**Acknowledgements**

The author thanks W.O. Dawson, S. Gowda, B. Belliure-Ferrer and B. Sabater for critically reviewing this manuscript. Likewise, the author is grateful to Drs A. Urbaneja, A. Hermoso de Mendoza and S. Foliminova for kindly provide the pictures included in Figures 1 and 7. This book chapter was financed by ValGenetics.
