On Wednesday's edition of Investor Beat, host Alison Southwick and Motley Fool analysts Taylor Muckerman and Jason Moser take investors through the biggest stories from the market today.

When Mary Barra replaces Dan Akerson as CEO of General Motors, she'll make the history books as the first female head of a U.S. automaker. In the lead story from today's Investor Beat, Jason and Taylor talk about the challenges ahead for Barra and discuss the year's best shake-ups in the corner office.

Then the guys look at four stocks making moves on the market today. MasterCard delivers Christmas early for shareholders with a stock buyback and boosted dividend. Discovery Communications eyes acquiring Scripps Network. Costco misses on earnings, but that's not the number to watch. And Joy Global delivers a cringeworthy earnings report.

And finally, our analysts explain why they're keeping close watch on shares of Facebook and Rio Tinto. Should Facebook investors be concerned that Twitter has an edge in the all-important mobile advertising space?

Alison Southwick owns shares of Costco Wholesale. Jason Moser owns shares of Walt Disney, Amazon.com, Coach, and Twitter. Taylor Muckerman has no position in any stocks mentioned. The Motley Fool recommends Amazon.com, American Express, Coach, Costco Wholesale, Discovery Communications, Facebook, Ford, General Motors, MasterCard, Scripps Networks Interactive, Tesla Motors, Visa, and Walt Disney and owns shares of Amazon.com, Coach, Costco Wholesale, Facebook, Ford, MasterCard, Tesla Motors, Visa, and Walt Disney. Try any of our Foolish newsletter services free for 30 days. We Fools don't all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.