London-listed drugmaker Shire Plc (SHP.L) succumbed to an increased 31 billion pounds ($53 billion) takeover offer from Abbvie Inc (ABBN.N) on Monday, signaling the conclusion to a long-running courtship largely motivated by tax. Shire said it was ready to recommend the deal, the latest in a list of mergers proposed by U.S. firms seeking to cut their tax rates, and which comes less than seven weeks after the collapse of Pfizer Inc’s (PFE.N) $118 billion bid for AstraZeneca Plc (AZN.L), also motivated in part by tax factors.