Division of Biology, California Institute of Technology, Pasadena, CA 91125, USA. vanauken@caltech.edu|Division of Biology, California Institute of Technology, Pasadena, CA 91125, USA. vanauken@caltech.edu|Division of Biology, California Institute of Technology, Pasadena, CA 91125, USA. vanauken@caltech.edu|Division of Biology, California Institute of Technology, Pasadena, CA 91125, USA. vanauken@caltech.edu|Division of Biology, California Institute of Technology, Pasadena, CA 91125, USA. vanauken@caltech.edu