Rock-Paper-Scissors-Lizard-Lizard-...Lizard?

If you've ever seen the TV series 'The big bang theory' then you should know about rock-paper-scissors-lizard-spock, the classic alternative to the game rock-paper-scissors. However, I bet you've never heard about the all lizard variant lizard-lizard-lizard.

Rock-Paper-Scissors-Lizard Spock. Image credit: DMacks (Wikimedia Commons)

Unlike the other versions, lizard-lizard-lizard is actually played in real life between lizards, and involves the competition between different colour morphs of the side-blotched lizard, all differentiated by having different coloured throats. So, without any further ado, I guess it's time to meet our contenders.

In the orange corner!

The big orange fighting machine. This hulk of a lizard is the 'ultra-dominant' male. These guys keep and defend a pretty large territory for lizards their size (≈100 m²). Their size and power come with some great advantages. Holding this much territory means that they have access to a lot of female lizards, and they can also steal mates from some of the weaker smaller lizards.

But there's also some disadvantages to having territories that large. See, with a territory that large it can be impossible to keep track of everyone inside your territory, but we'll come back to this later.

The 'ultra-dominant', orange-throated side-blotched lizard. Image credit: Joshua Tree National Park (Flickr)

In the blue corner!

The lizard in blue. This guy is a 'dominant' type, he's not as strong as his orange cousin, but he's strong enough. His territory is a lot smaller but for him it's the perfect size, just enough space for him and his girlfriend.

Because he doesn't have much territory it's easy enough for him to protect his girlfriend from any weaker, smaller lizards, but if a bigger male lizard steps into his territory and attempts to make off with his girlfriend then there's not really much he can do to stop them.

The 'dominant', blue-throated side-blotched lizard. Image credit: Max Pixel

And in the yellow corner!!!

The yellow-throated males are the 'sneakers'. They tie this whole game together. They may not be the strongest fellows, but they're much sneakier than the other two. So if it came to a direct confrontation they'd lose every time, however, they can easily make their way around by avoiding confrontation. 

The greatest tool in the yellow males arsenal is his amazing ability to cross dress. These lizards have almost the exact same colour scheme as some of the female lizards. This means they can easily sneak into big territories and act as if they're just another one of the females from around the block, but if a male comes to mate with them they can also pull of a pretty good imitation of the female rejection display, and luckily these lizards understand that no means no.

The 'sneaker', yellow-throated side-blotched lizard. Image credit: Jacksnipe1990 (Flickr)

Fight!

Some of you may have figured out already how all these colour morphs tie together, but for those who haven't here's the rundown.

Orange lizards are big and strong and so they can steal mates from the weaker blue lizards. However, these blue lizards are adept at noticing strangers in their territory and so they can protect their mates from the yellow lizards. Finally, yellow lizards can use their cross-dressing attire to slip into the orange lizard's territory for a sneaky quickie with the female lizards there. This is known as a biological game of 'rock-paper-scissors', aptly named due to the fact that each colour morph has advantage over one colour morph but is at a disadvantage against the other.

Orange beats blue, blue beats yellow, and yellow beats orange. Authors own (created with Canva)

Now these throat colours aren't just fashion statements. They're genetically determined. It's a relatively simple example of Mendelian inheritance, with only three alleles (variations of a gene) involved. the three alleles are o, y, and b (sensibly related to orange, yellow, and blue morphs respectively). o is dominant to all other versions, y is dominant to b, and b is recessive to all of them. This means that lizards with the genotype (the combination of alleles inherited from their parents) oo, oy, and ob will become orange morphs, lizards with the genotype yy and yb will become yellow morphs, and blue morphs will always be bb.

In essence, this means that the more successful one colour morph group is, the more of that colour morph will be born (i.e. the better orange males are doing, the more there will be orange children born). this, combined with the rock-paper-scissors effect, means that the population goes through an interesting 4-5 year cycle.

So, let's say we start with a population where the orange males are currently very successful. This means they have a lot of territory and are probably stealing a lot of mates from the blue males, but also means there's more territory for the yellow males to infiltrate. So the yellow males start to become more successful and start stealing more mates from the orange males, but they're vulnerable to the blue males who are more than capable of defending the one mate they have. So the blue males start to become more successful and cause a decline in the yellow males, but the orange males can now steal more mates from the blue males. So, finally the orange males become more successful again and the cycle starts over.

This is known as frequency-dependent sexual selection, because the reproductive success of certain morphs depends on the relative frequency of the different morphs in the population. This weird cycle proves that no one type is better than another in a good old-fashioned game of lizard-lizard-lizard.

You can read more about these amazing lizards here and here.