PM usually makes the call, be it auto/ manual flying. If he miss it, the PF will back him up by calling it( after a period of time). During low vis ops, PM will be monitoring the instruments as well as the a/c therefore it's the PM who will do the callout while the PF will scan in and out. Same rule applies, IF PM miss it PF will back him up by calling it.
My 2 cents worth.