New paper throws doubt on a popular idea

Posted by on Oct 9, 2020 | 0 comments

The rock-paper-scissors story of the side-blotched lizards was beautiful. Many lizards have similar colour polymorphism, and quite a few PhD projects and postdoc years have been spent testing the idea in other species. One of the most obvious candidates are wall lizards, where several species come with clearly distinct white, yellow and orange/red throats and bellies. The early reports were – as they often are – encouraging. But researchers throughout Europe grew increasingly worried that the phenotypic differences between red, yellow and white animals at best were small and inconsistent or, at worst, entirely absent.

Alternative mating strategies tend to be manifested behaviourally. We therefore decided to release common wall lizards of the three main colour morphs in large outdoor enclosures in Moulis and observe what they actually do. The prediction is simple: if the morphs signal relevant aspects of sociosexual behaviour, such differences should be evident in how the lizards interact with one another, or who they chose to mate with.

We had done similar studies before, both in Moulis and in Oxford, and it works like a dream. As long as there are people truly dedicated to watching lizards, that is. Thankfully, the lead author of the study – Javier Abalos – is very patient and, quite frankly, obsessed with lizard watching.

With a huge amount of behavioural data collected, home ranges quantified, and paternity secured, Javier could conclusively say that there is nothing going on. Nothing, Nada, Inte ett dugg.

There is of course always the possibility that lizards do something else when they go about their business outside of field enclosures. So Javier and another obsessive lizard watcher – Guillem Perez I de Lanuza – added a long term field data set to the mix. Again, no evidence that males or females of different colour morphs behave differently, or that they modify their behaviour depending on the morph of other individuals.

Conclusion: Whatever these colours mean, they certainly do not signal differences in social or sexual behaviour. At least not in this lineage of wall lizards. You can read the full story here.

The problem, of course, is that it is very difficult to prove that there is nothing going on. It is also very unpopular when data fail to support a good old adaptive story. So reviewers try hard to come up with reasons for rejection – it can almost be endearing to read attempts to rescue a favourite hypothesis. But efforts like those from Allen Moore and the editors of Ecology & Evolution ensure a swift publication of unpopular findings. Chapeau to the editor for their frank evaluation of the reviewer comments from a different journal. Such encouragement is especially important for early career researchers so they won’t be put off by people who care more about their ego than about what the results say.

Nevertheless, at the end of the day, there must be some kind of explanation for why these morphs persist. They are even found in several other wall lizard species. But after Javier’s results you would have to be an optimist beyond belief to think they signal alternative behavioural strategies. If you have different ideas and want to test them, please don’t hesitate to get in touch.

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