Slow lorises (Nycticebus spp.) display evidence of handedness in the wild and in captivity

ABSTRACT

It has been suggested that strepsirrhines (lemurs, lorises, and galagos) retain the more primitive left-hand preference, whilst monkeys and apes more regularly display a right-hand preference at the individual-level. We looked to address questions of laterality in the slow loris (Nycticebus spp.) using spontaneous observations of 7 wild individuals, unimanual tests in 6 captive individuals, and photos of 42 individuals in a bilateral posture assessing handedness at the individual- and group-level. During the unimanual reach task, we found at the individual-level, only 4 slow lorises showed a hand use bias (R: 3, L: 1), Handedness index (HI) ranged from −0.57 to 1.00. In the wild unimanual grasp task, we found at the individual-level two individual showed a right-hand bias, the HI ranged from −0.19 to 0.70. The bilateral venom pose showed a trend toward a right-hand dominant grip in those photographed in captivity, but an ambiguous difference in wild individuals. There are many environmental constraints in captivity that wild animals do not face, thus data collected in wild settings are more representative of their natural state. The presence of right-handedness in these species suggests that there is a need to re-evaluate the evolution of handedness in primates.

KEYWORDS:

• Nocturnal primate
• handedness
• hand use
• Indonesia
• feeding

Acknowledgements

The authors thank the two anonymous reviewers whose suggestions greatly improved the manuscript. They also thank their field team including Y. Nazmi, A. Nunur, D. Rustandi, R. Cibabuddthea, D. Spaan, J. Wise, R. O’Hagan, D. Bergin, F. Cabana, L. Beasley, C. Marsh, J. Wise, D. Geerah, E. J. Rode, M. Rademaker, M. Siagud, and S. McCabe. They thank the team at the Cikananga Wildlife Center including N. Muqaddam and W. Eggen. The photos included in this project were taken by J. O’Neil, K. A. I. Nekaris and A. Walmsley. Ethical approval for this research was provided by the Animal Ethics Sub-Committee at Oxford Brookes University.

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

Stephanie A. Poindexter http://orcid.org/0000-0002-8183-4837

Kathleen D. Reinhardt http://orcid.org/0000-0003-3260-7854

Vincent Nijman http://orcid.org/0000-0002-5600-4276

Kathleen D. Reinhardt http://orcid.org/0000-0001-5523-7353

Additional information

Funding

This work was supported by Columbus Zoo and Aquarium; Nacey Maggioncalda Foundation; National Geographic Society [GEFNE101-13]; Shaldon Wildlife Trust; Margot Marsh Biodiversity Foundation; People's Trust for Endangered Species; Mohamed bin Zayed Species Conservation Fund [152511813]; Phoenix Zoo; Longleat Safari and Adventure Park; Shepreth Wildlife Park; Cotswold Wildlife Park & Gardens; Henry Doorly Zoo; The Cleveland Zoological Society and The Cleveland Metroparks Zoo; European Human Behaviour and Evolution Society; International Primate Protection League; Memphis Zoo; Conservation International Primate Action Fund; Disney Worldwide Conservation Fund; Augsburg Zoo; Brevard Zoo; Amersfoort Zoo; Zoologische Gesellschaft für Arten- und Populationsschutz; Primate Society of Great Britain; Sophie Danforth Conservation Biology Fund; Royal Geographical Society; Whitley Wildlife Conservation Trust.