UBS ( UBS) said Jerker Johansson has resigned as CEO of the Swiss bank's investment bank and it has appointed Alex Wilmot-Sitwell and Carsten Kengeter as co-CEOs of the unit. Johansson joined UBS in March 2008 and was a member of the bank's group executive board. No reason was provided for his resignation in a statement the bank issued Monday. Wilmot-Sitwell has been the joint global head of UBS's investment banking department since November 2005 and chairman and CEO of UBS Group Europe, Middle East & Africa since January 2008. He is a member of the group executive board. Kengeter is the joint global head of fixed income, currencies and commodities within UBS investment bank. In his new role, Kengeter will be a member of the group executive board. Earlier this month, UBS estimated it would report a first-quarter loss of almost 2 billion Swiss francs and planned to to reduce headcount in 2010 to 67,500 from 76,200 at the end of March. The personnel moves at the investment bank are some of the biggest changes since Oswald Gruebel took over as the bank's CEO in February.