Saturday, January 16, 2021

How young Asian elephants learn to bend their trunks left or right

How young Asian elephants learn to bend their trunks left or right

Most people are either left-handed or right-handed. They are consistent in this laterality. Similarly, adult Asian elephants consistently use their trunks either preferring the left side or the right side. Fascinated by the question of when and how this laterality develops in young elephants, a group of researchers from Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR) studied free-ranging, individually identified Asian elephants from the Nagarhole and Bandipur National Parks and Tiger Reserves. The researchers found that calves develop a laterality in the way they use their trunks from three months onwards. They are more or less fixed in this laterality by the time they are a year old. This study, tracing out how this behaviour develops as the calf grows, is a first-of-its-kind study of free-ranging Asian elephants (Elephas maximus). The results have been published in The International Journal of Developmental Biology.

Equally likely

Unlike humans, where right-handedness dominates, elephants do not show a bias in this behaviour at the population level: Asian elephants are equally likely to show left-handedness as they are to show right-handedness.

In a prior study by Keerthipriya and coworkers led by TNC Vidya in JNCASR, such a lateralisation was seen in a calf of less than two months in captivity. However, due to the small number of young ones studied then, the gradual development of the behaviour could not be observed. As Dr. Vidya says, “During that study, we had sampled a single young calf and saw that even that had some lateralisation. So, in this study, we systematically checked if calves, in general, showed trunk lateralisaton.”

Elephant calves show handedness very early. She further explains that this suggests that the elephant calves don’t seem to start out trying out different sides and then settling on one side randomly, later becoming left-handed or right-handed through practice. “Instead, the side preference seems innate.”

In this study, T. Revathe, a PhD student, and S. Anvitha, MS-PhD student, at JNCASR, observed 30 calves (less than a year old ) and juveniles (between one and five years old). Among these there were16 females and 14 males from nine different clans.

The study throws open several questions. From their previous observations of adult and young elephants, the group deduced that the laterality was not inherited from the mother. Further studies may explore if it is inherited from the father.

Developmental inertia

The researchers found that trunk motor control develops postnatally over months although limb motor control and trunk side preference is achieved within a few hours of birth. “One possible reason for this could be phylogenetic inertia,” says Dr. Vidya. The term phylogenetic inertia refers to limitations on future evolutionary pathways imposed by previous adaptations. Or, in other words, how elongated noses (trunks) developed over evolutionary time and whether there are any constraints as a result of previous adaptations that affect the development of trunk.

In order to study this, one would have to examine sets of related species with elongated noses. “Unfortunately, there are only three living species of elephants,” remarks Dr. Vidya. “However, one could look at elephant shrews, or tapirs, which have elongated noses, and their relatives. One could examine whether these development of strength in these elongated noses occurs gradually after birth,” she explains.

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