Loyalty

Speculation
Loyalty is earned by comeleting missions that are mostlikely to have a great difficulty, and upon comletion the PC recives a large bonus in loyalty from the concerned squadmate and an achievement that ties into the mission's story. For example: "Treason" is awarded for gaining Tali's loyalty. The title may be connected to Tali's banishment from the Migrant Fleet. Or "The Cure", awarded for gaining Mordin's loyalty. In a specific video-preview, Commander Shepard is tasked by Mordin to find a cure to a biological weapon, possibly the genophage if Mordin is the salarian scientist on Tuchanka.