Chemical kin recognition in the beaver (Castor canadensis): Behavior, relatedness and information coding

I studied kin recognition in the North American beaver (Castor canadensis) in Allegany State Park, New York, from 1992 to 1995. Field tests showed beavers can discriminate between unfamiliar relatives and unfamiliar non-relatives by the anal gland secretion (AGS) only, but they failed to show this discrimination when castoreum alone was presented. Thus, the information about kinship is contained in AGS but not in castoreum. The cue used for kin discrimination can be learned from a third but related individual. These results demonstrate that the phenotype matching mechanism is used in beaver kin recognition. Using gas chromatography, I found the within-individual variation in the AGS is small over time and space. Between-individual comparisons showed that related individuals are more similar in their AGS profiles than non-related individuals. Hence, the similarity in the AGS profile provides a reliable clue for beavers to recognize their relatives. Consequently, the AGS can be called a "kinship pheromone". Further investigation demonstrated that not all compounds in the AGS profile are equally important. Families can be classified accurately using only three compounds in males or two compounds in females. With progressive addition of compounds, the classification accuracy decreases first and then increases to 100%. This suggests that either beavers use few compounds or many compounds for kin recognition. Additionally, information about family membership is a special case and thus, a by-product, of that about relatedness. The heritability of almost all of the individual AGS compounds is close to zero. However, the heritability of the AGS profile represented by the first three principal components seems moderate to high. Consequently, I infer that the genes controlling the production of AGS are tightly linked. This eliminates the possibility of using few compounds to code for the information about relatedness. The use of many compounds makes it possible to incorporate more digital components in information coding than the use of few compounds. Therefore, beavers show adaptation in reducing the ambiguity in communicating information about kinship.