Elephants benefit from having older siblings, especially sisters

Date:
September 21, 2021
Source:
British Ecological Society
Summary:
A study of semi-captive Asian elephants in Myanmar has found that
calves benefit from having older sisters more than older brothers.



FULL STORY ==========================================================================
A study of semi-captive Asian elephants in Myanmar has found that
calves benefit from having older sisters more than older brothers. The
findings are published in the British Ecological Society's Journal of
Animal Ecology.


========================================================================== Researchers at universities in Finland, the UK and Myanmar have found that Asian elephant siblings influence younger offspring from early through to
late- life. Being raised with older siblings strongly increased calves' long-term survival compared to not having a sibling, with elder sisters
having a bigger impact than elder brothers.

In female elephants, those raised with older sisters had higher
long-term survival and reproduced for the first time an average of two
years earlier, compared to those with older brothers. Reproducing at an
earlier age is generally associated with more offspring over the course
of an elephant's lifetime.

In male elephants, those raised with older sisters had lower survival but higher body weight, compared to those with older brothers. This seemingly detrimental effect may be explained by a 'live-fast, die young' strategy,
where the positive early increase in body mass could lead to survival
costs later in life.

Dr Ve'rane Berger at the University of Turku and lead author of the
study said: "Our research confirms that sibling relationships shape
individual lives, particularly in social species, such as the elephants,
where cooperative behaviours are essential to the development, survival
and reproductive potential of individuals." The long-term consequences
from sibling effects are understudied in long-lived animals. One of the
reasons for this is that the logistic challenges of field studies make
it hard to investigate effects over an animal's entire lifespan.



==========================================================================
In this study, the researchers were able to overcome this barrier by
studying a population of government-owned, semi-captive timber elephants
in Myanmar, for which extensive life history records are kept.

These elephants are used during the day as riding, transport and draft
animals.

At night the elephants live unsupervised in forests and can interact and
mate with both wild and tame elephants. Calves are raised by their mothers until the age of five when they are trained for work. The Myanmar Timber Enterprise (MTE) imposes regulations on the daily and annual workload
of elephants.

Dr Mirkka Lahdenpera" at the University of Turku and co-author of the
study said: "Because the elephants live in their natural habitats, there
are many similarities to wild elephants, such as natural foraging and
no assistance in breeding. While there are differences -- in the wild,
family groups are probably bigger -- there are more similarities than differences and we could assume that some of the associations found in our study would also hold true for wild elephants. But of course, these should
be studied" The researchers used a large, multi-generational dataset
of semi-captive Asian elephants to look at the influence the presence
and the sex of elder siblings on the body mass, reproduction, sex, and
survival of the next calf. The records contained precise reproductive
and longevity information for 2,344 calves born between 1945 and 2018.

As the study was correlational, the influence of external factors outside sibling effects, such as the quality of maternal care and elephants'
workload and management, cannot be excluded.

On the next steps for this research project, Dr Berger said: "By
collecting more information on the body mass of mothers at birth, we
hope to disentangle maternal effects from sibling effects.

"More data will also let us explore the effects of the environment on
sibling relationships and go into more detail on the effects siblings
have on specific aspects of a younger calf's health, such as immunity,
muscular function and hormonal variations.

"We could also investigate the influence of the sex and
presence of younger calves on elder calf life history trajectory." ========================================================================== Story Source: Materials provided by British_Ecological_Society. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Ve'rane Berger, Sophie Reichert, Mirkka Lahdenpera", John Jackson,
Win
Htut, Virpi Lummaa. The elephant in the family: Costs and benefits
of elder siblings on younger offspring life‐history trajectory
in a matrilineal mammal. Journal of Animal Ecology, 2021; DOI:
10.1111/1365- 2656.13573 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/09/210921081017.htm

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