# Fluctuating Asymmetry and Stress in _Macaca fuscata_: Does Captivity Affect Morphology?
## 1 Introduction  
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; 12; 13; 14; 15; 16; 17; 18; 19; 20; 21; 22; 23; 24; 25; 26; 27; 28; 29; 30; 31; 32; 33; 34; 35; 36; 37; 38; 39; 40; 41; 42; 43; 44; 45; 46; 47; 48; 49; 50; 51; 52; 53; 54; 55; 56; 57; 58; 59; 60; 61; 62; 63; 64; 65; 66; 67; 68; 69; 70; 71; 72; 73; 74; 75; 76; 77;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 addition, sex might influence the degree and modes of asymmetry. Indeed, in some animals, the male's morphology is more subject to asymmetric development, probably because of a faster and more variable growth [24]. Recently, researchers have begun to explore the link between captivity and the presence of morphological asymmetry [25]. Inbreeding and the consequent loss of genetic variability could explain, at least in part, the presence of FA in the skeleton [23], although a recent study [14] compared the magnitude of FA in the mandible of outbred and inbred mice and found no significant degree of FA in the latter. Alternatively, asymmetry could be the effect of epigenetic changes caused by stress-inducing factors derived by living in non-natural environments. Although modern zoo facilities work to achieve ever-growing knowledge of captive animal welfare, we are not aware of the full impact that an enclosure and its dynamics can have on the development of an individual. Changes in the natural diet, contact with pathogens other than those encountered in the wild, and the inevitable restrictions or alterations of the optimal habitat pose challenging conditions that can cause an irregular development [26]. Much evidence exists about the impact of captivity on animal behaviour [27; 28]. However, how living in a captive environment can influence an individual or a group's morphology is still unclear [29; 30]. Fishes raised in captivity have shown significantly higher levels of fluctuating asymmetry on different morphological traits, some of remarkable functional importance, such as the length of the pectoral and ventral fins [31]. Ref. [29] provides an extensive review of the studies that investigated FA in captive mammals and birds, concluding that despite further and more conclusive studies are needed, FA is a promising measure of animal welfare [32]. The aim of this work is to test and characterise FA in the mandible of captive primates, namely _Macaca fuscata_, and to detect differences in the asymmetry patterns in wild and captive individuals that could indicate stress due to captivity. We chose the mandible because it is a main actor in the interaction of an animal and its environment. Few studies have tested the presence of FA in animals that were born or lived under altered environmental or genetic circumstances, and even fewer focused on mandibular morphology [14; 33; 34]. Functional alterations that derive from mandibular asymmetry could have an impact on the masticatory behaviour of individuals. Therefore, it is important to understand if and to what extent the mandible of captive individuals could become asymmetric under stressful conditions. We chose _M. fuscata_ because this species offers an ideal sample for studying the effects of captivity on the mammal skeleton. First, a suitable sample of captive and wild specimens is made available by the Digital Morphology Museum, KUPRI ([[http://dmm.pri.kyoto-u.ac.jp/dmm/WebGallery/index.html](http://dmm.pri.kyoto-u.ac.jp/dmm/WebGallery/index.html)]([http://dmm.pri.kyoto-u.ac.jp/dmm/WebGallery/index.html](http://dmm.pri.kyoto-u.ac.jp/dmm/WebGallery/index.html)), accessed on 20 March 2021); second, because _M.