1. P. Convey is with the British Antarctic Survey, Natural Environment Research Council, High Cross, Madingley Road, Cambridge CB3 0ET, UK.(P.C.)
2. M. I. Stevens is in the Allan Wilson Centre for Molecular Ecology and Evolution, Institute of Molecular BioSciences, Massey University, Private Bag 11-222, Palmerston North, New Zealand.(M.I.S.)