Abstract
Fluctuating Asymmetry (FA) in morphology is used as a proxy for developmental instability in response to stress factors. FA has important implications for understanding the impact of differential environments and stressors on the skeletal phenotype. Here, we explore FA in the mandibular morphology of wild and captive Macaca fuscata to detect differences induced by the captive environment. We use two different approaches in Geometric Morphometrics to characterise the degree and patterns of FA and Directional Asymmetry (DA) based on 3D mandibular landmarks. Our results show that the wild and captive groups exhibit morphological dissimilarities in the symmetric component of shape while no significant degree of asymmetry (fluctuating or directional) was detected. Based on our results and on previous literature on the subject, we suggest that (I) captivity is likely to affect the mandibular morphology of M. fuscata; (II) FA may not be a suitable indicator to detect stress in the conditions analysed; and that (III) the mandible may not be the ideal region to study asymmetry because of its functional nature.
Highlights
The degree and modes of anatomical asymmetry have been extensively studied for decades both in vertebrates and invertebrates [1,2,3,4,5,6,7,8,9,10,11]
Results from the Procrustes ANOVA (Table 5) shows that prevalently sex (p-value = 0.001 ***, R2 = 0.13), and group and size (p-value = 0.001 ***, R2 = 0.05) impact on the overall mandibular shape, suggesting that sexual dimorphism, allometry, and environmental conditions directly influence the way in which the mandible develops and reach its final morphology
When the overall mandibular morphology is put in relation to asymmetry, both directional, fluctuating and group asymmetry show no significant results
Summary
The degree and modes of anatomical asymmetry have been extensively studied for decades both in vertebrates and invertebrates [1,2,3,4,5,6,7,8,9,10,11]. Following [16], we define stress as any condition that has the potential of altering or limiting the range of natural expression of the individual development and behaviour. Different morphological traits have been linked to different sensitivity to FA and some anatomical regions are more prone to become asymmetric [22]. This may occur because asymmetry in certain anatomical regions could severely affect the ability of an animal to perform a fundamental task, as is the case of limb proportions for locomotion [23]. In some animals, the male’s morphology is more subject to asymmetric development, probably because of a faster and more variable growth [24]
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