In June 2018, we sampled 13 wild populations of common lizard in the Cevennes National Park (South-Central France) to explore the relationships between colour signals, morphology, performance, parasitism, testosterone, and ecogeographical variables. We found that UV signals were good indicators of male quality (i.e. sprint speed) and their expression increased to compensate degraded light conditions, as expected from theoretical background.
In August 2018, we manipulated the testosterone levels of subadult common lizards during two weeks to see whether or not it affected their coloration, including UV, their performance and morphology. We then measure these same lizards once a month during 10 months as they reached sexual maturity to detect any long-term effects of our testosterone treatments. These results will allow us to detect whether signal honesty can be mediated by testosterone early in the ontogeny and affect signalling level at sexual maturity.
Then, we performed a similar experiment but this time in adult lizards to understand the potential role of testosterone in UV signalling in the short term. We did this experiment on males from two lizard species, the common lizard (Zootoca vivipara) and the common wall lizard (Podarcis muralis). This experiment took place in spring 2019. We manipulated testosterone levels during two weeks and measured the lizards’ performance, morphology, coloration, metabolism, and immunocompetence before and after treatments. These results, along with the ones from the previous paragraph, will tell us whether testosterone mediate physiological costs associated with the expression of UV signals in these lizards.
In spring 2019, we performed a behavioural experiment aiming at identifying the potential social costs associated with UV signals during male agonistic contests. We found that social costs indeed participate to enforce UV signal honesty in common lizard. This study has been published as an open access preprint on the public repository Zenodo and is currently under review for publication in a peer-reviewed scientific journal.
In spring 2019, we started an experiment to investigate whether or not predation costs were associated with UV signals. To do so, hundreds of common lizards (males, females, and subadults) were placed in 25 outdoor enclosures reproducing semi-natural conditions. Half of these enclosures were covered with antipredation nets while the other half was vulnerable to bird predation. We measured the coloration and morphology of all lizards and recaptured them in spring 2020 to test whether or not predation occurred and whether it targeted individuals based on their coloration.
We assembled a large data set from many years of study on common lizard coloration that took place at the CEREEP-Ecotron, the experimental station where most of this project took place. This data set will allow us to test whether UV signals are heritable by analysing whether sons have UV signals more similar to their father and brothers than to other male lizards, controlling by lizards age. Knowing this will pave the way to future research aiming to identify the genetic markers responsible for UV coloration in this species.
Finally, in spring 2019, we released in ten large outdoor enclosures reproducing semi-natural conditions adult males and females and let them compete and reproduce as naturally as possible. We took their coloration, performance and morphological measurements and recaptured the gravid females to performed paternity tests. The Covid-19 crisis interrupted the paternity analyses but they will be resumed as soon as possible. This study will improve our understanding of the role of UV signals during the reproductive season, especially with a measure of reproductive success.
