Say the word inbreeding and the image that comes to mind is of a cross-eyed, slobbering monarch sitting on his throne next to a queen who is also his sister.
But while inbreeding in humans can have disastrous consequences, scientists now find it can have its upside in the wild. Animals in the wild often avoid close kin as mates because inbreeding causes harmful genes that might otherwise recede into the background to show up in progeny more often.
However, recent theoretical predictions suggest sometimes the benefits of inbreeding might outweigh the costs. Evolutionary biologist Timo Thünken at the University of Bonn in Germany and his colleagues have uncovered evidence to support these predictions. Thünken and his colleagues reported their findings in the February issue of the journal Current Biology.
The scientists investigated the African cichlid Pelvicachromis taeniatus, a small monogamous fish that lives in the rivers and creeks of Cameroon and Nigeria. Males occupy caves, while females compete with each other for males.
"We initially wanted to investigate whether P. taeniatus avoid kin as mating partners, because it has been shown in other species that inbred offspring have disadvantages -- for example, increased mortality," Thünken explained.
"First, we conducted a female choice experiment," he said. This involved aquariums with breeding caves for males and hiding places for rejected females.
"Against our expectations, females did not avoid brothers, but even preferred them," Thünken told LiveScience. This proved true in 17 of 23 experiments.
Both parents in the species care for their young to protect them against predators, the researchers noted. This requires high levels of cooperation.
Since kinship generally favours cooperation, Thünken and his colleagues theorised related parents did a better job of cooperating than non-kin. Their observations supported their ideas, finding that inbreeding pairs spent significantly more time accompanying their free-swimming young.
They also discovered males of inbreeding pairs spent significantly more time guarding breeding caves and were half as likely to attack their mates.
The researchers also discovered inbreeding did not appear to lead to higher rates of harmful gene expression. However, Thünken and his colleagues noted inbreeding might affect traits they have not yet studied, such as the fertility of offspring.
The scientists plan to look next at the level of inbreeding in natural populations of the fish, the fitness consequences of inbreeding and the mechanisms of kin recognition in the species.