Nigeria’s currency plummeted more than 40% against the dollar on Monday, the latest sign that low crude-oil prices continue to disrupt the economies of some major oil-producing nations. The steep losses in the Nigerian naira came on the first day of trading since the central bank ended its currency peg to the U.S. currency. Nigeria introduced the fixed-currency regime a few years ago in an effort to stabilize the naira. Since the end of 2014, the country has spent about 20% of its foreign reserves to defend the peg. Reserves fell to $26.5 billion in May, the lowest level in more than a decade, according to the central bank’s figures. Weaker revenue from low oil prices convinced the government it could no longer continue spending the dollars needed to maintain the fixed rate, analysts say. Oil prices plunged about 75% between mid-2014 and early this year. While crude prices […]