By Lewis Krauskopf, Bansari Mayur Kamdar and Praveen Paramasivam (Reuters) – The benchmark S&P 500 index rose on Monday, boosted by megacap tech and growth stocks and a surge in Twitter after Elon Musk revealed his stake in the company, amid cautionary signals in the bond market and talk of more sanctions against Russia over Ukraine. Defensive sectors, such as utilities and healthcare, lagged. Shares of Twitter surged after Tesla Inc Chief Executive Musk revealed a 9.2% stake in the micro-blogging site, making him its largest shareholder. Shares of other social media companies also rose. Tesla…