1. Dept of Biology and Environment, Univ. of Haifa; Oranim Tivon Israel
2. INRA, 400 Route des Chappes, FR-06410 Sophia Antipolis Cedex; France
3. INRIA, Sophia Antipolis, Projet Hephaistos, 2004 Route des Lucioles, BP 93, FR-06902 Sophia Antipolis Cedex; France