Kathleen Gaffney, a key member of a team that invests $82 billion at Loomis Sayles & Co. in Boston, has quit to work for cross-town rival Eaton Vance Corp.

Gaffney was part of a team working for renowned bond manager Dan Fuss at Loomis Sayles. The group is responsible for about half of all the assets under management at the firm, including the $21.9 billion Loomis Sayles Bond fund.