Alice and Bob are Starfish Aliens that can reproduce asexually as well as sexually.
Inverted: Alice and Bob are just two members of Earth's large population, which is reaching the tipping point.
Subverted: Alice and Bob find other fertile adults
Double Subverted: But not enough of them to maintain a genetically-diverse enough population for more than a couple of generations.
Deconstructed: Two people cannot repopulate (or populate) a whole planet. There needs to be a sufficient number of non-related fertile adults to accomplish this and ensure the long-term survival of the species. Plus there could be squabbles over who gets to mate with whom and when depending on the male-to-female ratio and how marriage and relationships are handled (if they're handled.)
Reconstructed: Alice and Bob and the others (if there are any) find a way to overcome the DNA issue...or just make the best of their time if that's not an option.
Parodied: Adam and Steve are the only survivors...and must figure out this whole Homosexual Reproduction thing.
Zig Zagged: The population fluctuates between too many fertile, non-related adults, just enough of them, and not enough of them throughout history.
Lampshaded: "Is anyone else out there?"
Averted:
Alice and Bob have plenty of potential mates to choose from.
Alice and Bob were wiped out along with everyone else.