Nature’s game of rock paper scissors

For as long as life on Earth has existed, there has been a competition for who is the superior member of the species. A competition for who will pass on their genes to the next generation. A certain species of lizard, however, may have locked itself into an eternal game of rock-paper-scissors. The lizard in reference is the Western side-blotched lizard which displays three distinct polymorphic groups. The three groups all display unique mating strategies. Orange variants are naturally stronger and have a more aggressive nature, with males displaying prominent levels of testosterone at around 158 ng/ml on average which allows them to defend a group of females in their territory. Blue males, who display around 40% less testosterone, instead opt for a more monogamous approach, mating with one female per season and guarding her ferociously. Yellow males display around 44% less testosterone than orange males and have a greatly different approach to the other two. By contrast, yellow males do not have any territory, mimicking a female in both behaviour and size, in order to lower the guard of orange males and mate with females that are not in the vicinity of one. This is where the idea of rock paper scissors comes in: orange males have greater physical prowess in comparison to blue males, meaning they can overpower them in order to steal the blue male’s guarded female; Yellow males counter orange males as they use stealth in order to mate with unguarded females within the orange male’s territory and blue males oppose yellow males as they are constantly guarding their mate, meaning yellow males are unable to get close to the female. This is an example of evolutionary game theory, as there is a set number of ‘moves’ each individual can make. Using the replicator equation, which shows the fitness of groups in a population, it shows that there is no genetic advantage across the three subgroups. This means that the population will become an example of an evolutionary stable strategy (ESS) which means that regardless of the situation, each subgroups approach towards mating will always stay the same, as it yields the greatest benefit, locking them in said cycle of rock paper scissors. The process of evolution should mean that there must be a definitive dominant group within the species, resulting in the other less fit groups being unable to compete with the dominant group, therefore dying out. Preventing this, however, is that the females of the species tend to go for an abnormal mating strategy. Although females similarly follow the colour patterns and behaviours the males display and tend to prefer males of the same colour, when a polymorphic groups population dips below the other variants, females begin to prefer the rarer colour of the season. This means that if there is a lack of one group, e.g. blue males, the females bring the population of the blue lizards up to the rest of them. Now, the obvious solution to stop this endless cycle of rock paper scissors is just to remove one group from the breeding population, right? Well, female western side-blotched lizards have already counteracted that plan. By changing the levels of hormones like testosterone, females can change the colour and therefore inherent behaviour of their offspring. This has been done previously, using adult male yellow lizards, and increasing their levels of testosterone. The results showed that male yellow lizards gained a blue throat colour, as well as an increased level of endurance and aggressiveness of around 49%. This proves that the species’ subgroups are directly determined by hormones, more specifically testosterone, proving the ability for the lower populated groups population to be brought back up. For over 15 million years this game of rock-paper-scissors has been going on. For over 15 million years this unique species of lizard has taken its own path of evolution and undoubtedly will continue for the foreseeable future. It is indisputable that evolution has allowed us to marvel at this cycle and when all other species are forced to evolve and change, these little lizards will still be playing their game.