1 Department of Ecological and Evolutionary Biology, Princeton University, Princeton, NJ, USA; Office of Population Research, Princeton University, Princeton, NJ, USA. Electronic address: cmetcalf@princeton.edu.
2 Brigham & Women's Hospital, Harvard University, Boston, MA, USA.
3 Department of Ecological and Evolutionary Biology, Princeton University, Princeton, NJ, USA; Office of Population Research, Princeton University, Princeton, NJ, USA.