Lieu: Brunoy
Abstract: The environment of juvenile primates is very
challenging, especially when the parents do not carry their babies. Juveniles have
to forage and move on the same substrates as adults do and escape the same
predators, despite their immature state. In this study, we explore the developmental
strategies that may provide effective locomotor abilities early in life. This
could provide new insights into the selective pressures acting on juvenile
primates and into evolution of primate locomotion. We conducted an ontogenetic
study of 36 arboreal grey mouse lemurs from birth to adulthood (6 months). The
investigated parameters were for both limbs, 1) grasping behaviour during
locomotion (i.e., grip postures), 2) grasping performance (i.e., pull strength)
and 3) motor coordination (i.e., RotaRod® test). Our results show that as early
as 8 days of age babies are able to climb substrates of various slopes and
diameters outside of their nest. Although juveniles cannot successfully
complete a motor coordination test before 30 days of age, young individuals display
relative pull strengths that are very high or even on par with adults,
guaranteeing stability on narrow substrates. Moreover, individuals of all ages
use pedal secure grasps on all
substrates; however, the use of manual secure grasps decreases during
development. These behavioral transitions are particularly marked on vertical
and narrow substrates. From an evolutionary point of view our results suggest
that vertical and narrow branches may drive the evolution of strong grasping
abilities in primates. Our results further suggest different functional roles
of the hands and feet, with the hind limbs ensuring body balance on the
substrates, freeing the upper limbs for manipulation.
