Evolution of mammalian sperm and eggs

Bill Breed | Chris Leigh | Mario Ricci | Steve Cooper

Recent work by PhD student Melissa Bauer and others in our group on arid zone rodents has shown that a few species invariably produce highly pleiomorphic sperm (Bauer & Breed, 2006; Breed et al, 2007), whereas in other species the sperm head develops an elaborate cytoskeleton that appear to be facilitate egg coat binding and penetration at the time of fertilisation (Breed, Idriss, Leigh & Oko, 2009).

Comparative studies on the evolution of egg coat glycoproteins in the Australo-Papuan old endemic rodents have shown that in some lineages the putative sperm combining region has undergone positive selection (Swann, Cooper & Breed, 2007). In marsupial sperm we have shown, in collaboration with an American group, that one of the key protein molecules on the sperm surface involved in egg coat binding is likely to be galactosyltransferase (Braundmeier, Breed & Miller, 2008).