During mating, a male frog clasps a female and releases sperm while she deposits eggs in the water. A male larger than its female mate fertilized significantly fewer eggs, because he was not in proper position for the sperm to reach all of them. Males smaller than the optimal size did not have an adequate sperm supply to fertilize all of the eggs. So to maximize egg fertilization and have the highest reproductive success, a female needs a mate of the proper size, about 80 percent her size. However, the males have their own agenda.
Larger males can physically displace smaller ones chosen by the female.
Thus, a larger one ends up mating with her instead. These bullies of the frog world fertilize a lower percentage of the female's eggs. But they produce more of their own offspring, and pass on more of their own genes, than if they had not mated at all. Smaller male frogs sometimes successfully mate by being sneaky. When a male gives a mating call to attract the female, a smaller male may remain quiet, but ever alert for an approaching female.