Tier two nations closing gap on top countries, says Wales’s Luke Charteris

• Wales play Japan in Cardiff on Saturday• ‘We know it will be tough against Japan, with their high tempo’A tour of Europe by the southern hemisphere superpowers often generates talk of the gap between north and south, but with this month’s score 3-2 in favour of the four home unions the Wales lock Luke Charteris believes the debate has changed.“There are gaps in the southern hemisphere,” the Bath second-row said. “New Zealand are significantly ahead of South Africa and Australia and the task for the rest of the world is to catch them up. Ireland have shown that beating New Zealand is doable a…