SC acknowledges a PhD grant from the Italian Ministry for
University and Research, MIUR. DM benefited of a grant for visiting
professors funded by the University of the Balearic Islands. LML
was supported by the Campus de Excelencia Internacional Program
(Ministerio de Educación, Cultura y Deportes). Sample collection
was carried out in the frame of the Project EHRE (CTM2009-
08270/MAR, Spanish CICYT). We are grateful to Antonio TovarSánchez,
Ana Massanet and David Sánchez-Quilez for sample
collection. DM gratefully acknowledges Mr. S. Grigioni from the
mechanical workshop of the University of Insubria.