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By Root 341 0

or didn't, and she was there at the time (aside from exceptions such as brood parasitism, which I'll discuss later). In mammals, where the events of mating and birth are even more widely separated, the problem of knowing which babies are sired by which male is even worse. There, of course, only the female can supply the offspring with milk, but males can perform other fatherly acts, for example, protecting everyone from predators or getting food for the mother.

This disparity between the likely payoff to each sex that accrues from devoting oneself to one's offspring is often cited as the sole reason for males rarely being the sex that takes care of the young. It's evolutionary good sense to refuse to take on someone else's genetic investment, and males are generally thought to benefit more by competing for mates than by sticking with the offspring. But while certainty of paternity probably plays some role in the evolution of different reproductive behaviors, it is now emerging that it can't be the whole explanation. It's all very well and good to say that a male "should" go off and seek other females to mate with rather than stick around and care for the ones his current mate produces. But what are his chances of succeeding? Everyone likes to think he could have been a contender, but in reality, it's tough out there. Females may be scarce, they may be unwilling to mate with every philandering male that passes by, and the risk of being eaten by a predator before one is found may be high. Tip the balance of any one of these variables, and the parental care patter can skew toward mom, dad, or both. And insects are perfect test cases for ideas about "innate" parenting roles, because once the eggs are produced, either sex can easily protect or bring food to the babies, unlike mammals, where females have all the milk-producing apparatus.

Single fathers are rare among insects, as they are elsewhere, but when they occur they do a bang-up job. Giant water bugs are true bugs, meaning they have strawlike mouthparts that they use to suck up their food. Some bugs, for example, aphids, merely sip sap, but the giant water bugs are fierce predators that ambush prey such as other invertebrates, fish, salamanders, and frogs. Once they grasp their victim, the bugs inject enzymes that liquefy the contents so that the interior can be extracted. About the size of an almond with the shell on, the bugs patrol lakes and streams around the world.

When it is time to breed, males attract females by suggestively rippling the water's surface. Unlike most insects, after mating, instead of the female taking off with her store of sperm, giant water bug females from most species proceed to lay eggs on the back of the male, where they sit in neat pearly rows until it is time for them to hatch. Although the conspicuous bugs were noticed by early naturalists, the individuals bearing the eggs were assumed to be females. Even when the sex of the brooding individuals was known, scientists as late as 1935 declared that the females must be forcing the males to carry the eggs. The father, however, always mates with the female before allowing her to deposit her eggs, and the pair may go through several rounds of mating followed by egg laying, apparently at the male's behest. This probably ensures that at least a majority of the eggs carried are indeed the male's own. He then solicitously ensures the eggs are supplied with oxygen by periodically raising his back above the surface. Although more than one female can deposit her eggs on a given male, the space on his back may become limited, and the males do what they can to position females so that they lay eggs to fill in any gaps in the row. Carrying around the eggs is no easy task; their combined weight can be twice as heavy as the male himself. In one group of giant water bugs, the females lay egg masses that are attached to vegetation at the water's edge, and the males then guard the eggs while the female departs, perhaps to lay another batch fertilized and protected by another male. The male stays to guard the