The author(s) declare that they have no competing interests.
All authors designed the study. BBF was responsible for data
acquisition, RK conducted the statistical analyses. BBF, RK, TA and CB
contributed to the interpretation of data, BBF drafted the manuscript
versions, RK, TA and CB revised the drafts critically for important
intellectual content. All authors gave final approval to the version to
The study was supported by grants from the Swiss National Science Foundation (NF Nos. 3200-061906.00 and 3200 BO-102130).