Sex with partner is always a good idea

Plants and animals, that have sex with a partner rather than doing it alone via self-fertilization, give their offspring a better chance for longer lives, says a new study.

The researchers reached the above conclusion after conducting more than 100 mini-evolution experiments involving nematode worms (Caenorhabditis elegans) at the University of Oregon.

They found that going it alone increases susceptibility to genetic mutations and reduces that adaptability to changing environments.

Sex with self in the animal and plant world is known as selfing. Offspring born from selfing share all of their genes in common with their parent, and each is capable of producing another generation of offspring.

Offspring from outcrossing share 50-percent of each parent''s genes, and some are born males incapable of bearing offspring.

Selfing populations don''t have to deal with pesky males for reproduction.

In fact, says UO biology professor Patrick C. Phillips, "biologists going all the way back to Charles Darwin have been puzzled why sexual reproduction via outcrossing exists at all."

For the study, the researchers conducted more than 100 trials in which populations of nematodes -- also known as roundworms -- were adapted to new environments, including to the presence of a bacterial pathogen that eats the worms from the inside out.

They genetically engineered the worms, which normally practice a combination of both selfing and outcrossing, to reproduce either just by selfing or just by outcrossing.

They tracked the evolution of 60 different populations for 50 generations under different combinations of mutation, mating system and genetic background.

They found that purely selfing populations were much more susceptible to accumulating harmful mutations and were not able adapt to rapidly changing environments.

Traditional thinking has suggested that selfing populations are able to purge many of these mutations, but this study found that the ability to sufficiently purge was overwhelmed by slight increases in mutation rates, which, in turn threatens the long-term survival of selfing roundworms.

"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," Nature quoted graduate student Levi T. Morran, who was the study''s lead author, as saying.

The study has been published in the journal Nature.