About the Authors
Department of Biology, University of York, Heslington, York, United Kingdom
Sainsbury Laboratory, University of Cambridge, Cambridge, United Kingdom
The authors have declared that no competing interests exist.
The author(s) have made the following declarations about their contributions: Conceived and designed the experiments: OL NS CT. Performed the experiments: NS CT. Analyzed the data: OL NS CT. Contributed reagents/materials/analysis tools: OL NS CT. Wrote the paper: OL NS CT.