Degree of terrestrial activity of the elusive sun‐tailed monkey (Cercopithecus solatus) in Gabon: Comparative study of behavior and postcranial morphometric data

Abstract

We carried out a multidisciplinary study linking behavioral and morphological data from a little-known guenon species, Cercopithecus solatus, endemic to Gabon. Over a period of 9 months, we documented the pattern of stratum use associated with postural and locomotor behavior by direct observation (650 hrs) of a semi-free-ranging breeding colony. We also conducted a morphometric analysis of the humerus and limb proportions of 90 adult specimens from 16 guenon species, including C. solatus. Field observations indicated that C. solatus monkeys spent a third of their time on the ground, similar to semi-terrestrial guenon species. We detected two patterns of stratum use: at ground level, and in trees, at a height of 3-10 m. The monkeys spent more time on the ground during the dry season than the wet season, feeding mainly at ground level, while resting, and social behaviors occurred more frequently in the tree strata. Our study of humerus size and shape, together with the analysis of limb proportions, indicated morphofunctional adaptation of C. solatus to greater terrestriality than previously thought. We therefore characterize C. solatus as a semi-terrestrial guenon, and propose a new hypothesis for the ancestral condition. By combining behavioral and morphological results, we provide new information about the adaptive strategies of the species, and the evolutionary history of guenons, thus contributing to the conservation of the sun-tailed monkey in the wild.

Determinants of terrestrial feeding in an arboreal primate: The case of the southern bamboo lemur (Hapalemur meridionalis)

“…The subsequent evolutionary shift in some primate species from an arboreal to terrestrial niche is shown through various morphological adaptations, for example, limb, dental, postcranial, etc. (Fleagle, ; Gebo, ; Gebo & Sargis, ; Motsch et al, ). The evolutionary pressures that led to a terrestrial niche, however, are poorly supported by empirical data.…”

The sun‐tailed monkey (Cercopithecus solatus): first report of mother‐infant dorsal carrying behaviour in a forest guenon, Gabon

“…The sun-tailed monkey (Cercopithecus solatus) is a forestdwelling, semi-terrestrial guenon (Gautier-Hion, 1988;Motsch et al, 2015). Due to its very cryptic nature (Gautier et al, 1992;Brugi ere, Gautier & Lahm, 1998), study or even direct opportunistic observations in wild have been extremely rare (Harrison, 1988).…”

Skeletal morphology of the lesula (Cercopithecus lomamiensis) and the evolution of guenon locomotor behavior

“…Despite their overall skeletal similarity, studies exploring guenon skeletal adaptations throughout the radiation find support for a functional signal related to substrate use (e.g., Elton et al, ; Gebo & Sargis, ; Manaster, ; Motsch et al, ; Nakatsukasa, ; Sargis et al, ). As with primates generally, terrestrial and arboreal guenon taxa are differentiated by their postcranial morphology, although semiterrestrial taxa have generally been found to be more similar to arboreal species (Gebo & Sargis, ; Manaster, ; Sargis et al, ).…”

“…With new specimens of the lesula postcranium and an established link between postcranial morphology and locomotor mode, we can apply a functional morphology approach to provide additional insight into its locomotor profile and substrate preferences. For example, a similar approach was applied to the sun‐tailed monkey ( Allochrocebus solatus ), a relatively recently described guenon from Gabon (M. J. S. Harrison, ; Motsch et al, ). Allochrocebus (formerly Cercopithecus [ lhoesti ] group) species have previously been described as terrestrial (Gartlan & Struhsaker, ; Gautier‐Hion, ; Kaplin & Moermond, ), and initial reports also observed the sun‐tailed monkey on the ground but were hampered by its dense forest environment and shy nature (Gautier‐Hion, ; M. J. S. Harrison, ; Peignot, Fontaine, & Wickings, , ).…”

“…Allochrocebus (formerly Cercopithecus [ lhoesti ] group) species have previously been described as terrestrial (Gartlan & Struhsaker, ; Gautier‐Hion, ; Kaplin & Moermond, ), and initial reports also observed the sun‐tailed monkey on the ground but were hampered by its dense forest environment and shy nature (Gautier‐Hion, ; M. J. S. Harrison, ; Peignot, Fontaine, & Wickings, , ). A recent study on a semi‐free ranging group in Gabon combined behavioral data with a morphometric analysis of the forelimb; it concluded that the sun‐tailed monkey exhibits semiterrestrial behavior characteristic of the lhoesti ‐group guenons, spending an average of one third of its time on the ground, and its humeral morphology is most similar to that of other semiterrestrial and terrestrial guenons (Motsch et al, ).…”