Elephants that give birth as teenagers die younger, but are fitter than mothers that delay, say scientists.
Researchers studied Asian elephants working in the timber industry in Myanmar, also known as Burma.
Mothers that gave birth younger were found to have larger families overall, and this greater genetic legacy is considered 'high fitness'.
Experts suggest a full understanding of the animals' reproductive health could reduce the strain on wild populations.
The findings are published in the Journal of Evolutionary Biology.
Asian elephants are listed as Endangered by the International Union for the Conservation of Nature; around 50,000 animals are thought to exist worldwide.
In Myanmar, approximately 5,000 of the animals are used in the state-owned timber industry to provide powerful transport in the dense jungle.
Advocates consider the practice to have less impact on the environment because it reduces the need for roads through the jungle and heavy haulage machinery.
The elephants are free to roam the forest at night and during rest breaks. During this time they mix - and mate - with wild elephants.
But fertility rates and the survival of young elephants are low for the semi-captive animals, meaning more elephants have to be captured from the wild every year.
'This is causing the wild population to decline at a rate which, it is estimated, could lead to the extinction of Asian elephants in the wild by the end of this century,' said Dr Adam Hayward, from the University of Sheffield, who co-authored the study.
So what ultimately matters is not lifespan, but the number of offspring you leave behind'
End Quote Dr Adam Hayward University of Sheffield
'The Myanmar government recognise this, and are keen to optimise the management of their captive elephants.'
For the past 70 years, government vets have kept detailed logbooks of the animals' health and breeding records.
Dr Hayward and his fellow researchers studied these official records to understand any patterns that could help to improve the animals' prospects.
They found that elephants that gave birth before the age of 19 were two times as likely not to survive beyond 50.
But the teenage mothers had more calves in their lifetimes, resulting in more opportunities to pass on their genes - which in biological terms is the key indicator of high fitness.
'We're using 'fitness' in an evolutionary sense - individuals who have higher fitness pass more copies of their genes on to the next generation,' explained Dr Hayward.
'So what ultimately matters is not lifespan, but the number of offspring you leave behind.'
These early results form part of a larger, longer-term project to understand why birth rate and survival are lower in captive populations than in the wild.
Dr Hayward suggested that the project's findings could also directly influence how the timber elephants are managed in order to maximise their fertility and protect wild populations.
'It is hoped that by working out why some individuals are better reproducers than others, and determining the main factors which shorten lifespan, the management strategy can be tailored to enhance sustainability of the captive population,' he said.
According to the biologist, the study is the first to review ageing in a long-lived land animal that is not a human.
'In terms of research on ageing, [we are] really interested in comparisons between humans and elephants, specifically with regard to the menopause,' Dr Hayward said.
'Female elephants can reproduce into their 60s, but female humans can't. Why not?
'Studying ageing in populations such as elephants may give insight into the evolution of ageing in our own species as well as wild animals.'
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