We thank Ivan G. Pola for his laboratory work. We are grateful to Jerónimo de la Hoz for helping with sampling. This study has been financially supported by European Union INTERREG projects 040 (ASAP), 203 (ASAP-2) and AARC. J. L. Hórreo holds a Research Contract funded by the FICYT within the Project IB09-0023. G. Machado-Schiaffino was supported by the EU Framework 7 project SALSEA-Merge. We are grateful to two anonymous GCB reviewers for very helpful comments on this manuscript.