Geography of surnames in the Azores: specificity and spatial distribution analysis.

In order to obtain a better understanding of the genetic structure of the Azorean population, a specificity and spatial distribution analysis was performed, based on 2,454 different surnames present in the Azorean telephone directory (2002). We considered as specific surnames those with an absolute frequency ratio equal to or higher than 50%. The results revealed 51 specific surnames in the whole archipelago. The smallest island presents the only surname with 100% specificity (Pedras). In addition, São Miguel island, which contains 54% of the Azorean population, has the highest number of specific surnames (25 specific surnames). The spatial distribution analysis was used to detect genetic similarity between municipalities through the calculation of spatial autocorrelation (Moran's I coefficient). Of 240 surnames included in the analysis, 113 showed statistically significant patterns. Five different patterns were obtained, of which the most relevant was isolation by distance and depression (41.6%). However, 43.4% had no defined pattern. The overall correlogram shows a majority of positive values for distances lower than 49 km and between 269-309 km, indicating high similarity between closer municipalities and between distant municipalities whose populations show historic and sociocultural affinities. In conclusion, our data are in agreement with the historical background of the Azorean population.