text: Members of the RMT union will walk out at 11:00 BST on 26 April and at the same time on 10 and 12 May.
  The union is against plans for a new grade of on-board supervisor and proposals for drivers to operate doors.
  Govia Thameslink said there would be no job losses or cuts in salary and the changes would make staff more visible.
  Members of the union were 306 in favour of walkouts and 14 against. A total of 320 votes to one backed other forms of industrial action.
  The RMT said it was fighting to keep the conductor grade and the changes were "nothing short of bullying and harassment".
  RMT general secretary Mick Cash said the "reward" for the "loyal and professional service" of members was having their "role and responsibility reduced and their hard-earned terms and conditions attacked".
  "These trains are desperately over-crowded and the conductors are the eyes and ears preventing a major tragedy on the platforms and carriages," he said.
  He added the company had already axed catering services, "threatened" ticket offices and delivered "appalling levels of customer service in their drive to milk these routes for every penny they can".
  A spokesman for Southern, which is run by Govia Thameslink, described any possible strike action as "unnecessary and damaging".
  He added: "The changes we are making to the conductor role mean there will be no job losses and no reduction in salary for any staff, whilst passengers will benefit from having more visible staff on trains.
  "We are preparing contingency plans in case a strike does go ahead, but in the meantime we urge the RMT to return to the negotiating table."
  Southern operates in Sussex, Surrey and parts of Kent and Hampshire.
target: Conductors on Southern railway are to stage three 24-hour strikes in a dispute over changes to their role and the introduction of driver-only trains.