ScienceDaily (Oct. 4, 2006) — Many animal societies involve highly promiscuous mating behavior, making it potentially complicated for individuals to recognize and preferentially help their relatives. 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.

The researchers include Timothy J.A. Hain and Bryan D. Neff of University of Western Ontario in London, Ontario, Canada. Research conformed to protocols outlined by the Canadian Council on Animal Care and was supported by the National Sciences and Engineering Research Council of Canada (scholarship to T.J.A.H. and grant to B.D.N.).

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Adapted from materials provided by Cell Press, via EurekAlert!, a service of AAAS.

A mating trio of bluegill sunfish consisting of a parental male (left), a female (center), and a cuckolder male that mimics a female in coloration and behavior. Despite the clever deception of the cuckolder male, a parental male still manages to sire a majority of the eggs within his nests. Consequently, his offspring are highly related to most of the young within the nest, and his offspring do not differentiate among kin and nonkin when associating with nestmates. Conversely, the offspring of cuckolder males are typically unrelated to many of the young within a nest, and unlike the parental male's offspring, cuckolder offspring compare the similarity of a putative kin's odor to their own odor to find nestmates that are kin (this method is referred to as self-referent phenotype matching). For more details, see the article by Hain et al. in Current Biology. (Credit: Current Biology)

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