[1] Univ Sussex, Sch Life Sci, John Maynard Smith Bldg, Brighton BN1 9QG, E Sussex, England
[2] Univ London, Royal Vet Coll, Struct & Mot Lab, Hatfield AL9 7TA, Herts, England
[3] Lund Univ, Dept Biol, Ecol Bldg, SE-22362 Lund, Sweden
[4] Francis Crick Inst, Lincolns Inn Fields Lab 44, London WC2A 3PX, England