Gene expression can be modulated by epigenetic modifications, which may lead to a rapid adaptation to environmental stress. After stress cessation, changes in gene expression could be reversed, which would allow organisms to maintain their phenotype under transient environments, but this mechanism is poorly understood. Social stress downregulates a gene directly involved in pheomelanin synthesis (Slc7a11) by changing DNA m5C levels, avoiding cellular damage caused by stress.

The Retuerta horse is mainly located in the Doñana National Park, specifically in the Doñana Biological Reserve, and in the Guadiamar Reserve. It counts with an approximate population of 300 horses. This specimen was used in the past by the people of Doñana as a work animal and as a means of transport, but, nowadays, this animal lives in the wild. In 2003, the population was sampled and its genetic profile and genetic distances facing other breeds were established. The genetic distance tree...