AUTHOR CONTRIBUTIONS
S. Shi and Z. Guo designed and supervised the project. S. Shi, C. Zhong,
X. Li, H. Lyu and N. C. Duke collected the samples. Z. Wang and H. Lyu
produced the data. Z. Wang and Z. Guo analyzed the data. Z. Guo and Z.
Wang wrote the manuscript. S. Shi and N. C. Duke helped in improving the
manuscript. All the authors read and approved the final manuscript.