The Super-Trendy Sponge Club
Fed up with the silly rituals of the Skull & Bones at Yale? Had enough of the Ivy Club at Princeton and the pricey clothes and inane conversation at Oxford’s Bullingdon Club dinners? Now you can head over to Western Australia and apply to join the trendiest club in the world. You’ll need high-level social skills and the ability to navigate a lot of in-group politics. And you’ll need a good sponge to wear. Oh, and flippers.
In Shark Bay, off the west coast of Australia, the Sponge Club is the “in thing.” Only a few dolphins know about it, and they only pass their special knowledge on to others who are part of the in-group.
The Sponge Club was founded by a bottlenose dolphin known to scientists and other observers as Sponging Eve. Eve was getting a sore nose while foraging for food in rough sand and broken sea shells. So she tore off a piece of sea sponge and put it on her nose (officially her “rostrum”) and it worked like a charm.
Sponging Eve taught the technique to her kids, and they taught it to a few of their friends. But in the 22 years that researchers were watching the dolphins (and they know from their markings exactly who’s who in the whole region they were studying), they only ever saw 36 dolphins who had taken up sponging. The other 69 either hadn’t learned about it or just hadn’t adopted the technique.
What the researchers also noted was that the spongers were like an elite club. According to the study they’ve just published in Nature Communications:
Spongers were more cliquish, had more sponger associates and stronger bonds with each other than with non-spongers.
… Given that we included only non-spongers that are in the same habitat and had a very high chance of associating with spongers, our results are even more striking. The mutual interests of spongers seem to influence the nature of their social relationships. This is the first demonstration that a behavior that is strictly vertically transmitted by a single parent serves an affiliative grouping function as well, thus meeting both criteria for culture. To date, no material subcultures have been identified outside of humans.
… Like humans who preferentially associate with others who share their subculture, tool-using dolphins prefer others like themselves, strongly suggesting that sponge tool-use is a cultural behavior.
The team, led by Janet Mann of Georgetown University, wrote that these kinds of special associations have played a “critical role in human subcultures.” But before now, there was no firm evidence that these subcultures exist outside of the human world. Now we know for sure that that’s not the case.
Recently, many biologists are moving beyond genetic inheritance to examine the processes involved in inclusive heritability, which includes culture.
We sometimes think that traits such as culture are exclusively human, but a growing body of literature proves otherwise.
If you think this is just about tool use and passing on practical information, that’s not the case. Chimpanzees use sticks to fish termites out of their nests, and elephants use tree branches to swat flies. But in the case of the Shark Bay dolphins, only the calves of sponger females – and only a small number of these – become spongers themselves.
(A) marine basket sponge (Echinodyctium mesenterinum), (B) dolphin wearing a sponge on its rostrum, (C) substrate littered with rock, shell, and debris, (D) hiding prey, barred sandperch (Parapercis nebulosa). All photographs taken by Eric M. Patterson.
As Mann described it to the AFP: “Spongers spend a lot of time hunting, tend to be solitary, but clearly go out of their way when they can to meet up. You could think of them as workaholic dolphins that prefer to meet up with the other workaholics.”
The study also found the behavior was stronger in females, who were better at maintaining alliances. Mann and her colleagues note that while in-group identity has been seen in other animals like orcas, the dolphin sub-cultures are the only ones known, at least so far, to be the result of socially-learned behavior.
The first spongers were discovered among Indo-Pacific bottlenose dolphins in Shark Bay in the mid-1980s, and scientists believe they may have been using this hunting technique for centuries.