Twitter (TWTR) shares spiked Wednesday on reports co-founder Jack Dorsey will assume the position of permanent CEO. Dorsey has operated as interim chief since June while the social network searched for a permanent replacement. Stocks may have ended the day on a positive note, but the three-month period remained its worst quarter in four years. Since July, the S&P 500 has dropped more than 7%. Western Digital (WDC) was among the best performers on the S&P 500 after China's Unisplendour agreed to a 15% stake worth $3.8 billion. Gap (GPS) fell after president of its Old Navy chain, Stefan Larsson, accepted the CEO position at rival Ralph Lauren (RL). Larsson will take the reins from its namesake founder Ralph Lauren nearly 50 years after he created the label.