ORLANDO, FLA. — Darden Restaurants, Inc., one of the world’s largest full-service restaurant operators, has retained global executive search firm Russell Reynolds Associates to assist the company in the recruiting of its next chief executive officer. Clarence Otis is stepping down as chairman and c.e.o. no later than Dec. 31. To ensure a smooth transition, Charles A. Ledsinger Jr. has been appointed independent non-executive chairman of the board.