Funding for this research was provided by:
National Natural Science Foundation of China (41772008)
Fundamental Research Funds for the Central Universities (2652017215)
National Geographic Society (EC0768-15)
Natural Sciences and Engineering Research Council of Canada (2015-00681)
Article History
Received: 17 October 2018
Accepted: 28 November 2018
First Online: 14 December 2018
Competing interests
: The authors declare that they have no competing interests.
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