Just weeks since Modern Warfare 3 became the biggest-selling game of 2011, talk about the next in the Call Of Duty series is already heating up.  Call of Duty: World At War and Black Ops developer Treyarch is stepping up development for what will be the ninth title in the franchise. Various job listings have been spotted on the studio's official website, citing applicants should be, amongst other things, “an expert on recent first-person shooters”.