Grasping the handedness of varecia
Background… Brain lateralization: the functional specialization of the brain
Evolutionary Significance?
left
right
The cerebral hemispheres of the brain control different functions
• Avoids costly duplication of neural circuitry • Enhances ability to perform two tasks simultaneously
Background… Non-human primates lateralize too!
Chimpanzees have adapted techniques for catching and eating termites.
• Evolution of primate handedness still unclear • Non-human primates exhibit “mixed” handedness • Handedness in primates influenced by body posture, task difficulty, and experience
Hypotheses Hypothesis & predictions bipedalism theory: • Quadrupedal bipedal
• Required higher balance • Increased cerebral lateralization P1: Both species of Varecia exhibit handedness P2: Handedness consistent among siblings
A group of Red Ruffed lemurs (Varecia rubra) sunning on horizontal limb
Subjects Methods 1& location Location: Duke Lemur Center, indoor and outdoor enclosures NHE 6
triplets • White Ruffed Lemur (Varecia variegata) • 4 males
NHE 8
twins
twins
• Red Ruffed Lemur (Varecia rubra) • 2 males, 2 females
Methods Data collection method: continuous scan sampling
• • • •
Rest Manipulate Social Feed
• • • •
Groom Locomotion Suspension Other
• Manipulating, supporting • Supported and unsupported
Red Ruffed lemur (Varecia rubra) showing leading limb preference
results Varecia species exhibit a manipulating limb preference V. rubra - left limb preference – 23.1 ev/hr SE 3.3
• V. variegata – right limb preference – 44.0 ev/hr SE 3.5
• Significant
Rate of manipulating limb use (events/hour)
•
Rate of manipulating limb use between family groups of Varecia 50 45 40 35
30 25
Left limb
20
Right limb
15 10
5 0
V. rubra
V. variegata Species
results Varecia species exhibit a supporting limb preference V. rubra - right limb preference – 10.5 ev/hr SE 1.5
• V. variegata– left limb preference – 19.8 ev/hr SE 1.0
Rate of supporting limb use (events/month)
•
Rate of supporting limb use between family groups of Varecia 25 20 15 Left limb
10
Right limb
5 0
V. rubra
V. variegata Species
results Rate of manipulating limb use among V. variegata siblings 60 50 40 30
Left limb
Right limb
20 10 0
Rate of manipulating limb use among V. rubra siblings Rate of manipulating limb use (events/hour)
Rate of manupulating limb use (events/hour)
Manipulating limb preference is consistent among siblings
45 40 35 30 25 Left limb
20
Right limb
15 10 5 0
1
2
3
Individual
4
1
2
3
Individual
4
conclusions • V. rubra and V. variegata exhibit handedness • Vacercia handedness is consistent among siblings Close up of Red Ruffed Lemur (Varecia rubra) hand
Prediction 1 Varecia handedness Close up of White Ruffed Lemur (Varecia
variegata ) using both hands as support
• Reflects brain lateralization – Manipulating limb vs supporting limb
Prediction 2 Species’ consistency among siblings
• Possible heritable component to handedness – Prior studies • Mixed preference • Number and consistency of study groups • Relatedness
• Further research
White Ruffed Lemur (Varecia variegata) triplets