Acknowledgments: Many thanks to Dana Wilson, Susan Hay, David Brown and Vivienne Buchan at RINH, Siegrid Hilken and Esther Lipokatic-Takacs at UVMH for the excellent technical support and advice provided. Many thanks are due to Claus Mayer of Biomathematics, Statistics Scotland for assistance with the statistical analysis of data. Author Contributions: Conceived and designed the experiments: IP SS FS PB. Performed the experiments: IP RD FS. Analyzed the data: IP RD FS SS PB. Wrote the paper: PB SS FS IP.Peer reviewedPublisher PD