1. Institute of Zoology, Chinese Academy of Sciences, Box 56, Beijing 100080, China
2. Laboratory of Visual Information Processing, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China
3. School of Biological Sciences, University of Bristol, Woodland Road, Bristol BS8 1UG, U.K.
4. Department of Physiological Science, UCLA, 621 Charles E. Young Drive S., Los Angeles, CA 90095–1606, U.S.A.
5. College of Life Sciences, Guangxi Normal University, 541004, Guilin, China