Fishy Cooperation, Frans B. M. de Waal
It is commonly thought that animals can be arranged along a ladder of intelligence—
a sort of modern-day Scala Naturae—with humans inevitably at the top, followed by
our close relatives, the primates, all the way down to fish and other slimy creatures.
Over the past decade, this ladder has been challenged by claims of high intelligence
and great social complexity in other animals. For example, spotted hyenas establish
hierarchies in which dominant females support the rank contests of their daughters.
Bottlenose dolphins form “political” coalitions every bit as complex as those of
chimpanzees. Caledonian crow not only use tools in the wild, but also modify tools
in the lab, an ability once thought to define humans.
And now come the fish. It started with a provocative challenge to primate supremacy
with the claim that “culture” or socially transmitted behavior is at least as well developed
in fish as it is in primates. While this may be a bit of an exaggeration, a new study on
cooperative behavior by Redouan Bshary and his colleagues really makes one wonder
if there is anything fish cannot do.
The author describes the astonishing discovery of coordinated hunting between groupers
and giant moray eels in the Red Sea. These two species make a perfectly complementary
pair. The moray eel can enter crevices in the coral reef, whereas the grouper hunts in open
waters around the reef. Prey can escape from the grouper by hiding in a crevice and from
the moray eel by leaving the reef, but prey has nowhere to go if hunted by a combination
of these two predators.
The article describes a grouper and eel swimming side by side as if they are good friends
out on a stroll. It also offers quantification, which is truly hard to achieve in the field, of
the tendencies involved in this mutually beneficial arrangement. The investigators
were able to demonstrate that the two predators seek each other’s company, spending
more time together than expected by chance. They also found that groupers actively
recruit moray eels through a curious head shake made close to the moray eel’s head to
which the eel responds by leaving its crevice and joining the grouper. Groupers showed
such recruitment more often when hungry.
Given that cooperative hunting increases capture success for each of the two predators,
and that they don’t share with each other but swallow the prey whole, their behavior
seems a form of by-product mutualism.
The observed role division comes “naturally” to two predators with different hunting
specializations, and is therefore far simpler to achieve than for members of the same
species. Also, recruitment is quite common in the animal kingdom—for example, primates
have specialized signals to solicit each other’s support in fights. What is truly spectacular
about this study is that the entire interaction pattern—two actors who seemingly know
what they are going to do and how this will benefit them—is not one we usually associate
with fish. This is probably because we tend to develop cognitively demanding accounts
for our own behavior and believe that absent the same cognition, the behavior simply
cannot take place. It is very well possible, however, that our accounts over-estimate
the amount of intelligence that goes into complex behavior. Moreover, we have a
tendency to underestimate the intelligence of animals at lower rungs of the evolutionary
In fact, it is the ladder idea itself that is wrong. The best way to approach animal intelligence
is from an evolutionary and ecological perspective focused on the tasks that each species
faces in nature. In this regard, these two reef predators show us that if it comes to survival,
highly intelligent solutions are within the reach of animals as different from us as fish.
De Waal, Frans B. M. "Fishy Cooperation." PLOS Biology (2006): n. pag. Journals.plos.org. Web. 19 Mar. 2016.
In lines 29-31:
“Given that the cooperative hunting increases capture success for each of the two predators, and that they don’t share with each other but swallow the prey whole, their behavior seems a form of by-product mutualism.”
In this sentence, by-product mutualism is defined as