Sniffing out relatives, bluegill sunfish use self-referencing to recognize kin

Researchers have now shown that offspring of promiscuous male bluegill sunfish compare the odor of nest-mates to their own genetically determined odor, and prefer to associate only with individuals that smell like themselves. This finding may explain how social behavior operates in promiscuous animal societies. The new work is reported by Tim Hain and Bryan Neff of the University of Western Ontario and appears in the September 19th issue of Current Biology, published by Cell Press.

Most animals, including humans, are able to recognize their relatives. This is commonly accomplished by remembering the individuals one associates with during early development, such as nest-mates. However, it is now well known that many animals are also highly promiscuous and thus that nest-mates are not always kin (that is, full siblings). A so-called self-referencing kin-recognition mechanism, where individuals use some aspect of their own appearance, odor, or other characteristic to recognize kin, had been proposed for several animals, but past studies had not yet eliminated the possibility that such cases might involve kin recognition based on learning early in development.

In the new work, the researchers studied the ability of bluegill sunfish larvae to recognize kin. Using in vitro fertilization techniques, the researchers created mixed broods in which nest-mates were not reliably kin–some were full siblings and others were unrelated. They then used behavioral experiments and DNA analysis to show that offspring of the promiscuous “cuckolder” males actively sought and associated with the odor of siblings that they had never encountered previously. This ability to recognize unfamiliar relatives provides compelling evidence for the use of kin recognition through a process in which an individual matches its own physical characteristics to those of others, and it confirms the importance of kinship in social behavior.