Evolutionary morphology of the lesula and the broader guenon radiation suggests multiple transitions to terrestriality

Abstract

The living guenons (Tribe Cercopithecini) are largely an arboreal radiation, but the recognition of patas, vervets, and L’Hoest’s monkeys as a clade suggests a single evolutionary transition to terrestriality within the tribe. Recently, a new guenon species was discovered in the TL2 region of the Democratic Republic of the Congo, the lesula (Cercopithecus lomamiensis). Little is known about its behavior and morphology, but preliminary observations and camera trap data suggest that the lesula is frequently found on the forest floor. The recovery of two skeletal specimens allows for evolutionary morphological analyses of the lesula postcranium and the guenon radiation more broadly. Twenty-one qualitative features and quantitative measurements correlated with terrestriality were taken on 151 individuals representing 22 guenon species, including C. lomamiensis. The percent of time spent on the ground was taken from the literature for each species, and every species was also assigned a categorical terrestriality score (arboreal: <20%; semi-terrestrial: 20-40%; and terrestrial: >40% on the ground). Size-corrected and species-averaged measurements were included in a principal components analysis. PC1 was highly correlated with percent terrestriality (R2 = 0.844, p < 0.001), and this regression estimated the lesula spends 39-52% of its time on the ground. A discriminant function analysis correctly classified 87.6% of specimens to locomotor category, and classified the lesula specimens as semi-terrestrial (posterior probability = 0.968) or terrestrial (posterior probability = 0.997). These results corroborate field observations of the lesula and its sister species, C. hamlyni, suggesting that terrestriality evolved multiple times among the guenons.

Full text

Introduction
The guenons (Tribe Cercopithecini) are a diverse and primarily arboreal radiation. A new
species of guenon, the lesula (
Cercopithecus lomamiensis
), was recently described from the
TL2 region in the Democratic Republic of the Congo (Hart et al. 2012). Little is known about its
behavior and morphology, but preliminary behavioral observations suggest it spends a
significant proportion of its time on the ground. Two adult skeletons have recently been
recovered, presenting the opportunity to use a functional morphology approach to inferring the
substrate use patterns of the lesula, and to evaluate the hypothesis of a single transition to
terrestriality among the guenons (Tosi et al. 2004).
Results
•PC1 and % terrestriality:
R2= 0.852, p < 0.001
•Lesula % terrestriality: 45.7%
(95% CI: 39.3-52.1%)
•DFA correct classification rate:
87.04%
Acknowledgements and Works Cited
Hart, J.A., et al. (2012).
PLoS ONE
7(9):e44271.
Tosi, A.J., et al. (2004).
Journal of Human Evolution
(46):223-237.
This project was funded by the NYCEP NSF IGERT Grant, an AAPA
Professional Development Grant, and a Hunter Presidential Travel
Award.
Evolutionary morphology of the lesula and the broader
guenon radiation suggests multiple transitions to terrestriality
JULIA L. ARENSON1,2, CHRISTOPHER C. GILBERT1,2,3, ERIC J. SARGIS4,5, KATE M.
DETWILER6, TERESE B. HART5,7 and JOHN A. HART5,7
1PhD Program in Anthropology, The Graduate Center, CUNY, 2New York Consortium in Evolutionary Primatology, New York, NY, 3Department of Anthropology, Hunter
College, CUNY, 4Department of Anthropology, Yale University, 5Division of Vertebrate Zoology, Yale Peabody Museum of Natural History, 6Department of Anthropology,
Florida Atlantic University, 7Lukuru Wildlife Research Foundation, Kinshasa, Gombe, DRC
Materials and Methods
•152 individuals of 22 guenon
species, including two
C.
lomamiensis
•Estimates of percent time spent
on the ground taken from
literature and species classified
into categories:
•22 size-corrected and species-
averaged qualitative and
quantitative characters highly
correlated with percent
terrestriality used in PCA
•Regression between PC1 and %
terrestriality used to infer lesula’s
average percent terrestriality
•Discriminant function analysis on
size-corrected individuals to
classify lesula specimens by
substrate use category
ID
Category
Posterior
probability
YPM 15013
(F)
2
0.971
YPM 16889
(M)
3
0.938
Discussion
Functional analysis of the lesula’s postcranial morphology suggests
the lesula spends nearly half its locomotor time on the
ground.
This estimate corroborates camera trap studies and is also similar to data on its sister species, the owl-faced
monkey (
C. hamlyni
). A survey of guenon substrate use preferences shows they are generally more flexible than a single
terrestrial clade would suggest. These results
indicate multiple transitions to terrestriality among the guenons.
Lesula (Cercopithecus lomamiensis)
Drawing by K. Honda
Camera trap still of a female lesula and infant.
Terese Hart, bonoboincongo.com
Category
Percentage
Arboreal (1)
0
-20%
Semi
-terrestrial (2)
21
-40%
Terrestrial (3)
> 41%
Alternative topologies of the guenon radiation based on X and Y chromosome data from Hart et al. (2012). Tosi et al. (2004) suggested the terrestrial guenons formed a
monophyletic clade. Our results corroborate behavioral observations from the field that terrestriality has evolved in the guenons more than once (terrestrial taxa highlighted in blue).
YPM 16889 (M)
YPM 15013 (F)