Asian elephants born to stressed mothers feel the impact for the rest of their lives. New research has shown how elephants born into stressful situations not only have fewer offspring over their lives, but they also age faster.
“Poor early life conditions have been linked to many disease outcomes in humans, but is unknown whether stress in early life also speeds up aging rates in long-lived species,” explains Dr. Hannah Mumby, lead author of the study published in Scientific Reports. To investigate this, they turned to another long-term data set of a long-lived species, the Asian elephant (Elephas maximus).
In Myanmar (Burma), there is an extensive history of using Asian elephants as transport and draft animals in the timber industry. Currently, there are around 5,000 in semi-captive use in Myanmar, where they are used for work during the day, but released into the forest at night to forage in their family groups and mix with other captive and wild elephants in the region. The government timber corporation has kept meticulous records of all state-owned elephants, including which females had offspring and when. These records span almost a century and include around 10,000 individual elephants.
To work out at what point during the year the captive elephants were under most stress, the researchers collected the poop of mature females and analyzed it for indicators of stress, called glucocorticoid metabolites, over the period of a year. From this, they were able to ascertain that the most stressful few months coincided with when the animals started work again at the beginning of the monsoon season, during which time they work hard dragging heavy logs to the rivers.
They found that the female calves born during the high-stress period of the year had a lower chance of survival. But even those that did survive were then impacted for the rest of their lives. While these offspring were found to have higher rates of reproduction at an early age, overall they produced significantly fewer offspring over their entire lifetime. This is probably due to the fact that these elephants declined much more rapidly in older age.
“We found that the decline in reproduction with age is much steeper in the elephants born at the poorer time of year,” said Mumby, a researcher at the University of Sheffield. “Even though they reproduce slightly more when they're young, this still doesn't compensate for the steep decline and they end up with fewer offspring.” These results hint at the impact that a mother's stress might have on her offspring’s aging, and could have ramifications for how to manage Asian elephants, both in the wild and in captivity as their numbers continue to dwindle.