Cichlid prefers to mate with relatives

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A West African cichlid prefers to mate with unfamiliar relatives, rather than unrelated fish, suggesting that inbreeding may help increase its evolutionary fitness.

Pelvicachromis taeniatus, a West African dwarf cichlid, expresses a preference for spawning with related fish that it is unfamiliar with, and shows no signs of developing inbreeding depression.

According to the results of a new study from scientists at the University of Bonn's Institute for Evolutionary Biology and Ecology, which has just been published in the journal Current Biology, inbreeding may be an advantageous evolutionary strategy for Pelvicachromis taeniatus.

"Both sexes of Pelvicachromis taeniatus, an African cichlid with biparental brood care, prefer mating with unfamiliar close kin over nonkin, suggesting inclusive fitness advantages for inbreeding individuals," the authors wrote.

"Biparental care requires synchronous behavior among parents. Since parental care is costly, there is a conflict between parents over care, which can reduce offspring fitness.

"Relatedness is expected to enhance cooperation among individuals. The comparison of the parental behavior of in- and outbreeding pairs showed that related parents were more cooperative and invested more than unrelated parents."

Inbreeding depressionInbreeding depression typically occurs when related individuals reproduce, which can result in deleterious recessive traits, such as deformities, becoming apparent in offspring.

Offspring arising through inbreeding depression often have reduced evolutionary fitness.

The authors wrote: "Inbreeding can be due to random factors (like population size), limited dispersal, or active mate choice for relatives. Because of inbreeding depression, mating with kin is often avoided, although sometimes intermediately related individuals are preferred (optimal outbreeding).

"However, theory predicts that the advantages of mating with close kin can override the effects of inbreeding depression, but in the animal kingdom, empirical evidence for this is scarce."

Moliwe morphThe study used wild-caught Pelvicachromis taeniatus from Limbe, in the Moliwe River in Cameroon, which is only a few miles long and is totally isolated from other river systems.

Both sexes of P. taeniatus significantly preferred to spawn with kin over nonkin, and the mating decisions of females did not differ significantly to those of males.

The authors believe that the fish use phenotype matching to recognise related fish, and that they prefer to stay near related fish.

T Thnken, TCM Bakker, SA Baldaud and H Kullmann (2007) - Active inbreeding in a cichlid fish and its adaptive significance. Current Biology, Vol. 17, 225-229.