New research shows that young elephants benefit more from having older sisters than older brothers.
Researchers at universities in Finland, the UK, and Myanmar found that Asian elephant siblings influence offspring early into later life.
Being raised with older siblings increased the long-term survival of calves compared to not having siblings.
Research on semi-captive Asian elephants in Myanmar also found that sisters had a greater impact than older brothers.
Female elephants raised with older sisters had higher long-term survival and gave birth for the first time an average of two years earlier than those with older brothers.
Reproduction at an earlier age usually involves more offspring throughout an elephant’s lifetime, the researchers say.
While male elephants raised with older sisters had lower survival rates but higher body weights than those with older brothers.
According to the researchers, this seemingly adverse effect could be explained by the fast-live-die-young strategy, in which a positive early increase in body mass can lead to survival costs later in life.
Dr. Verane Berger, at the University of Turku in Finland, lead author of the study, said: “Our study confirms that sibling relationships shape individual lives, especially in social species, such as elephants, where cooperative behaviors are necessary for the development, survival, and reproductive potential of individuals. ”
The long-term consequences of sibling effects have not been well studied in long-lived animals, perhaps because the logistical challenges of field studies make it difficult to investigate effects on the entire population.
In this study, the researchers overcame this by studying a population of government-owned, semi-captive timber elephants in Myanmar, where many life-history records are kept.
During the day, these animals are used as mounts, transports, and drags.
They live unattended in the forest at night and can interact and mate with both wild and domesticated elephants.
Calves are raised by their mothers until they are five years old when they are trained for working.
The Myanmar Timber Enterprise (MTE) imposes regulations on the daily and annual workload of elephants.
For the study published in the Journal of Animal Ecology, the researchers used a large, multigenerational dataset on semi-captive Asian elephants to examine the effects of the presence and sex of older siblings on body mass, reproduction, sex, and survival of the next calf.
The records included reproductive and lifespan information for 2,344 calves born between 1945 and 2018.
The researchers say that because the study was correlated, the influence of external factors outside of sibling influence, such as quality of maternal care and elephant’s workload and management, cannot be ruled out.