Have you ever wondered why humans are able to use tools? Is it because of our big brain? Our capacity to move objects precisely with our hands? In other words, what are the factors that allows tool use to evolve? It is a difficult question to answer because we can't teleport into the past to see what features humans have when they start using tools. What we can do is study other species that use tools, look at what features they have (sociality, brain size, etc) and see if a general trend appears: A feature that is always present in species using tools. This type of analysis is called comparative phylogenetic analysis*.
The problem is that tool use is a very rare behaviour in the animal kingdom. It is impossible to draw general trends from a few occurrences! That is why we need to explore tool use in all vertebrate species.
By studying tool use in fish, we might be able to unravel the factors driving tool use evolution and explain why tool use is a rare behaviour in the animal kingdom given the potential high advantages it provides.
In our research project, we focused on one type of tool use: anvil use. When using an anvil, the fish grabs a prey item (typically an urchin or clam) in its mouth, swims to a specific rock/coral and uses it as an anvil by rapidly and repeatedly bashing the prey item until it breaks. It is a case of tool use as the fish is using an external object to achieve an immediate goal. The behaviour extends its physical capabilities: It would not be able to crack this clam with its teeth! And also its limits the possible damage in the mouth from broken shells or urchins.
Anvil use has been described in 15 fish species so far. All these species belong to the Labridae family or wrasses. A huge family with more than 600 species (twice the number of primate species) and very diverse in terms of ecology, diet and life-history. This means great opportunity for comparative analysis! Because we have 1- a lot of occurrences of anvil use evolution, and 2- species exhibiting diverse features (you can't do comparative analysis when all family members have the same features).
What species use anvils to crack open prey? Are species using different techniques? Are all individuals within a species using the same technique? We must document anvil use in all species before doing comparative analysis. How will we do that?
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Most species described using anvils so far are coral reef species and occurs at the Great Barrier Reef. We plan to film them when they are using anvils. To help us find the rocks/corals used as anvils, we will spot middens of broken shells. Fish seems indeed to have a “tool preference” – that is a preferred rock/coral where they go back to crack open prey and step by step building a midden of broken shell!
Once we determined all fish species using anvils and their techniques, we would be able to map this information on the phylogenetic tree of fish and determined how many times anvil use appeared in the evolutionary history of fish.
Here is the time for the comparative analysis! We will extract from the literature all important features of the Labridae species and then statistically test for any correlation between tool use and multiple other features. We expect to find that brain size (whole brain or specific brain areas) is an important factor driving the emergence of anvil use, confirming that tool use evolves as part of an intelligence syndrome. As tool use rarely evolves, we expect to find other factors than cognition involved in anvil use evolution. Physical factors should be involved as using tools is more difficult underwater than in land given the water viscosity. We thus expect to find anvil use in fish of large size and with great strength in their mouth. And we might have surprises!
Most studies of tool use focus on primates and birds. How primates/birds use tools is necessarily different from fish. The rules of physics differ considerably between land and underwater. Water is more viscous making any rapid moves more difficult and everything more buoyant. fish cannot drop a rock from a certain height on a prey and wait for gravity to do the rest. fish also lack grasping appendages such as hands or feet. We need to study tool use in to get a more complete picture of tool use in animals.
Fish are clever animals Their true cognitive abilities are far from the common belief of dumb animals. As tool use is considered as a hallmark of intelligence, we hope to help deconstruct this image. Check this e-learning to learn more about how smart are fish.