Corvak’s Challenge by Ruby Dixon

When the clone pods were abandoned on the ice planet, two of them opened before the others. Corvak, a gladiator and a splice, ran into the snows. He carried Aidy, a confused human woman. They’re on the run, determined not to get caught.
Aidy has no idea what’s going on or why she’s been dumped in the icy mountains. Corvak, however, is convinced this is all one big gladiator game, and one he’s determined to win. To do that, they’ll have to avoid all the others and survive by any means possible.

Why do they need this parasite anyhow…and why do their chests keep humming?