While extremely rare among mammals, so-called semelparity, or suicidal reproduction, is common in nature. Many plants—including all grains, many vegetables, and all plants that live just a year—reproduce this way, as do salmon, insects, and a handful of frogs and lizards.

Just four mammal species are known to reproduce this way, and all are rare insect-eating marsupials. These dads die after devoting all their resources and energy to mating, an effort that helps their sperm—and genes—win out.

Since the 1970s, scientists have suspected that females synchronize mating so that they wean their young at the same time that insect abundance peaks each year. During that shortened, frenzied mating period, competition to mate with the females and methods of doing so are