Zoo cutie not quite as cute as we think
Zoo favourites are among the most aggressive animals in the world, says.
Whittle
What does United States president-elect Donald Trump share in common with other powerful male animals?
No, this isn’t intended as an insult. The answer is testosterone, the naturally occurring steroid that, among other effects, influences dominant behaviour in males.
Recent research has shown unusually high levels of testosterone in one particular species, an animal that is a crowd favourite at zoos throughout the world, including Christchurch’s Orana Wildlife Park.
And if you think this testosterone-pumped creature must be the massive silverback gorilla, one of the trio of newly acquired lowland gorillas at Orana, then good guess. But you’re wrong.
While testosterone is indeed significant in influencing how these male primates look and behave, the species at the centre of the latest study is in fact the muchloved meerkat, a member of the mongoose family.
Testosterone, a hormone that also promotes muscle growth and body hair, is most often associated with male animals’ size, strength and assertive behaviour. In addition, it is an anabolic steroid and is classified as a prohibited substance for human athletes by the World Antidoping Agency.
But what makes the latest testosterone research, published last month by scientists at Duke University in the US, so significant is that it concerns female meerkats, which have been found to have twice as much of the hormone as males.
Meerkats, therefore, are the only known species in which the levels of this steroid is reversed from the normal male-high/ female-low pattern.
The new findings help explain how the top-ranking queen manages to aggressively dominate subordinate female meerkats, often preventing them from becoming pregnant and forcing them to feed or care for the queen’s offspring instead. As with meerkats, dominant lemur and African wild dog females use aggressive behaviour to maintain control over subordinates, although the role of testosterone is less clear with these species.
But while the meerkats at Orana do display the hierarchical social behaviour typical of the species in the wild, they have not shown the same levels of ‘‘mean girl’’ antagonistic bullying reported in the Duke University study. ’’We have been very fortunate in not having encountered major issues with aggression from ours,’’ Orana education manager Toby Johnson said. Dealing with hostile intraspecific behaviour is an issue faced by zoos and wildlife parks worldwide.
The dilemma is caused by the need to create as natural a social environment as possible, on the one hand, and to prevent potentially distressing aggression (for visiting onlookers), on the other. The two male tigers at Orana, for example, are kept in separate enclosures, while testosterone-fuelled competition amongst male lions is minimised more drastically, through castration.
In addition to reducing intragroup aggression in the lion pride, the reduced testosterone has another side-effect: it prevents the males developing a mane, usually the most obvious means of distinguishing between the sexes.
According to Johnson, testosterone also has a dramatic effect on gorillas. ’’Gorilla males hit maturity around 10 to 12 years of age and undergo enormous development – body mass nearly doubles [and] sagittal crest and nuchal ridge development is incredible.’’
Both the sagittal crest and the nuchal ridge help give silverback males their characteristic massive facial features; the former is a bony crest running the length of the skull to which jaw muscles are attached, while the later is the ridge where the neck muscles attach to the skull.
Orana’s Zoo School uses skull casts of male and female gorillas to illustrate to students the pronounced sexual dimorphism (or difference between the sexes) in this species.
Testosterone has a similar effect on another endangered species that Orana plans to introduce in the near future – orangutans. And just as the testosterone levels of the park’s female meerkats do not appear to be causing unexpected problems, the two younger gorillas have several years to go before any major effects of the hormone would begin to show.
Unlike castrated lions, however, which are not needed for reproduction, the gorilla youngsters are potential contributors to an international breeding programme for this critically endangered species.
Please note – despite having linked animal research to the participants in the recent US election, it is entirely up to readers to create their own connections between testosterone and male beasts in zoos, and Donald Trump and his oft-commented-upon mane of hair.