Final answer:
Cryptic female choice is the method not used by male animals to guarantee paternity; it's a strategy where females may influence which sperm fertilizes their eggs, distinct from male-dominated paternity assurance methods like sperm competition, mate guarding, and parental care.
Step-by-step explanation:
The method used by a male animal that is NOT a device or method to guarantee paternity is Cryptic female choice. This term refers to a situation where the female of the species has some control over which male's sperm will fertilize her eggs after mating. This is distinct from strategies like sperm competition, where males compete after mating occurs through the quantity or quality of their sperm; mate guarding, where males directly prevent other males from mating with a receptive female; and parental care, which ensures the survival of the male's offspring, thereby indirectly ensuring paternity.
The various mechanisms males use to ensure paternity relate to different mating systems and strategies. In populations with scarce females, such as those with monogamous systems, males may remain paired with a single female through mate guarding or assisting in parental care, leading to increased offspring survival and ensuring their genetic contribution to the next generation.
In contrast, Cryptic female choice allows females to have a say in the paternity of their offspring, potentially counteracting the male strategies.