For Some Species, An Upside To Inbreeding:
Although breeding between close kin is thought to be generally unfavorable from an evolutionary standpoint, in part because harmful mutations are more easily propagated through populations in this way, theory predicts that under some circumstances, the benefits of inbreeding may outweigh the costs.
Researchers have now reported real-life evidence in support of this theory. Studying an African chiclid fish species, Pelvicachromis taetiatus, in which both parents participate in brood care, the researchers found that individuals preferred mating with unfamiliar close kin rather than non-kin.
Actually, this same result was obtained in Japanese quail about 20 years ago or so. The quail breeding colony I worked with is extremely inbred and is thriving. Contrary to expectations of some others in the lab who were trained in classical population genetics, I was confident that we are not going to see a sudden crash of our population due to inbreeding and I was right for all these years.
Because parental work is energetically costly, and kinship generally favors cooperation, one possible explanation for kin preference in breeding in this species is that it offers a benefit by facilitating parental cooperation. And indeed, observations of behavior exhibited by this chiclid species showed that related parents were more cooperative and invested more resources in parenting than did non-related parents.
Together, the findings suggest that, somewhat unusually, active inbreeding is advantageous in this fish species. The findings, reported by Timo Thünken and colleagues of the University of Bonn, appear in the February 6th issue of Current Biology.
Actually, as quail live in tightly-knit coveys of about 10-12 individuals (and the Asian species, livig up in Siberia, may never split the coveys in spring due to thermoregulatory advantages of covey-living), this was exactly the explanation I had for the advatntages of inbreeding in our quail colony.
You can read the actual paper here:
Active Inbreeding in a Cichlid Fish and Its Adaptive Significance
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Surely this is not something that will work for most species -- there has to be a pretty good payoff to outweigh the cost of amplifying recessive mutations. Either that, or it works in species in which there is no great cost, because no great load of deleterious mutations -- e.g. long selection in a harsh environment produces a relatively "clean" genome?
Absolutely! I should have said that in the post myself, but got in the "that is obvious" frame of mind. It may not be as obvious to someone who does not think about this all the time.
Indeed, it really depends on the genetic load.
In some organisms that are used to recurrent selfing, i.e. most hermaphroditic plant species (and it's quite a lot of species diversity, wouldn't be?), there is a evolutionary tradeoff between inbreeding depression levels (potential disadvantage of selfing due to genetic load) and diverse advantages of selfing (among which reproductive insurance in small populations, local adaptation/escape of outbreeding depression, automatic-transmission advantage of selfing etc).