Investigating the impact of captivity and domestication on limb bone cortical morphology: an experimental approach using a wild boar model

Abstract

The lack of bone morphological markers associated with the human control of wild animals has prevented the documentation of incipient animal domestication in archaeology. Here, we assess whether direct environmental changes (i.e. mobility reduction) could immediately affect ontogenetic changes in long bone structure, providing a skeletal marker of early domestication. We relied on a wild boar experimental model, analysing 24 wild-born specimens raised in captivity from 6 months to 2 years old. The shaft cortical thickness of their humerus was measured using a 3D morphometric mapping approach and compared with 23 free-ranging wild boars and 22 pigs from different breeds, taking into account sex, mass and muscle force differences. In wild boars we found that captivity induced an increase in cortical bone volume and muscle force, and a topographic change of cortical thickness associated with muscular expression along a phenotypic trajectory that differed from the divergence induced by selective breeding. These results provide an experimental proof of concept that changes in locomotor behaviour and selective breeding might be inferred from long bones morphology in the fossil and archaeological record. These trends need to be explored in the archaeological record and further studies are required to explore the developmental changes behind these plastic responses.

Cranial morphology of captive mammals: a meta-analysis

“…The cranial shapes observed in captivity may seem counterintuitive, where captive specimens of several species display wider skulls than their wild counterparts, with documented instances of correspondingly enhanced cranial musculature [87] and bite force [32]. This seemingly contradictory result may be related, at least in part, to the changes in muscle usage that occur in captivity [40,41,87]. While the pressure to capture prey and flee predators may be removed in captivity, certain captivity-specific tasks, such as the performance of stereotypic behaviors and the processing of novel diets may also increase muscle usage and may explain the morphological differences observed in this study [40,41,87,98].…”

“…This seemingly contradictory result may be related, at least in part, to the changes in muscle usage that occur in captivity [40,41,87]. While the pressure to capture prey and flee predators may be removed in captivity, certain captivity-specific tasks, such as the performance of stereotypic behaviors and the processing of novel diets may also increase muscle usage and may explain the morphological differences observed in this study [40,41,87,98]. Similarly, wild diets may constrain cranial shapes to maintain optimum functionality for processing and capturing prey items, particularly among species with highly specialized diets [2,32,60,109].…”

“…In captivity, unusual phenotypes, especially of the crania, may be expressed as a plastic response to environmental factors related to novel diet textures [24,46], nutrient availability [61,103], or any other factors unique to the captive environment [40,41,87]. Cranial responses to a captive environment may be explained by differences in muscle usage, which may impact osteological traits [17,87,117,119].…”

Impact of selection and domestication on hindlimb bones of modern reindeer populations: Archaeological implications for early reindeer management by Sámi in Fennoscandia

“…Knowing that mobility reduction and domestication induce differential stress changes that can affect the shape and robusticity of bones (e.g. Pelletier et al 2020;Harbers et al 2020aHarbers et al , 2020b, lifestyle was taken into account depending on whether the individuals were free-ranging (n = 75), captive (n = 28) or were used for racing and pulling (n = 20). Captive and free-ranging specimens are part of the collection of the Biodiversity Unit and working reindeer are donated skeletons archived at the Laboratory of Archaeology, both hosted by the University of Oulu.…”

“…Geometric morphometrics (GMM) is a quantitative approach that allows the comparison of bone shapes and the visualisation of significant morphological changes between groups of specimens by means of spatial coordinates of points called landmarks (Adams et al 2004;Zelditch et al 2012). In recent years, this methodology has been widely used to explore the morphofunctional changes induced by the domestication process (Evin et al 2013(Evin et al , 2015(Evin et al , 2017Owen et al 2014;Drake et al 2015;Hanot et al 2017Haruda 2017;Cucchi et al 2019;Haruda et al 2019;Pöllath et al 2019;Harbers et al 2020aHarbers et al , 2020bNeaux et al 2021;Pelletier et al 2020). Bone shape was therefore quantified by placing a set of landmarks on the 3D models.…”