GENETIC DISTINCTIVENESS OF ITALIAN AUROCHS: NEW INSIGHTS INTO CATTLE DOMESTICATION PROCESS

1. GENETIC DISTINCTIVENESS OF ITALIAN AUROCHS: NEW INSIGHTS INTO CATTLE DOMESTICATION PROCESS Giulio Catalano (1),Stefano Mona (2), Martina Lari (1), Paolo Boscato (3), Luca Sineo (4), Antonella Casoli (5), Giorgio Bertorelle (2), David Caramelli (1)* (1)Department of Evolutionary Biology “Leo Pardi”, University of Florence, Florence, (2)Department of Biology and Evolution, University of Ferrara,  Ferrara,  Italy (3)Department of Environmental Sciences, University of Siena, Siena, Italy (4)Department of Animal Biology, University of Palermo, Palermo, Italy (5)Department of General and Inorganic Chemistry, Analitical Chemistry and Physical Chemistry, University of Parma, Parma, Italy *david.caramelli@unifi.it • INTRODUCTION • The hypothesis that cattle were domesticated about 10,000 years ago from wild aurochsen (Bos primigenius) in the Middle-East or Anatolia and in Pakistan implies that all present day European breeds (Bos taurus) descend from Fertile Crescent ancestors. Several molecular studies, mostly based on mtDNA, supported the single origin hypothesis, suggesting small or no contribution from European wild forms to domestic breeds (Troy et. al 2001; Edwards et al. 2007). However, recent findings on both ancient and modern mtDNA (Beja-Pereira et al. 2006; Achilli et al. 2008) suggested a more complex domestication process, at least in Southern Europe. Here we analyse 10 new 120 bp mtDNA control region sequences from the Italian aurochs, and we compare them to published sequences in order to: (i) verify previous insights which suggested a significant role of Palaeolithic aurochs in the domestication process in Europe (Beja-Pereira et al. 2006); (ii) investigate the genetic variability and the demographic history of the Italian aurochs in comparison with the Northern European populations; (iii) study the bias introduced in the analysis of genetic variation when the age of the sequences is not taken into account. The MDS analysis suggests that the Italian aurochs is genetically closer to the European and the Middle Eastern domestic breeds than to the North European aurochs. • METHODS • Median-joining network among aurochs sequences • Multidimensional scaling (MDS) based on a matrix of pairwise Fst values between populations/breeds • Inferences on the demography of the Italian aurochs population (a total of 15 sequences) and of the European aurochs (37 sequences from Edwards et al. 2007) using the software BEAST 1.4.5 with two different coalescence prior models (constant size and exponential • change). • Serial coalescent simulations performed on a grid of Ne and exponential growth rates, assuming a temporal sampling scheme as in the real data. For each scenario, 1,000 replicates were performed and Tajima’s D and Fu’ Fs were used as simple statistics to infer changes in population size. Figure 2. MDS analysis based on pairwise Fst. BPE is North European aurochs; BPI is the Italian aurochs; MOL, LYB, EGB and EGY are African cattle breeds. Table 2. Simulation results. Tajima’s D and Fu’ Fs are computed assuming different combinations of Ne and g (the growth rate). HE refers to sequences sampled at different time points in the past (the age of the sequences analysed in Edwards et al. 2007 were used in the simulations). IS refers to a contemporary sample. Fig 1. Median-joining network of aurochs sequences. The branch length is proportional to the number of substitutions; the node diameter is proportional to the haplotype frequency. The names of the major haplogroups are shown. BEAST revealed that a model with exponential change in populations size was slightly preferred by the Bayes Factor in both the Italian and the North European aurochs. The median values of g suggested a contraction, rather than an expansion (Table 1), but the 95% HPD include zero. The analysis, however, showed poor mixing of the paramenter g, even in long runs. RESULTS The analysis of ten new sequences revealed a much higher variability in the Italian aurochs compared to the North European populations, with a prevalence of the macro-haplogroup T (Figure 1) already found in Beja-Pereira et al. 2006. This is the most common haplogroup in European cattle breeds. This finding seems in contrast with the star-like network (Fig 1) observed for the North European sequences. We performed serial coalescent simulations to determine if an heterochronous sampling could produce a skew in Tajima’s D and Fu’ Fs typical of population expansion. We found that both statistics are skewed toward negative values when the population size is constant but the sequences are sampled at different time points in the past (Table 2). • CONCLUSIONS • Our data suggest that T is the typical haplogroup in the Italian aurochs; P sequences, however, are observed also in Italy, supporting the idea that the genetic variability was higher in Southern Europe compared to Central and Northern Europe. The high genetic similarity between Italian aurochsen and domestic breeds confirms a previous study based only on five sequences (Beja-Pereira et al. 2006). The hypothesis that the domestication history was probably different in Italy (and possibly in Southern Europe) compared to other areas is supported by the new data. • 2. The Bayesian analysis indicates that aurochsen did not undergo a post-glacial expansion. This result is in contrast with the starlike shape of the network in the Northern European group, but we showed that sampling at different time intervals could artificially generate a signal of expansion. Table 1. Demographic parameters estimated by BEAST. Ne is given in thousand of individuals. P and T are coalescence times (in thousand of years) of the two major haplogroups. TMRCA is in thousand of years. Growth rate (g) per generation is multiplied by 10^5. 95% high posterior density (HPD) in parenthesis. BPE is North European aurochs; BPI is the Italian aurochs.