SACRAMENTO, Calif. - The unassuming ukulele has gone viral. No longer are the instruments seen as a frivolous novelty. They are popping up all over YouTube - and being strummed in chart-topping hits.

The ukulele, with its relatively tiny size and four strings, could be thought of as a simple instrument, but it has a rich history within the Hawaiian islands. And native Hawaiian Jake Shimabukuro ...