Iberian pigs. Image: Carlos Urbino/Wikipedia.It is thought that pig domestication happened first time during the Neolithic, in the Fertile Crescent, a territory around the rivers Tigris, Euphrates, where Mesopotamia and Egipt. From there, pig domestication would spread through the continent. How this selective pressure of domestication affected pig evolution?A new study, published in Heredity, sheds new light on evolutionary aspects of pig species, and particularly on that of the Iberian breed, considered to be representative of original European Mediterranean populations. The study has been led by Miguel Pérez-Enciso, ICREA researcher at Universitat Autònoma de Barcelona (UAB) and at the Centre for Research in Agrigenomics (CRAG). Researchers from the Institute of Evolutionary Biology (CSIC-Pompeu Fabra University) and the National Centre for Genome Analysis (CNAG) also have participated in the study.
The sample dates approximately from the years 1520 to 1550 and is previous to the introduction of Asian pigs in Europe, which were later crossed with local European breeds which are the origin of today's international pig species. The sample pig is contemporary with the beginning of America's colonization. It is not a very old one, but it is an important first step with which we have demonstrated, says Carles Laueza-Fox, CSIC researcher at the IBE, that “it is possible to obtain genome data from these ancient samples”. This is the first time that genomic data of an ancient farm animal are obtained.
“Although it is a very fragmented sample, the gene sequence offers very interesting information", Miguel Pérez-Enciso says. "First of all, we know it is not a white pig because it is missing a duplicated KIT gene which would make it this colour. This coincides with the majority of paintings from that period, in which the animal was always painted black or in reddish tones. We were also able to establish that it is very closely related to today's Iberian pig species, and specifically to the 'Lampiño del Guadiana' strain. We could say that the Iberian pig is very similar to the pigs, which existed in the sixteenth century and no great changes have been registered in this genome. Therefore, more studies will be needed before we are able to distinguish the modern species from the older ones”.
The study indicates that the pig was a domestic pig, given that the sequence presents a series of markers typical of domestic pigs and which are very rare or absent in wild boars (the precursor animals to the domestic pig); moreover, this coincides with the historical registers of the castle, which clearly indicates that pig breeding was an important castle activity. Nevertheless, there is also evidence of occasional crossbreeding between wild boars and ancient pigs, as has happened between wild boars and Iberian pigs.
Applications and future of the research
Oscar Ramírez, a scientist at the Instituto de Biología Evolutiva (IBE), explains: “The genomic data obtained doesn’t cover all the genome, as the sample was small and contaminated by bacteria, which made very hard the sequentation process. Nevertheless, we obtained enough information to compare the data with the genomes of 'Creole' and Iberian pigs and we have seen that the pig from Montsoriu is more similar to the Iberian pig than to ‘Creole’ pig.
The so called ‘Creole’ pigs are presumably the descendants of the animals brought to America by Spanish colonizers, so both should have some similarities. But researchers have demonstrated that this hypothesis is incorrect and that there is very little remaining of those first Spanish animals in today’s 'Creole' pigs, which were crossbred mainly with international pig breeds.
Scientists know that during the domestication process of the pig, crossings between domestic and wild pigs happened occasionally. This research line, says Carles Lalueza-Fox, “will help to find out which traits appeared during the process of pig domestication, how they evolve and which characteristics are the first to appear.” Interest genes could be found, such the ones related to disease resistance or physical characteristics. “The idea is to keep sequencing, in the future, more ancient samples. There are enough samples and very old, some of them from early Neolithic”.
Genome data from a sixteenth century pig illuminate modern breed relationships. O Ramírez, W Burgos-Paz et al. Heredity. http://www.nature.com/hdy/journal/vaop/ncurrent/full/hdy201481a.html