Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, PA 15213, USA.|Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, PA 15213, USA.|Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, PA 15213, USA.|School of Biology, University of St. Andrews, St. Andrews, Fife KY16 9TH, UK.|Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, PA 15213, USA.