Shares of online brokerages fell sharply on Wednesday, with Interactive Brokers Group dropping more than 7% intraday and Robinhood Markets sliding about 5%. The weakness hit the sector even as the broader equity market took a breather following a morning rally. The pullback came after the S&P 500 briefly notched a record 646 before giving up gains. Market participants pointed to profit-taking and concerns that higher interest rates could weigh on trading activity and margin loans as possible drivers of the move, although no single catalyst emerged.