What do a squirrel and a rattlesnake have in common?

In this post we will talk about coevolution focusing on a practical example between a squirrel and a rattlesnake.

Ever heard of a squirrel that manages to avoid a rattlesnake’s attack, using only its tail? This is a case of coevolution !

Before we answer how this squirrel manages to do something so amazing, let’s talk a little bit about coevolution . You may already know what evolution is (if not, check out this text on Evidence for Evolution ), but what about co- evolution ?

Understanding a little bit of coevolution

Briefly, coevolution is the interdependent evolution between two species, according to important ecological relationships existing between them. 

In the case of the squirrel and the rattlesnake, we have the specific co-evolution between a prey and a predator. Two species that evolved in response to each other [1].

Let’s talk a little about the squirrel and its predator

Our squirrel in question, the California ground squirrel ( Spermophilus beecheyi ). To escape the encounter with its predator , it has developed a simple but effective defense mechanism: the wagging of its tail [2]!

California ground squirrel ( Spermophilus beecheyi ). Source: ResearchGate

On the other hand, the predator , the Rattlesnake ( Crotalus sp), has an organ located between the nostril and the eyes, called the loreal pit , which is responsible for infrared ‘vision’ ( heat radiation ) [3][4].

But what the heck does the squirrel’s tail have to do with the rattlesnake’s infrared ‘vision’?

The squirrel understands that the rattlesnake can detect it by heat, so it increases blood flow to its tail, thereby increasing the heat it emits. This makes him appear larger than the rattlesnake imagined [4].  the squirrel has not increased blood flow to the tail, in the second image the squirrel is wagging its tail and sending more blood to this region, increasing heat emission. Source: NewScientist

It’s as if the squirrel sends the following message: “I’m not a threat, but I’m too big and fast to be worth hunting!”

That way, the rattlesnake gets the message (actually it’s tricked, hehe) and gives up the attack, as it would require a lot of energy and probably wouldn’t be worth all the risk.

The most curious thing is that in the case of confrontation with snakes that do not have the loreal pit , therefore, they do not see the infrared radiation, the squirrel just wags its tail, but does not increase its blood flow [4].

what does all this have to do with the blessed co-evolution?

Everything! The rattlesnake was adapting to hunt using infrared radiation, and the squirrel was also adapting to avoid this attack, this is all part of natural selection (want to know more? Check this blog post!).

It’s the arms race of the animal kingdom! This kind of co-evolution tends to shape more dangerous predators and prey with effective defense strategies [1], winning whoever has the best weapons!

Why should we study coevolution?

With and co- evolution we can understand the interactions of parasites and hosts in agriculture, for example, and thus think of an efficient mechanism for the control of agricultural pests [5].

And also for the preservation and maintenance of biodiversity . By studying coevolution , we understand the various ecological interactions , population control , competition , prey and predator relationships, and food chains.


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