Authors’ contributions
LZ, HZ and YH conceived the idea. LJ, ZG and DW performed the experiments. LJ, SY, CL and WD performed the statistical analyses. GZ, YX, RW, GL and HW collected the samples. AZ, YH, HZ, LZ and TY wrote the first draft of the manuscript. LJ, SY, CL, BL and L.Z. contributed substantially to revisions. LJ, SY and CL equally contributed to this work. All authors have read and approved the final manuscript.