It'll develop a huge ego, threaten to go solo and totally raise hell if any brown M&Ms are found in the backstage candy bowl.

As well it should: Fergie's backside is a sizable part of her show, in every sense of the word.

Few singers spend as much time performing with their back to the crowd as this do-it-all diva.

She undulates as if she's trying to writhe out of her skin, as if her joints were coated in ball bearings.

Her message is clear. "I work what I have," she told the crowd at the Mandalay Bay Events Center on Saturday. "And that's what it's all about."

True to her words, few contemporary pop stars are as workmanlike as Fergie.

She's among the most low maintenance, unself-conscious of the current crop of platinum-plus female chart toppers: Beyoncé goes through more costume changes on her way to the john than Fergie does throughout her entire, 90-minute show, and she performs on a largely unadorned stage while wearing very little makeup.

"I'm not clean, I'm not pristine," she announced during her come-as-you-are hit "Glamorous." "I'm no queen, I'm no machine. I still go to Taco Bell, drive through, raw as hell. I don't care. I'm still real."

She flaunts her lack of pretense, while at the same time questioning it.

"Would you still love me if I didn't work out or I didn't change my natural hair color?" she asks her lover on simmering slow jam "All I Got (The Make Up Song)." But what Fergie lacks in visual ostentation she makes up for vocally: her voice is like a little black dress, suitable for just about every occasion.

She's a true child of '80s radio, back when formats weren't so rigidly codified, when hearing Prince's hard funk next to Madonna's self-empowered pop next to a snarling Guns N' Roses tune was pretty much to be expected.

All those influences are palpable in Fergie's live show, much more so than on her recorded output.

She's a true pop changeling, by turns a tough-talking b-girl, a jazz chanteuse who scats to the rhythm and a bawdy rock 'n' roll singer who headbangs like she's in the front row at a Metallica gig.

At Mandalay Bay, she drifted from tropical reggae ("Mary Jane Shoes") to horn-fired ska ("Voodoo") to tough-talking rap kiss-offs ("Pedestal").

In addition to performing a medley of hits from her full-time outfit, pop-rappers The Black Eyed Peas, she tore through a sweaty set of hard rock standards, bellowing through such staples as Led Zeppelin's "Black Dog" and the Rolling Stones' "Start Me Up," where she swished her hips like a cross between Mick Jagger and a runway model, bursting with more 'tude than a grounded teenager.

Even her breakout hit "London Bridges" came fattened with a riff lifted from AC/DC's "You Shook Me All Night Long."

After banging out such full-bodied rock 'n' roll with a loud backing band, including a particularly forceful take on Heart's "Barracuda" that registered like a crowbar to the teeth, Fergie's own hits seemed a little thin sounding by comparison.

But that didn't stop the gray-haired ladies from dancing in the aisles or the little girls perched atop dad's shoulders from shouting along to every word they knew.

This show was a family affair, and it ended with Fergie bringing her mom out on stage and leading the crowd in singing "Happy Birthday" to her.

And at the end of the day, that's Fergie true appeal: her ability to be a pop pin-up and at the same time still seem like one of the gang.

Even if her booty knows better.

Contact reporter Jason Bracelin at jbracelin @reviewjournal.com or (702) 383-0476.