Mother Antarctic fur seals (Arctocephalus gazella) alternate between nursing their pups for one or two days and then leaving them to spend days at sea hunting for food. When they return to their breeding grounds, they are confronted with the task of finding their young among thousands of pups. They use vocalizations primarily to locate their pups and scent for close-range recognition. Exactly what part of the pup’s scent, or chemical profile, the mother uses for recognition has in the past been difficult to ascertain, as an animal’s chemical fingerprint comprises a complex array of molecules.
Intrigued by this question, Martin Stoffel and colleagues at Bielefeld University in Germany, along with researchers from the British Antarctic Survey, collected skin samples from mother-offspring pairs in two large colonies of fur seals on Bird Island near South Georgia. DNA analysis of skin tissue determined the genetic composition and relatedness of individuals across the two colonies. Molecular analysis of skin swabs determined differences in the chemical fingerprints of these sampled pairs.
Mother and young were found to have very similar chemical profiles, suggesting a mechanism for mother-pup recognition. Further, the researchers determined that some components of an individual's chemical profile—such as relatedness to other seals—appear to be coded in its DNA, while the presence of other chemicals resulted from environmental influences. For example, a seal’s colony of origin could be determined from its chemical profile, but the same information was not found through DNA analysis.
In seals, as in humans, every gene comes as a pair—one part from the mother and the other from the father. The two parts of the pair can be the same or different. Prior research in fur seals has shown that the more mismatched genes an animal has, the higher its genetic fitness. Stoffel and colleagues revealed that seals with higher numbers of mismatched genes also had more chemicals in their profile. Smelling a male seal’s genetic diversity may help females choose hearty mates.
Stoffel suggests that through the methods used in this study, scientists may be able to sniff out more about vertebrate communication than ever before. (PNAS)