical correlates of musth

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There is extensive anecdotal information from Asia that good nutrition and body condition are necessary for the successful expression of musth in bull elephants. The precise physiological links between body condition and musth are not clear as yet, although some possibilities are mentioned in this discussion.

It is well known that rutting males have increased levels of blood testosterone, which may mediate aggressive behavior. Males may also advertise their rutting condition by releasing scents from various glands. Before we discuss the specific functions of these physiological changes, we should consider the extent and nature of these rutting signals.

During 1969-1970, veterinarian M. R. Jainudeen and associates carried out the first detailed measurements of blood testosterone during the nonmusth and musth phases in captive Sri Lankan bull elephants. They found that bulls showing no signs of musth had testosterone levels of only about 0.2-1.4 ng/ ml in blood plasma. During the premusth phase, this rose to 4-14 ng/ml, while bulls in full musth showed dramatically elevated levels of 30-65 ng/ml of plasma testosterone. Within a week of coming out of musth, these values returned to the baseline values of nonmusth bulls.

Similar investigations by Bets Rasmussen and colleagues on Asian bull elephants at the Washington Park Zoo in Portland showed testosterone levels of 20-40 ng/ml during musth. A related hormone, dihydrotestosterone, which normally remained at about 0.2 ng/ml during the nonmusth phase, also shot up to 1.5 ng/ml when a bull was in heavy musth.

Cheryl Niemuller and R. M. Liptrap extended these findings through weekly monitoring of testosterone levels and relating these to a qualitative score of musth intensity in eight captive Asian bull elephants for up to 2 years (table 3.2). While a higher concentration of androstenedione than testosterone was generally seen during the nonmusth phase, the ratio was reversed in favor of testosterone during the musth phase; further, it correlated neatly with the intensity of musth.

The longest duration study of blood testosterone profiles is the weekly sampling over 5 years of six captive Asian bulls in Sri Lanka by G. A. Lincoln and W. D. Ratnasooriya. This clearly showed that short-term fluctuation of testosterone in an individual and high variability between animals may be the natural, erratic pattern in the tropics. Only the oldest bull showed a distinct cyclicity in the blood concentrations of testosterone; thus, the cyclic pattern of musth may develop gradually as the animal ages.

Attempts to measure testosterone in captive adult male African elephants when they showed temporal gland secretion have not as yet yielded useful results because of the confusion over the recognition of true musth by these researchers. Presumably, the male African elephant would show a similar upsurge in androgen levels if musth were properly recognized in zoo animals and sampled. Weekly monitoring of testosterone levels in the blood serum of a captive African forest elephant (Loxodonta africana cyclotis), aged 19 years, by K. A. Cooper and associates showed an irregular pattern and lower concentrations overall in contrast to two Asian bulls of similar age; the Asian bulls showed the more characteristic seasonal peaks associated with temporal gland activity.

In wild elephants, it would be an extremely demanding task to collect blood from bulls. Joyce Poole thus hit on an ingenious method of measuring testosterone in the urine of bulls. Soon after a bull urinated, she drove it away and quickly aspirated the urine from the ground with a syringe. The collected urine was filtered and frozen before being sent to a laboratory for analysis. As expected, bulls that were sexually active (but not in musth), in the premusth stage, or in regular musth generally had higher urinary testosterone levels than those not in musth and sexually inactive.

The daunting task of sampling elephants in the wild did not deter Anthony Hall-Martin from mounting a sustained operation during the 1980s of immobilizing elephants for sample collection at Kruger and Addo National Parks in South Africa. By now, there was a clearer recognition of musth versus mere temporin secretion in African elephants. Of the 111 bull elephants 21-40 years of age sampled over several seasons and years for blood and temporal gland secretion, 6 bulls were radio-collared and regularly sampled over a 5-

Table 3.2

Concentrations of androgens in the blood or urine of male elephants during nonmusth and musth phases.

Captive Asian elephants: serum androgen (North American zoos)

Androgen Levels, Androgen Levels, Nonmusth (ng/ml) Musth (ng/ml)

Elephant Group Age (years) Severity of Musth TATA

A 16 Mild 3.5

2.4

20.7 6.0

B 17 Mild 2.5

3.4

15.4 5.1

C 18 Mild 6.4

10.0

14.5 16.0

D 17 Medium 6.7

4.2

38.2 8.4

E 22 Strong 7.8

10.3

116.6 37.0

F 35 Strong 2.4

2.6

152.5 35.3

Wild African elephants: urinary androgen (Amboseli, Kenya)

Testosterone Levels

Elephant Group Musth Category

(ng/ml creatinine)

A Sexually inactive, not in musth

77.7

B Sexually active, not in musth

146.7

C Mature, sexually active, not in musth

176.4

D Premusth

225.7

E Musth

241.3

Wild African elephants: serum androgen (Kruger, South Africa)

Testosterone Levels

Elephant Group Musth Category

(ng/ml creatinine)

A Nonmusth (46%)

0.1-2.0

B Premusth, postmusth (39.5%)

2.0-10.0

C Musth (13.1%)

20.0-50.0

D Heavy musth (6.5%)

50.0 > 100.0

Sources: Based on Niemuller and Liptrap (1991); Poole et al. (1984); Rasmussen et al. (1996). T, testosterone; A, androstenedione.

year period (1985-1989). Bets Rasmussen and David Hess analyzed these samples for androgens and other organic compounds. Two-thirds of female elephants acting as controls had testosterone levels less than 0.1 ng/ml, while the rest showed levels in the range of 0.1-2.0 ng/ml. All bulls had testosterone levels above 1.0 ng/ml. As expected, the levels of testosterone and dihydrotes-tosterone in blood were distinctly higher in bulls during the musth phase, the former even crossing 100 ng/ml during very heavy musth (table 3.2). Interesting differences in blood androgen levels were observed in relation to the social context of the secreting bulls. These bulls had lower testosterone levels when they were near other adult bulls (about 5 ng/ml) compared to when they were solitary (70 ng/ml) or near family herds (70 ng/ml). These results should be interpreted with caution because of the low sample sizes of the comparisons. In the bulls that were sampled regularly, the characteristic cyclic pattern of androgen concentration was seen, with an elevated level associated with typical musth behaviors such as aggression.

The correlation between blood testosterone levels and temporal gland secretion or other signs of musth is not always clear in some observations of captive bulls. Some of the ambiguity could be due to a failure to distinguish between temporal gland activity and true musth (see sections 3.3 and 4.3.3). Nevertheless, on the basis of these observations it seems reasonable to look beyond the hypothalamic-pituitary-gonadal (i.e., reproductive) axis for a functional explanation of musth. Lisa Wingate and Bill Lasley have suggested that the adrenal glands also may play a role in the expression of musth. Apart from the gonads (testes), the adrenal glands are known to secrete androgens such as testosterone, dihydrotestosterone, and androstenedione. Good nutrition or over-nutrition may stimulate adrenal activity for increasing the production of cortisol (a hormone that regulates blood glucose), while androgens may be secreted at the same time. Musth is thus a secondary effect of adrenal activity. Temporal gland secretions have similarly been analyzed in both Asian and African elephant bulls. Here again, the results of chemical analysis of TGS in Asian bulls in musth are probably more revealing as TGS in African elephant bulls may not necessarily represent the musth phase. In fact, some of the earlier investigations of TGS composition in African elephants were certainly not carried out during the musth phase. In one such early study at Kruger, the sampled elephants were "stimulated into temporal gland secretion by helicopter driving." This TGS was obviously temporin, which does not seem to have any significance in sexual communication.

During the musth phase, androgens are much more concentrated in TGS than they are in blood among Asian elephants. Testosterone levels average about 500 ng/ml in TGS (and may even exceed 2000 ng/ml) or a 5-10-fold concentration compared to serum testosterone. Dihydrotestosterone also shows very high levels, averaging 350-400 ng/ml, a greater than 100-fold concentration compared to serum levels. Various volatile compounds, such as the phenols, are also found in TGS associated with musth. The most exciting of recent findings by Bets Rasmussen, Heidi Riddle, and V. Krishnamurthy on the chemical nature of TGS in Asian elephants, published in the journal Nature, is the difference between younger and older musth bulls in the compounds secreted. While sweet-smelling compounds such as esters and 3-hexen-1-ol were found exclusively in the TGS of younger musth bulls (or moda musth as stated in ancient Indian elephant lore), foul-smelling compounds (such as the frontalins and nonanones) were found only in older musth bulls. The veracity of observa tions of musth in ancient Indian writings was thus confirmed through modern science.

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