Scientists: Sex with a partner better than 'selfing'


Levi Morran, a graduate student at the University of Oregon, had the pleasure of watching 50 generations of roundworms procreate and concluded that, as problematic as males are, sex with a mate is better than sex alone. University of Oregon

Sex with oneself in the world of plants and animals is called, fittingly, "selfing." The offspring of selfing females share 100 percent of their mothers' genes, and they can go on to produce their own offspring.

The offspring of "outcrossing" (the sexy science term for mating) males and females, on the other hand, share 50 percent of each parent's genes. Some offspring, naturally, are males that cannot bear offspring.

Of the two systems, it turns out that outcrossing produces offspring whose more diverse genetic codes lead to greater chances for longer lives, lower susceptibility to genetic mutations, and better adaptability to changing environments, according to more than 100 mini-evolution experiments with nematode worms at the University of Oregon. Researchers are reporting their findings, among creatures that can reproduce via both selfing and outcrossing, online on Wednesday in advance of regular publication in the journal Nature.

While selfing females don't have to put up with "pesky males" to reproduce, a problem known as the evolutionary "cost" of males, and they can, in fact, populate twice as quickly when going it alone, the genetic benefits of outcrossing explain why the phenomenon exists at all, the researchers explained.

"Biologists going all the way back to Charles Darwin have been puzzled why sexual reproduction via outcrossing exists at all," said UO biology professor Patrick C. Phillips, who turned to two of his students in the UO Center for Ecology and Evolutionary Biology to help determine what good could possibly come of worms having partners.

Levi Morran and Michelle Parmenter conducted more than 100 mini evolutions for 50 generations, in which 60 populations of nematodes, also known as roundworms, were adapted to new environments, including to the presence of a bacterial pathogen that eats worms from the inside out, according to a statement.

Morran and Parmenter genetically engineered the worms, which normally practice a combination of both selfing and outcrossing, to reproduce just one or the other. Strictly selfing populations, they found, were far more susceptible to accumulating harmful mutations and unable to adapt to rapidly changing environments.

"The inability of selfing populations to adapt to changing environmental conditions helps to explain the observation that selfing populations are much more likely to go extinct than outcrossing populations," says Morran, a graduate student and lead author of the study.

While males are clearly problematic for several reasons, their evolutionarily benefits do outweigh their costs, Phillips concludes. Sound familiar, ladies?

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