About the Authors

Andrew T. McDonald


Affiliation Department of Earth and Environmental Science, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America

Competing Interests

The author has declared that no competing interests exist.

Author Contributions

Conceived and designed the experiments: ATM. Performed the experiments: ATM. Analyzed the data: ATM. Contributed reagents/materials/analysis tools: ATM. Wrote the paper: ATM.