Prediction gridDifficulty 2/5 · StandardConcept explanationArgumentation

Before or after the zygote?

Biologists studying pairs of closely related species recorded what keeps each pair from exchanging genes in nature. For each case, decide whether the barrier acts before a hybrid zygote forms (prezygotic) or after one has formed (postzygotic).

Classify the reproductive barrier in each case as prezygotic or postzygotic.

Two frog species share the same ponds, but one breeds in early spring and the other in early summer.
Barrier
Horses and donkeys mate and produce healthy mules, but mules almost never produce offspring.
Barrier
Two monkeyflower species grow side by side; one is pollinated by bumblebees, the other by hummingbirds.
Barrier
Eggs of one salamander species fertilised by a related species' sperm stop developing within a few days.
Barrier
Two sea urchin species spawn together, but the sperm of one can't bind to the eggs of the other.
Barrier
Two rice strains give vigorous, fertile first-generation hybrids, but many second-generation plants are weak or sterile.
Barrier

Row	Barrier
Two frog species share the same ponds, but one breeds in early spring and the other in early summer.
Horses and donkeys mate and produce healthy mules, but mules almost never produce offspring.
Two monkeyflower species grow side by side; one is pollinated by bumblebees, the other by hummingbirds.
Eggs of one salamander species fertilised by a related species' sperm stop developing within a few days.
Two sea urchin species spawn together, but the sperm of one can't bind to the eggs of the other.
Two rice strains give vigorous, fertile first-generation hybrids, but many second-generation plants are weak or sterile.

Answer every part to submit.