What is the typical mode of fertilization in sticklebacks during reproduction?

• A. External fertilization; females lay eggs in a male-built nest and the male releases sperm over them.
• B. Internal fertilization
• C. Parthenogenesis
• D. Fertilization occurs in the female reproductive tract

Answer: (A)

Sticklebacks reproduce through external fertilization. The male builds and guards a nest, the female lays eggs into that nest, and the male releases sperm over the eggs in the surrounding water to fertilize them. This water-based fertilization with active male parental care is characteristic of these fish. Internal fertilization would require sperm meeting an egg inside the female’s reproductive tract, which isn’t how sticklebacks reproduce; parthenogenesis (asexual reproduction) isn’t typical for them; and saying fertilization occurs in the female reproductive tract describes internal fertilization, not the stickleback pattern.