Long legs in baby mouse lemurs compensate for their physiological immaturity

Boulinguez‐Ambroise, G. , Zablocki‐Thomas, P. , Aujard, F. , Herrel, A. and Pouydebat, E. (2019), Ontogeny of food grasping in mouse lemurs: behavior, morphology and performance. Journal of Zoology, vol. 308, pp. 1-8. https://doi.org/10.1111/jzo.12652

The stars of the study by Boulinguez-Ambroise and colleagues are tiny, furry and large-eyed critters: the grey mouse lemurs (Microcebus murinus). These strictly arboreal primates are excellent climbers and use both their hands (bimanual) in food grasping. Furthermore, they grow super fast which makes them an ideal model organism to study ontogenetic changes of grasping performance. In contrast to their adult counterparts, the juvenile mouse lemurs are physiologically immature which places them at greater risk of injury and mortality. In particular, it is assumed that the hindlimb musculature is not yet sufficiently developed to ensure secure contact with the arboreal substrate. This lead to the hypothesis that the young animals may additionally use one hand to support body balance when the other hand grasps the mobile food item.

Fig 1
In the wild, grey mouse lemurs (Microcebus murinus) are only found on the island of Madagascar. These strepsirrhine primates are strictly arboreal and excellent climbers. Photo by G. Boulinguez-Ambroise.

To tackle this question, the authors of the present work first analysed the external morphology of the fore- and hindlimbs. “We measured the length of the segments to compare the limb proportions throughout development.”, explains G. Boulinguez-Ambroise, the first author of the study. “Next, we investigated possible differences in grasping performance across ontogeny using a force platform to quantify the maximal pull strength of the hands and feet.” In a third step, video analyses were performed to record the prehension strategy displayed to grasp the moving food item. Surprisingly, grasping behavior did not vary during development. “Juvenile mouse lemurs used bimanual grasps in the large majority of the sessions, the mouth alone being never used”, says Dr. E. Pouydebat, the leader of the project. In accordance with this, young animals showed relatively high grasping performance. Relative to their body mass, 1-month-old individuals displayed a grasping performance that was equivalent to that of 6-month-old individuals which corresponds to the adult state. Interestingly, the results indicated that juvenile mouse lemurs have disproportionally longer hindlimb segments when compared to older individuals. Furthermore, the authors found a positive relationship between size of the hindlimbs and feet performance (i.e., grasping strength). This suggests that the long legs may permit young primates to compensate for their immature musculature.

Fig 2
Young grey mouse lemurs (Microcebus murinus) at 15 days (left) and 1 month (right) of age. Photos by G. Boulinguez-Ambroise.

The study recently published in the Journal of Zoology shows that grey mouse lemurs are under selection for increased grasping ability early in life. The ability to grasp plays a vital role in many behaviors, most notably in arboreal locomotion and foraging and is closely linked to the origin of primates because it facilitated the exploitation of the terminal branch milieu.

Christine Böhmer

2 thoughts on “Long legs in baby mouse lemurs compensate for their physiological immaturity

Add yours

Leave a Reply

Please log in using one of these methods to post your comment:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

Blog at WordPress.com.

Up ↑

%d bloggers like this: