Time-travel sex: Bad for sea monkeys

Study shows female brine shrimp survive longer when they don't mate with "males from the future or the past"

Published June 17, 2011 7:18PM (EDT)

For a new study set to be published in the journal Evolution, scientists from the Center for Functional and Evolutionary Ecology in Montpellier, France, mated female brine shrimp ("sea monkeys") with males from past and future generations.

The report, called "Male-Female Coevolution in the Wild: Evidence from a Time Series in Artemia Franciscana," found that the female brine shrimp "survived better and had longer interbrood intervals when mated with their contemporary males compared to when mated with males from the future or the past." Its formal conclusion: "[T]he process of male-female coevolution, previously revealed by experimental evolution in laboratory artificial conditions, can occur in nature on a short evolutionary time scale."

How is it possible for females of a species to breed with males from past or future generations? For brine shrimp, it's actually easier than you might think. Science writer Carl Zimmer explains:

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. [Study leader Nicolas] 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.

What happened next? Zimmer summarizes:

Rode and his colleagues ... discovered ... 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%.

The report's suggestion that female shrimp are better suited to mate with their contemporaries than with males from the past or future seems to corroborate the theory that "sexual conflict is an ongoing process," with males and females adapting new mating "strategies" in concert or in competition with each other over time, Zimmer writes -- although it's still not clear what sort of pattern the conflict might follow (nor is it obvious, in this particular case, exactly "how the time-traveling males [harmed] the females").

Just to be safe, though: If your dream historical dinner party with Cleopatra, Henry VIII and Napoleon ever does happen, you might want to consider heading home early.

By Emma Mustich

Emma Mustich is a Salon contributor. Follow her on Twitter: @emustich.

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