1. Neurobiology and Genetics, Theodor-Boveri-Institute, Biocenter; University of Würzburg; Würzburg D-97074 Germany
2. Animal Physiology, Department of Biology; Philipps-University Marburg; Marburg D-35032 Germany
3. Department of Biology and Geosciences, Graduate School of Science; Osaka City University; Osaka 558-8585 Japan
4. Department of Natural Sciences; Kawasaki Medical School; Kurashiki 701-0192 Japan