The males in all 12 species of the marsupial mammal antechinus die after their first time successfully breeding, typically from stressing themselves out. Seriously: the stress of the breeding season destroys their immune system, leading to liver infections and parasites of the blood and intestine. While some females live to breed for another season, all the males are sure to die. That's not the only place males get the short end of the stick: as babies they're denied adequate milk by their mothers, who prefer to wean the females. At least they get to end their pathetic, year-long lives trying to mate with as many females as they can, "in violent, frenetic encounters that can each last up to 14 hours."