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It's been discovered that female guppies - which practice polyandry (taking multiple mates) - have a mechanism by which they can slow down the sperm of closely-related mates. Amazing!
"It's new and interesting," said Bob Montgomerie, an evolutionary biologist at Queen's University in Ontario, Canada, who was not involved in the research. "If females can prevent fertilization by a close relative, they aren't wasting energy forming a zygote that will likely die due to the accumulation of harmful mutations."
Researchers have long suspected that polyandry evolved in some species as a strategy to reduce breeding with relatives, but lack of evidence for how the females bias paternity after mating has caused the hypothesis to remain simply that.
It's a wierd concept to some dog breeders who have grown up to believe that inbreeding is a good thing but there is a wealth of evidence that the females of many species avoid mating with close relatives. Dog breeders also often try to justify inbreeding by swearing blind that male wolves inevitably mate with their daughters - but this simply isn't true. There's evidence that all wild canids avoid inbreeding. And although they will mate with relatives if there's no option, it appears some at least have the ability to limit the damage. A study of an isolated population of wolves on the Swedish peninsula found that females were somehow able to choose mates that were, genetically, the least related even if, on paper, they were similarly related (Report on Science Daily).
Wild African dogs also practice inbreeding avoidance. A study of a single population in Kruger National Park showed that male and female wild dogs that formed new packs did so only with unrelated members of the opposite sex (Girman et al). This was true even though most males and females dispersed to territories very near their close relatives. Indeed, the researchers found no evidence for inbreeding in the Kruger population.
The domestic dog, however, appears to have, largely, lost this ability - bred out of them by artificial selection imposed on them by us. For every story of a bitch turning her nose up at a brother or father's amorous advances, there is another of one absolutely determined to keep it in the family.
Of course, that doesn't make it right...