A baby lamb is separated from its family. Somehow, in vast herds of sheep that look virtually identical, the lost youngling locates its kin. Salmon swim out to the vast expanses of the sea and migrate back home to their precise spawning grounds with bewildering accuracy.
Scientists have long known about such animal kinship attachments, some known as “imprinting,” but the mechanisms underlying them have been hidden in a black box at the cellular and molecular levels. Now biologists at the University of California San Diego have unlocked key elements of these mysteries, with implications for understanding social attraction and aversion in a range of animals and humans.
Davide Dulcis of UC San Diego’s Psychiatry Department at the School of Medicine, Giordano Lippi, Darwin Berg and Nick Spitzer of the Division of Biological Sciences and their colleagues published their results in the online issue of the journal Neuron.
In a series of neurobiological studies stretching back eight years, the researchers examined larval frogs (tadpoles), which are known to swim with family members in clusters. Focusing the studies on familial olfactory cues, or kinship odors, the researchers identified the mechanisms by which two- to four-day old tadpoles chose to swim with family members over non-family members. Their tests also revealed that tadpoles that were exposed to early formative odors of those outside of their family cluster were also inclined to swim with the group that generated the smell, expanding their social preference beyond their own true kin.
The researchers discovered that this change is rooted in a process known as “neurotransmitter switching,” an area of brain research pioneered by Spitzer and further investigated by Dulcis in the context of psychostimulants and the diseased brain. The dopamine neurotransmitter was found in high levels during normal family kinship bonding, but switched to the GABA neurotransmitter in the case of artificial odor kinship, or “non-kin” attraction.