WordNet (r) 3.0 (2006):

take turns
    v 1: do something in turns; "We take turns on the night shift"
         [syn: alternate, take turns]

Moby Thesaurus II by Grady Ward, 1.0:

20 Moby Thesaurus words for "take turns":
   alternate, cover, do a hitch, do a stint, do a tour, do time,
   enlist, fill in for, have a go, have tenure, hold office,
   keep a watch, re-up, reenlist, relieve, serve time, sign up, spell,
   spell off, time off