Variation and molecular evolution of the sheep oxytocin receptor gene Paré, P¹; Vargas-Pinilla, P²; Paixão-Côrtes, V²;Salzano, FM²; Bortolini,MC²; Henkes, LE¹ ¹Laboratório de Genética e Biologia Molecular, Universidade Federal do Pampa, Uruguaiana, RS. ²Departamento de Genética, Instituto de Biociências, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS. pamela_pare@hotmail.com INTRODUCTION The oxytocin receptor (OXTR) is involved in a range of physiological processes and behaviors, such as the formation of social bonds and milk ejection in mammals. These activities are mediated through interaction with the nonapeptide oxytocin (OXT) and its receptor (OXTR). Recently, this ligand-receptor complex has been investigated in animals of economic interest, since inappropriate behavior and stress can have consequences in meat quality and milk production. Considering that OXT is highly conserved in mammals, OXTR could play a major role in the plasticity of the ligand-receptor system. In Silico data † MATERIAL AND METHODS OXTR reference sequence HM856597.1 of the Ovis aries was compared with those of 22 other placental mammals. † The sequences were aligned and compared using Mega 5.05 software, while DNAsp was used to test neutrality deviations * Original data * A total of 1644 base pairs (bp) were obtained from the DNA of animals of three sheep breeds: Crioula Lanada (N=35), Ile de France (N=6) and Ideal (N=5). * OXTR sequencing in the Ovis aries species * HKA Molecular Evolution To check whether the variations found in all placental mammals tested could be explained by selection or neutrality, the Maximum Likelihood test, NSsites (PAML 4.6) was employed. † Fu and Li’s F* Ka/Ks McDonalds and Kreitman RESULTS AND CONCLUSIONS The Ovis aries OXTR reference sequence indicated that sheep has 6 sites that are uniformly different from cow, pig, horse and dolphin; additionally intraspecific variation (2 synonymous and 3 non-synonymous) mutations were also observed in Ovis aries. Low Ka/Ks values and a lack of significance in McDonalds and Kreitman (p= 0.15647), and Fu and Li's F* tests (intraspecific, p= 0.60126; with outgroup, p= 0.46806) suggest that purifying selection is acting, conserving the OXTR sequence among sheep breeds. The ω average rate for the 23 mammals are smaller than 1 (dN/dS =0.0084; M1a), indicating that purifying selection is also the main factor in OXTR gene molecular evolution, at least in the Eutheria group. It should be remembered, that OXTR is the only specific OXT receptor, which may determine an important evolutionary constraint. Financial Support: