Sex with someone from the future can be hazardous to your health

By Carl Zimmer | June 16, 2011 12:24 pm

Michael Biehn and Linda HamiltonThere 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.

In many species of animals, males and females have a conflict of evolutionary interests. Males compete with each other for the opportunity to fertilize the eggs of females. Males use all sorts of strategies in these competitions. They fight with each other for territory, they scare off intruding males, they put scrapers into females to dump out the sperm from previous males, and they inject “anti-aphrodiasiacs” to make females unreceptive to other males.

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.

Now Nicolas Rode of the the Center for Functional and Evolutionary Ecology in Montpellier, France, and his colleagues have found a new way testing this hypothesis: by having males travel through time to mate with females.

The time-traveling males in this case are brine shrimp (a k a sea monkeys). Brine shrimp produce tough eggs that can survive through droughts for years and then hatch into healthy young when water returns. In the Great Salt Lake in Utah, the brine shrimp egg cysts form layers on the lake bed going back decades. Rode and his colleagues gathered cysts from layers that formed in 1985, 1996, and 2007. They brought the cysts back to their lab and reared the sea monkeys. And then they orchestrated some sea monkey sex. They had females mate with males from their own time, as well as from the other years. For example, females from 1996 could mate with males from 2007 and 1985.

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.

Rode and his colleagues tracked the females, noting how  many eggs they had and how long they lived. And they discovered, as predicted, that having sex with males from another time is bad for a sea monkey’s health. The further away in time the sea monkeys were, the sooner the female sea monkey died. When the male traveled 22 years to mate with a female, her life was cut short on average by 12%.

There are lots of caveats to this study–which you’d expect for the first study of its kind. The results weren’t clear enough for the scientists to pick the arms race or merry-go-round model as the best explanation for the conflict between the sexes. And over the entire lifetime of the female sea monkeys, time-shifting didn’t have a measurable effect on their reproductive success. That’s because they females who were dying faster also produced eggs at a faster rate.

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.

Reference: Nicolas O. Rode, Anne Charmantier, Thomas Lenormand. Male-female coevolution in the wild: evidence from a time series in Artemia franciscana” Evolution: in press. DOI: 10.1111/j.1558-5646.2011.01384.x

[Image: Fanpix. Backstory for those who’ve never heard of Kyle Reese]

[Updated to clarify the nature of sea monkey time travel and correct Marseilles to Montpellier]

CATEGORIZED UNDER: Evolution, Top posts

Comments (22)

  1. Were all other environmental factors ruled out, i.e., males from a later time period having more environmental contaminants in their bodies (pollutants, insecticides, etc) to which females from an earlier period might have reduced tolerance?

  2. That wouldn’t explain how the time-travel effect works if the male comes from the future and if he comes from the past.

  3. Luigi

    Would 20 years be enough for visible evolutionary behavior to change the way these eukaryotes mate? When taking into consideration the evolutionary experiment with bacteria, which divide at a much higher rate, this would be very unlikely I think.

    [CZ: Luigi–The shrimp spanned 160 generations in this study. The lab experiments I described in my post on flies got measurable evolutionary changes in far fewer generations.]

  4. Luigi

    Thanks for the reply. I understand, I am assuming that the toxic chemical used as anti-aphrodisiac is brought about by mutations which increase toxicity, favouring the males secreting it, but up to a certain level which does not sufficiently damage the female, correct?

  5. This doesn’t bode well for those people who have opted to be frozen via cryogenic processing.

  6. Luigi

    @Chris. Its interesting to apply this idea to humans. In my opinion, since the major populations have practiced monogamy, every individual has approximately an equal chance of producing offspring and passing on his genes, therefore it seems we have stopped evolution at this level. One thing which comes to mind relating to this topic is the idea which is still being studied, that cervical cancer may also be caused my male DNA in sperm which interacts with female epithelium causing mutagenesis, especially if the male works in toxic environments.

  7. Josh

    Per the enviromental contaminants suggestion – of note, what was collected were eggs rather than fully mature adults. The eggs *could* have been contaminated, but if they were at such a degree that those contaminants would be widely present in adult cells the shrimp likely wouldn’t have made it to adulthood

  8. Rod Taylor

    Isn’t your headline backwards? The female was a present day female, the males were from the past.

    Sex with someone from the past can be harmful.

    I assume it’s because 1985 shrimp smoked after sex.

    [CZ: I’ll clarify the text. The scientists ran several mating experiments–females got to mate with males from the same year, from the past, and from the future. So, for example, females from 1985 got to mate with males from 1996 and 2007, while females from 2007 got to mate with males from 1985 and 1996.]

  9. This arms race between male and females reminds me the Cold War – both sides are threatening each other and both sides doesn’t really want to unleash all their firepower because they know that doing so would made them extinct.

  10. Ralph Clark

    Can fruit flies or brine shrimp suffer from STI’s ? I thought aquatic species males generally splurge over the eggs after they’re laid but if so then what’s the cuddling all about?

    [CZ: Lots of different ways to make babies in the sea…including amplexus]

  11. So one comes from the future and one from the past. Do they ever both come in the present?

  12. Yes, the females also got to mate with males from their own time. That worked out best for them, as the graph shows.

  13. Jonathan Roth

    “I’m Zaphod Beeblebrox the first, my father was Zaphod Beeblebrox the second, my grandfather was Zaphod Beeblebrox the third and so on…there was an accident with a contraceptive and a time machine.”

    The Restaurant at the End of the Eniverse

  14. David B. Benson

    The answer, of course, is “42”.

  15. Floyd

    42 is the answer, but what is the question?

  16. Jay

    Aside from the dubious methods involved, was there really nothing else with a higher priority? Cancer? Baldness?
    Were I to figure out time travel (or even a Rip vanWinkle trip) and survive, I would be taking victory lap and rockin it like Charlie Sheen on a bender!
    Have towel, will travel.


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The Loom

A blog about life, past and future. Written by DISCOVER contributing editor and columnist Carl Zimmer.

About Carl Zimmer

Carl Zimmer writes about science regularly for The New York Times and magazines such as DISCOVER, which also hosts his blog, The LoomHe is the author of 12 books, the most recent of which is Science Ink: Tattoos of the Science Obsessed.


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