During the course of a single day, think of all the different people with whom you come into contact.
This may include close or well-known associates such as family, friends, and co-workers, in addition to lesser-known acquaintances such as passers-by on the sidewalk, passengers on the commuter rail, attendants and shoppers at the grocery store, and fellow members at the gym.
With each new person that we encounter, we form a different type of group. In fact, we form so many different types of groups every day that we don't even consciously think about it.
This type of social dynamic — where we are constantly joining and splitting from groups and interacting with different people ¬— is called "fission-fusion" (meaning "split" and "join") and is also common amongst non-human mammals such as whales and dolphins.
While fission-fusion dynamics are characterized by a high degree of fluidity, there is also stability in that some bonds persist regardless of the situation. Think of the person with whom you spend the most time and form your strongest bond (for example, your spouse, parent, child, or best friend). Then, think of all the different types of groups you form with that person. While the context may change, the one constant is that you are with that other person — it is a stable bond in the midst of your constantly changing social environment. You may also form bonds with people that are limited to certain activities, such as walking buddies, carpool companions, or other parents at your child's swimming lesson. When you start to think about these details of your social network, it quickly becomes quite complex!
Now, imagine forming these close bonds and keeping track of these ever-changing social relationships under the sea, without the use of language or even enough light to see everyone in the group. This is how many whales and dolphins navigate through their social world. However, they use a suite of other adaptations to keep in touch with each other, such as intricate vocalizations which may travel great distances underwater, highly enervated skin for tactile sensory communication, and above-water leaping displays.
Fission-fusion dynamics are especially prevalent among members of Family Delphinidae, or dolphins. Similar to people, many dolphin species live in highly fluid societies where group size and membership frequently change. However, within these fluid dolphin societies, some individuals form long-term bonds and associate preferentially during certain behaviors. For example, male bottlenose dolphins form partnerships that may persist for 20 years, and dusky dolphins have preferred companions when working together to feed on small, schooling fish.
Since 1979, the Whale Center of New England has studied the social lives of whales and dolphins inhabiting the southern Gulf of Maine.
Among the dolphins we have studied, it is likely that Atlantic white-sided dolphins exhibit fission-fusion dynamics; however, we still have much more to unravel about this species' social system. In contrast, the social behavior of humpback whales has been intensively studied by the Whale Center for 30 years. Our long-term research has revealed that humpback whales also exhibit fission-fusion dynamics, characterized by small groups with fluid changes in membership and preferential companionship. Such patterns are particularly evident when humpback whales coordinate feeding behaviors, for example by blowing bubbles to corral fish.
Fission-fusion dynamics are not limited to humans and cetaceans, however. Other mammals such as elephants, hyenas, and several primate species also display this juxtaposition of stable bond formation in the midst of an ever-changing social world.
This ability to keep track of relationships in a chaotic social environment is closely linked to brain size and intelligence — a topic which I will be exploring in my next column.
Dr. Heidi Pearson is assistant director and stranding coordinator for the Whale Center of New England, based at Harbor Loop in Gloucester.