There comes a time in every science writer’s career when one must write about female sea monkeys having sex with male sea monkeys from the future, and the troubles that follow.
That time is now.
A number of experiments suggest that females have to pay a steep price for these male shenanigans. Anti-aphrodisiacs are toxic to the females, shortening their lifetime. Why would males harm the females that carry their offspring? In many species, males can mate with many females. The long-term health of any one female doesn’t matter–in an evolutionary sense–to the male.
As natural selection favors increasingly deadly male mating strategies, this onslaught opens up the opportunity, in turn, for the evolution of counterstrategies in females. In some species, females may evolve antidotes to male poisons. The males, in turn, may evolve counterattacks to overcome these new defenses. Theoretically, this coevolution can become a never-ending cycle of sexual conflict, capable of producing some of nature’s greatest extravagances (like absurdly kinky ducks).
Up till now, the best evidence for this kind of sexual conflict came from experiments. Scientists manipulated Drosophila flies so that the males were free to evolve while the females couldn’t. The result: the lifespan of the females got shorter and shorter over the course of generations. In a flipped version of the experiment, scientists prevented males from mating with lots of females, as they normally do. Instead, the male flies were forced into monogamy. Now there was no evolutionary reward for competing with other males. Over time, the male fly toxins got less toxic, and the females lost their defenses.
If sexual conflict is an ongoing evolutionary process, you’d expect females to fare differently with males from different time periods. They’d be best-adapted to the males of their own time, and worse adapted to males from other times. Evolutionary theorists have developed two different models for how this time-traveling sex would play out. It’s possible that males and females escalate their adaptations over time in an evolutionary arms race. It’s also possible that evolution moves more like a merry-go-round. For a while, one male strategy may dominate, and one female counterstrategy dominates as well. But then a new male strategy pops up, for which the females have no defense at all. That male strategy then rises to dominance, and a corresponding female counterstrategy eventually evolves as well.
Another mystery is how the time-traveling males are harming the females. Rode and his colleagues note one unusual aspect of brine shrimp sex: males and females can stay clasped together for hours–even days. They’re not cuddling in some erotic afterglow. Studies on other species suggest that the males are holding on tight and the females would prefer to get on with their lives. Amplexus, as this embrace is known, may be yet another way for males to outcompete their rivals. By holding on tight to females, they can prevent their mates from finding other males.
Females pay a price for this guarding; it can make them easier targets for predators and prevent them from eating. Scientists have found that female water-striders have evolved lots of acrobatic moves to get clasping males off of them. It’s possible that sea monkeys engage in a similar sexual wrestling match, and that the male and female moves evolve over time.
Whatever the answer to these questions, one thing seems fairly clear. If you’re a female sea monkey, and you see a blinding flash of light, and a male sea monkey suddenly appears saying he’s got to protect you from an army of sea monkey robots from the future–take care. Your well-being is definitely at risk.
