The Swansea centre takes over from the Cardiff hooker Jonathan Humphreys, who has decided not to appeal after receiving a seven-day ban following his sending-off in Sunday's European Cup semi-final defeat at Brive.
Garin Jenkins has been elevated from the replacements bench to play instead of Humphreys. The Swansea hooker wins his 31st cap. Barry Williams, of Neath, is the new replacement hooker.
Wales' coach, Kevin Bowring, said: "I have used this as an opportunity for someone to gain personal development from the situation, rather than go to a tried and trusted captain."
Gibbs has played just three Tests after returning from rugby league with St Helens.
Bowring added: "I have been impressed with Scot's focus, attitude and discipline. His contribution has been impressive since he returned from rugby league - both on and off the field."
Bowring felt that Humphreys had been "very sensible" to drop his appeal against his suspension. The 27-year-old hooker said: "Although bitterly disappointed to be sent off for the first time in my career I have decided not to appeal against the decision.
"As captain of Wales, I am mindful of the need to set an example and will accept the adjudicator's decision, even though it is very painful to take.
"By choosing this route, it allows the Welsh team to prepare without any interruption for the game against the USA and this must be my ultimate concern."
The flanker Ian Smith will miss the opening match of Scotland's Five Nations' Championship after breaking his thumb while playing for Gloucester. Smith had hoped to recover from the injury suffered in a Pilkington Cup game against Leeds last month in time for Scotland's opener against Wales at Murrayfield. But Smith, who has won 20 Scottish caps, had to undergo surgery to pin the broken bone and it will not be removed until the day of Wales match in two weeks' time. It will be the first full Scottish international Smith has missed since the 1995 World Cup finals.
Andy Robinson will combine his Bath playing and coaching roles at least for the remainder of this season. The former England flanker lines up against Anglo-Welsh Cup opponents Swansea tonight, among six Bath internationals on show.
"It is important I maintain my fitness," said Robinson, who on Monday succeeded Brian Ashton as Bath's full-time head coach. "I am needed as cover for our other open-side flanker, Nathan Thomas, and will need to be ready if Nathan got injured."
Courage League Second Division strugglers Moseley are to be docked two points for playing an unregistered player following a dramatic about-turn. Moseley have admitted they made an administrative error by playing lock Andy Freke in their defeat at Bedford in November, while he was still registered with his first club Woodrush. English Professional Rugby Union Clubs Ltd announced two weeks ago they would not punish the Midlands side, but the Rugby Football Union's competition sub-committee have now overruled them.Reuse content