I'm almost positive it won't. Admittedly I deal with windows PCs but I think the Macs are bios-locked to the cards.
IDK maybe i'm retarded, let me check.
UPDATE: I guess it's not so much that the cards are specifically locked to the board in some fit of apple techno-voodoo, but simply that the cards don't have the drivers available on the device to support it. Theoretically if you had a machine that had the proper drivers, and swapped it out of the PCI-E slot. . . yeah, it might work.
DOUBLE UPDATE: Hmm. it appears that the 7770 has Linux drivers and I know that the mac OSes are traditionally based off Unix. . . I doubt it but would it work with the linux drivers?
I don't know near as much about UEFI or EFI bios to inform you on that front.