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Craniofacial Fluctuating Asymmetry in Cross River Gorillas (Gorilla gorilla diehli)
Amy J Spies1, Kate McGrath2,3, Amandine Eriksen4
1Department of Interdisciplinary Health Sciences, Arizona School of Health Sciences, A.T. Still University, Mesa, Arizona, USA.
Objectives:
Craniofacial fluctuating asymmetry (FA) in gorillas has been linked to environmental and/or genetic stress. Prolonged population declines increase levels of inbreeding, leading to developmental instability, which can manifest as FA. Among gorillas studied to date, craniofacial FA levels are highest in mountain gorillas (G. beringei beringei) and lowest in western lowland gorillas (G. gorilla gorilla), reflecting known levels of genetic diversity and inbreeding in these subspecies. This study assessed craniofacial FA in Cross River gorillas (G. gorilla diehli), a little-known subspecies with high levels of inbreeding due to a recent genetic bottleneck.
Materials And Methods:
Thirty fixed landmarks of the craniofacial skeleton were used to assess FA in 30 Cross River gorillas using Procrustes ANOVA. Principal component analysis assessed variation in both symmetric and asymmetric components. Differences in FA magnitudes between Cross River gorillas and published data for other Gorilla subspecies were assessed using permutation tests.
Results:
Craniofacial FA accounts for 9.9% of shape variation in Cross River gorillas, whereas directional asymmetry accounts for 0.5%. Allometry accounts for 14.1% of shape variation in the symmetric component and 3.8% in the asymmetric component. Craniofacial FA magnitudes are higher in Cross River gorillas than in western lowland gorillas and lower than in mountain gorillas.
Discussion:
High FA in Cross River gorillas aligns with known levels of inbreeding, supporting the link between genetic stress and craniofacial FA in gorillas. Persistent inbreeding and the loss of genetic diversity may decrease population fitness, further increasing the risk of extinction.
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