Wild boar (Sus scrofa) experimental domestication: functional and ontogenetic approach of limb bone development in captive conditions – DOMEXP

DomExp will rely on 5 interacting working groups (WG):
WG1 is dedicated to the set up of the experiment that will control for the captivity-related phenotypic change due to an artificial reduction of mobility and the acquisition of biochemical samples (blood, hair) to measure health and stress of the subjects.This biochemical profiles will be coupled with 3D imaging data set of the growth and development of the musculo-skeleton system by means of medical CT (X-ray computed tomography) scan and MRI (Magnetic resonance
Imaging) scans run every 3 months until they are 2 years of age.
WG2 and WG3 are two complementary work packages that investigate biomechanical consequences of morphological changes In association with the different functional constraints. WG2 will investigate the cortical structure of long bones and trabecular geometry of tarsal bones, while WG3 will consider the external functional morphology of appendicular bones with a geometric morphometric approach.
WG4 will integrate the phenotypic data drawn from WG2 and WG3 to identify bio-indicators of a captive life style. These indicators will then be tested on archaeological series selected among French collections for the quality of their chrono-cultural contextualisation at the transition from hunting to herding and for their debated domestic vs. wild status.
WG5 will be dedicated to the data-basing of the whole project compiling field observations, longitudinal observations (biopsies, 3D images) from WG1, the 3D biometric data produced by WG2 and 3
and the 3D images and biometric data produced in WG4. This database, will be available to other researchers via open data website.

At this stage of the project (18 months), the most striking element is the creation of an experimental farm of wild boar at the reserve de la Haute Touche (Indre) with the acquisition of novel data from two stages of development with medical imaging in vivo.

DOMEXP project aims to develop research views with several temporal perspectives. First, the project is deliberately focused on the short-term processes that may have occurred during the very first steps of domestication, namely plastic response to captivity. The goal is to provide novel bio-indicators of domestication and life-style changes of animals applicable to archaeological record. Secondly, it is clear that the phenotypic signature of domestication cannot be summarized to plasticity, and that in the long run, selection led to the accumulation of genetic differences characterizing the domestic stocks. It will be crucial to take advantage of the DOMEXP experiment to relate the immediate impact of plastic changes to the phenotypic changes accumulating over generations along with the process of selection. DOMEXP should thus be prolonged by an experiment of artificial selection over three generations, mimicking the steps of domestication subsequent to the breeding in captivity of wild-caught animals.

No publication at this stage of the project

Zooarchaelogists have been trying for a long time to document the early step of animal domestication in the archaeological record but this has been proven a difficult task. Zooarchaeologists use morphological markers based on experiments focused on behavioural selection that led to the genetic divergence of the domestic stock. However, during the very first steps of the domestication process, it is unlikely that such processes already acted to build an observable phenotypic divergence. Another, most often neglected process may nevertheless have played a role in these early steps of domestication: namely plastic, non heritable phenotypic modifications due to changes in life style. How this kind of early response to domestication may have play a role in favouring, and possibly orienting the later genetic differentiation of domestic stocks, is an important issue for both understanding the pace and processes of the domestication process in ancient societies and the evolutionary role of plasticity.

The geometry and inner architecture of limb bones will reflect the biomechanical changes in loading regimes associated with changes in lifestyle and physical activities. Therefore, the reduction of mobility associated with captivity at the onset of domestication should be detectable in the animal bone micro and macrostructure and used as proxy for the early stage of the domestication that can be traced in the archaeological record. Biomechanical analysis has been widely used in the field of physical anthropology to assess the lifestyle of past population but theses have rarely and only partially been investigated with respect to animal domestication. With the rapid advances in high resolution 3D images acquisition, and morphometric techniques to analyse these 3D objects, time has come for zooarchaeology to pursue this promising research avenue in order to identify new anatomical indicators of human control over animals directly applicable to its biological archives.

To investigate the biomechanical consequences on internal and external structure of the skeleton imposed by the captive environment, DOMEXP will use an experimental approach through the creation of the first wild boar (Sus scrofa) farm experiment dedicated to the simulation of the domestication process. Using different experimental treatments and functional constraints (free range, outdoor limited mobility and indoor reduced mobility) morphometric investigation will rely on skeleton markers apt to investigate functional changes caused by a reduction in mobility: limb long bones (femur, tibia, humerus), and tarsal bones (calacaneus, talus), both strongly involved in locomotion and often found complete in archaeological record. The muscular and skeleton changes during the growth of the animals will be captured with in vivo longitudinal 3D CT and MRI scans. The latest advances in 3D biomechanical and geometric morphometric analysis will then capture and decode the signature of lifestyle variation imprinted in the external and internal structural morphology. The experimental characterization of this phenotypic signature will then be used as proxy to infer the life style/behaviour of Neolithic series of Sus scrofa.

This research action will rely on a real multidisciplinary interaction between fields of functional ecology, evolutionary biology, functional skeletal anatomy, and bioarchaology to achieve an original approach towards a better understanding of the early steps of domestication. The results will also contribute to ongoing discussions about the role of developmental plasticity in the evolution of new phenotypes and will provide unique insights into the cause, pace and amount of phenotypic variation that can be achieved when facing radically new environmental conditions.