STORY: U.S. stocks ended lower on Monday, with the Dow dropping half a percent, the S&P 500 shedding more than a third of a percent and the tech-heavy Nasdaq losing half a percent.Many heavyweight tech stocks retreated from last week's gains that had pushed the S&P 500 to record highs.Melissa Brown is managing director of investment decision research at SimCorp."We've had a mini rally, or maybe re-rally, in some of the Magnificent Seven stocks over the last few days, and I think it's just, you know, profit taking. You always see a volume dip at this time of year and, so you know, when you get that kind of strength or weakness on lower volume, it's not particularly surprising to see that any given trade maybe has a bigger impact on the stock when the volume is lower, compared to when the volume is higher."AI heavyweights Nvidia and Palantir both closed lower on Monday.Shares of Tesla dropped more than 3% after hitting a record high last week.Among other movers, bank stocks retreated after a strong rally this year, with Citigroup, JPMorgan Chase and Bank of America all ending lower.On the flip side, energy stocks gained, tracking a 2% rise in oil prices, with Expand Energy and Coterra Energy edging higher.