The Vanguard Group of Malvern, Pa. is adding a fifth asset manager to its Explorer Fund because of an increase in investor interest in the fund, said John Demming, a company spokesperson.

Investment adviser Grantham, Mayo, Van Otterloo & Co. of Boston will join four other firms April 3 in managing the $4.4 billion small company growth fund.

The new firm will be in charge of all new assets, according to Demming. Currently, assets are divided between Granahan Investment Management of Walthams, Mass. (40 percent), Wellington Management Company of Boston (28 percent), Chartwell Investment Partners of Berwyn, Pa. (14 percent) and Vanguard Core Management Group of Valley Forge, Pa. (10 percent). Approximately seven percent of the fund's assets are held in short-term reserves.

The addition of the new manager will not have a "substantial" impact on the fund's expense ratio, Demming said.

Earlier this month, Vanguard named Grantham, Mayo, Van Otterloo & Co. the investment adviser to its new U.S. Value Fund. The firm filed for the fund March 16.

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