In the evolutionary process, there is often more than one way to accomplish the same task. As biologists continue to study systems in which mating success seems to be determined by the outcome of male-male competition, they're discovering some interesting alternative male strategies. One example is the sneaky strategy. Scientists speculate that the sneaky strategy is a way for younger males to have some chance of reproductive success before they get old enough to bark with the big dogs.
Males that use the sneaky strategy avoid direct conflict and try to mate with females while the other males are busy bashing their horns together or otherwise carrying on. It's not clear how common this phenomenon is, but it's been seen in several species, including frogs and red deer. It's also not clear how successful this strategy is compared with the strategy of the dominant male. For males that would be unable to win physical contests, however, it provides the only chance to contribute genes to the next generation.
The Battle of the Sexes: Male-Female Conflict
In a monogamous species in which males and females enter into long-term reproductive relationships, parents will have an interest in each other's survival because only through the survival of their partners will they be able to produce any offspring. The situation is much different for species with short-lived or no pair bonds. In this case, selection can favor traits of one individual in the pair even if they decrease the partner's fitness.
Several adaptations seem to facilitate the sneaky strategy. One good example occurs in Atlantic salmon. In this species, larger, dominant males guard females and then fertilize their eggs externally as soon as the eggs are laid. The dominant male chases away smaller males that attempt to approach the female he's guarding. The smaller males can't get as close to the female as the dominant male can, but they have an interesting characteristic that may serve to increase their chances of fertilizing at least some of the female's eggs.
Matthew Gage and coworkers found that smaller males' sperm swim faster and can survive longer in the water than those of larger males. Smaller males also produce sperm with different characteristics from those of the dominant males, and these sperm may have a better chance of reaching the female's eggs.
Parents have an interest in providing for the survival of their offspring. From a strictly evolutionary point of view, they don't necessarily have any interest in each other's survival. Why? Because from a fitness perspective, it's better for a male if his partner makes only a few offspring, all of which are his, than if she makes very many offspring that aren't his. The female's fitness is increased by adaptations that favor her reproductive output over that of her mate's. The result of the conflicting goals is an evolutionary version of the battle of the sexes.
The following sections discuss some of the ways this conflict manifests itself in the animal kingdom.
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