Mate choice is often the most important decision in the lives of humans and animals. This also holds true for Arctic animals. Scientists at the Konrad Lorenz Institute of Ethology at the Vetmeduni Vienna have compared the preen gland chemicals of black-legged kittiwakes with genes that play a role in immunity. Kittiwakes that smell similarly to each other also have similar genes for immunity. Since the birds prefer to mate with unrelated mates, the scientists have now found the likely mechanism by which they recognize relatedness.

Kittiwakes are among the most numerous Arctic birds. They build their nests as colonies in cliffs around the Arctic.
Kittiwakes are among the most numerous Arctic birds. They build their nests as colonies in cliffs around the Arctic.

It has long been understood that reproducing with close relatives may have profoundly negative effects on offspring. It is therefore not surprising that biologists have discovered in some species that breeding individuals have evolved ways to detect their genetic similarity with those of prospective partners. Especially the immune system plays an important role in the mating preferences. The more dissimilar the immune system of the parents, the healthier the offspring. In mice as an example of mammalian disease resistance, the female recognizes the relatedness of a potential male on its urine. The bigger the difference of the relatedness, the better for the offspring. But what about non-mammalian animals like birds?

The secret lies in the preen gland

This mystery appears to have been solved by a group of researchers from Austria and France. Team leader Richard H. Wagner and behavioral geneticist Wouter van Dongen of the Konrad Lorenz Institute of Ethology, a part of the Veterinary Medicine University Vienna, have been collaborating with French colleagues on a long-term study of a cliff-nesting gull, the black-legged kittiwake, breeding in Anchorage Bay, Alaska. When birds groom themselves with their bills, they spread chemical compounds from their preen glands throughout their plumage. These chemicals produce odors that appear to be unique to each individual, providing an olfactory fingerprint. The team suspected that, just as in mammals, these odors may be used by kittiwakes to assess their relatedness to other individuals.

Male kittiwakes often try to mate with females who already have found their appropriate mate. This causes a lot of tension between different males.
Male kittiwakes often try to mate with females who already have found their appropriate mate. This causes a lot of tension between different males.

Show me, how you smell. I tell you if you fit

The team had previously discovered that kittiwakes avoided pairing with relatives, but the mechanism by which the birds recognized their relatedness to each other had remained unknown until now. Their new finding is that individual kittiwakes that smell similarly to each other (i.e. have similar preen gland chemicals) also have similar specific immune genes. Closer relatives therefore have more similar odors than distantly related individuals. This suggests that birds may be able to compare their own odor with those of potential mates, and to choose unrelated individuals as breeding partners. Quips ornithologist Wagner, “the more research that is performed on smell, the more it appears that anything mammals can do, birds can do too.” The new findings, moreover, open the door for further work linking mate choice and disease-resistance in birds.

If the chick hatches and can be raised by its parents, it stands a good chance of survival due to its healthy and strong immune system.
If the chick hatches and can be raised by its parents, it stands a good chance of survival due to its healthy and strong immune system.

Quelle: Veterinärmedizinische Universität Wien,  www.vetmeduni.ac.at