The Wiggles -- clockwise from top left, Murray Cook, Sam Moran, Anthony Field and Jeff Fatt -- will perform at 6:30 p.m. today at the Thomas & Mack Center.

Losing one member of a popular music group can upset the group's chemistry, not to mention create a lengthy period of adjustment.

But that wasn't the case when Greg Page of the Wiggles retired from the Australian children's music group -- his understudy, Sam Moran, quickly donned Page's yellow shirt and it was business as usual.

The Wiggles perform their "Racing to the Rainbow Live!" show today at the Thomas & Mack Center.

Page dropped out of the group in November 2006 after being diagnosed with orthostatic intolerance, a chronic illness affecting a person's blood flow, heart rate and blood pressure.

Moran had been Page's understudy for four years and had taken Page's place for 150 shows. He also had met the group nine years ago when he was performing in a musical by John Field, the brother of Wiggles star Anthony Field (he's the one in the blue shirt).

Reaction to the new Wiggle has been varied, says Moran, who originally trained as an opera singer. "I've been amazed at how children have accepted me. If you explain to them up front, they're open to change. Sometimes more so than adults."

Moran says there had been warning signs that Page was becoming ill as much as three or four years ago.

"We had no idea what it was," he says. "His condition is notoriously hard to diagnose. He'd have a dizzy spell five minutes before going on and I'd have to quickly get in costume. But he's been able to see the silver lining. He's able to spend more time with his children."

While Moran has blended in well with the rest of the Wiggles -- Murray Cook (red shirt), Jeff Fatt (purple shirt) and Field -- he admits his voice is "a little different than Greg's. I've been filling in for such a long time, though, that there's not too much of a difference now. We've only had to change a couple of songs."

The group has been touring the United States for only four weeks now, and so far, so good, Moran says.

"We keep it pretty fun on the road. We try to make each show a little different. With kids in the audience, you never know what they're going to say. They even ask for songs we don't sing."

Las Vegas has been good to Moran: Four years ago he met Lyn Stuckey, a choreographer and dancer in the show, here, and they married four months ago.

They have been able to stay close because they're on the road together.

"There will come a time in the future when we won't be together," he says, after they have children. "The others in the group have already made that sacrifice."