The perpetual card game

Yesterday morning my supervisor, a fellow PhD student and myself looked like a lab that had resorted to acquire funding through gambling. In fact I think a lot of passers-by really thought this was the case.

This wasn't just any card game though. This was a perpetual game of coevolution where no-one would ever win and you effectively worked to stay in the same place.

So why the hell were we doing this?

The process of coevolution is where species that interact in nature adapt to the presence of each other. Since each species changes as they adapt to the other they are constantly moving targets. As a result there exist cycles of continual reciprocal adaptation.

As you can see this is a difficult concept to explain without looking at how it actually happens. Conveniently there are really cool examples of coevolution in nature. One of which is the coevolution of parasites and their hosts. Here a parasite evolves to infect the host, then the host evolves to resist the parasite. Because of this the parasite has to evolve to adapt to this new host and so on and so forth.

With the aim to teach the concept of coevolution Amanda Gibson, Devin Drown and Curtis Lively developed a card game to demonstrate how hosts and their parasites coevolve (http://www.evolution-outreach.com/content/8/1/10).

This card game basically uses the card suits (club, diamond, spades and hearts) as different parasite strategies to infect the host and the same suits are used by the host as strategies to resist the parasite. So when a diamond parasite meets a host of any suit other than a diamond it successfully infects and kills the host. But when it meets a host matching its suit (here a diamond host) that host is resistant and the parasite dies. The game works by rounds, or' generations', where each individual (a host or parasite card) that hasn't died in that round has offspring of the same suit (representing asexual reproduction) which form the next rounds individuals (see step by step diagram below) What is pretty cool is that by scoring the frequencies of each suit for the parasites and hosts at each round you get a graph that shows how parasite and host strategies fluctuate and track each other over time in a process of coevolution.

In the graph below you see that when a club host (dark blue) becomes common, club parasites (light blue) spread and become common as they can infect that host. Then when other host strategies become common because the club hosts are dying other parasite strategies will follow suit (really proud of this pun), resulting in fluctuations of parasite and host types.

What's REALLY cool is that these cycles are what we see in nature between hosts and parasites.

These cycles are often referred to as 'Red Queen dynamics'. In Chapter 2 of 'Through the Looking Glass' (Carroll 1872) the Red Queen says to Alice "Now, here, you see, it takes all the running you can do to keep in the same place".

It appears that hosts and parasites also have to "run" (evolve) in order to stay in the same place (exist).

Because science.