Phylogenetic relationships of Argentinean Creole horses and other South American and Spanish breeds inferred from mitochondrial DNA sequences P. M. Mirol*, P. Peral Garcı´a*, J. L. Vega-Pla † and F. N. Dulout* *CIGEBA, Facultad de Ciencias Veterinarias, Universidad Nacional de La Plata, La Plata, Argentina. † Laboratorio de Grupos Sanguı ´neos, Servicio de Cria Caballar, Co ´ rdoba, Spain Summary South American horses constitute a direct remnant of the Iberian horses brought to the New World by the Spanish conquerors. The source of the original horses was Spain, and it is generally assumed that the animals belonged to the Andalusian, Spanish Celtic, Barb or Arabian breeds. In order to establish the relationship between Argen- tinean and Spanish horses, a portion of the mitochondrial D-loop of 104 animals belonging to nine South American and Spanish breeds was analysed using SSCP and DNA sequencing. The variability found both within and between breeds was very high. There were 61 polymorphic positions, representing 16% of the total sequence obtained. The mean divergence between a pair of sequences was 2.8%. Argentinean Creole horses shared two haplotypes with the Peruvian Paso from Argentina, and the com- monest haplotype of the Creole horses is identical to one of the Andalusian horses. Even when there was substantial subdivision between breeds with highly significant Wright’s Fixation Index (FST), the parsimony and distance-based phylogenetic ana- lyses failed to show monophyletic groups and there was no clear relationship in the trees between the South American and any of the other horses analysed. Although this result could be interpreted as mixed ancestry of the South American breeds with respect to the Spanish breeds, it is probably indicating the retention of very ancient maternal lineages in the breeds analysed. Keywords D-loop, horse, mtDNA, phylogeny. Introduction The Argentinean Creole horse constitutes a direct remnant of the Iberian horses brought to the New World by the Spanish conquerors during the 15th century. The source of the original horses was Spain, and this was at a time when the Spanish horse was being used for improvement of horse breeding throughout Europe. On the basis of historical records, at least 250 horses where shipped to the continent, from the second voyage of Columbus in 1493 to Nun ˜ez de Cabeza’s trip in 1540 (Rodero et al. 1992). These horses, as all other domestic animals transported, were quickly dis- persed and became very well adapted to the new environ- ment. At that time, Spanish exports arrived directly from the ports of Spain to their final destination, with a stop on the Canary Islands or the Antilles. There were in Spain three main morphological equine types: the Celtic type of tarpanic origin in the north and west region of the penin- sula; the Spanish type, descendent from the African Barb horse, in the south and east; and finally, in the central area, the hybrid between both of them. As Seville, Cadiz and other southern ports monopolized the navigation to America, it could be assumed that horses taken to America were mainly of the Spanish type or Andalusian (Rodero et al. 1992). Address for correspondence P. M. Mirol, School of Biological Sciences, Queen Mary, University of London, Mile End Road, London E1 4NS, UK. E-mail: p.m.mirol@qmul.ac.uk Accepted for publication 29 March 2002 Ó 2002 International Society for Animal Genetics, Animal Genetics, 33, 356–363